Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: mcandmar on December 03, 2013, 02:10:53 PM
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I figured i would document the modifications i have done to lower the background hum of the amp. The motivation for all this was to lower the noise floor enough for my MS-Pros which are a variation of the Grado RS1 (32ohm) and rather sensitive. To give you an idea of the noise level i am chasing the amp is almost silent with Sennheiser HD650's, you really have to concentrate to hear it. But with Grado 80i, MS1, 225i it becomes more and more noticeable, and with the MS-Pros it becomes distracting during quite passages and between songs. Output is set for the 4ohm tap, unbalanced.
Initial build and photo gallery can be found here --> http://bottlehead.com/smf/index.php?topic=5252.msg50648#msg50648 (http://bottlehead.com/smf/index.php?topic=5252.msg50648#msg50648)
Part 1: Glowing bottles. The general consensus is that there is little to no difference between tubes from different manufacturers. Its pretty safe to say tube rolling isn't a thing with 6DN7's. There is in my opinion one or two exceptions to that rule being the Sylvania Black Plates, and Tung-Sol tubes. Sylvanias can occasionally be found re branded under a few other labels such as International Servicemaster, Realistic International, Fivre, and Mullard.
So far i have collected sets from GE, RCA, Zenith, Fivre, National Electronics, International Servicemaster, Mullard, Tung-Sol, and Sylvania. I would go so far as to say 9/10 tubes are the same tube regardless of the manufactures stamp. The Sylvania however are clearly different in their construction, easily recognized by their cut away top support disk.
There are a few key differences in tubes so i have attached a few images to illustrate the point. Most are regular grey plates however some are black plates, and some have one grey and one black plate. And then the same three variations can be found in regular and coin base packages. You may occasionally come across tubes with an exposed heater winding on the top which are wired in series instead of in parallel, as shown in the Zenith tube below. Overall my personal preference is for the Black plate Sylvanias.
Another alternative is the 6FJ7 tube which is electrically identical to the 6DN7 but packaged in a 12pin Compactron base vs the regular 8pin Octal, as shown in the last picture. A full write up on the adapter can be found here --> http://bottlehead.com/smf/index.php?topic=5811.0 (http://bottlehead.com/smf/index.php?topic=5811.0)
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Part 2: Heater supply cap and resistor.
-Capacitor: As discussed further on in the thread doubling the capacity of the smoothing capacitor serves to half the ripple on the supply but has little to no audible or measurable effect on the noise levels of the amp. The capacitor i have used is a 22000uf Panasonic TS similar to the rest of the power supply caps, and physically the same size.
10000uf 10v - Lelon REA 85c 20% H010(M) 35mm x 18mm x 7.5mm - 2430mA
22000uf 16v - Panasonic TS-H 85c AECOS1CP223CA - 25mm x 35mm x 7.5mm - 6100ma
- .1r Resistor: My hatred for those ugly wire wound cement blocks was my motivation here to source a Dale for no other reason than its not a cement block. There are two versions of these being inductive and non-inductive, i opted for the non-inductive version.
- 100r Resistors: As suggested by PJ connecting two 100r resistors in series between the + and - terminals and grounding the center point serves to balance out the voltages on the DC side of the heater circuit. This simple modification seems to have a considerable effect in reducing background hum and is highly recommend if you are having issues. Connect one 100r resistor between terminal C1 to C3, and C2 to C3 as shown in the attached pic.
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Part 3: Voltage doubler diode upgrade. Replacing the two UF4007's with Cree CSD01060A as used in the Mainline.
I then took a snap shot of the noise at the headphone socket before/after and the difference was so small i couldn't see any difference between them. They work, and presumably better, but i really cant quantify it. As they say in motorsport, every little bit helps.
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Part 4: Headphone jack resistors / Power supply chokes,
As suggest by Doc.B adding two 120ohm resistors in series with the headphone jack greatly reduced the background noise/hum on the amp making it almost silent. Refer to heater supply 100r resistors above.
Installing the two C3X chokes in place of the 680ohm resistors in the main power supply removed the remaining 10% of background hum. Having listened to the amp at length with various headphones i cannot hear a thing, just a lovely black background which makes a world of difference to the clarity/detail. Really happy with the result ;D
Specs for the C3X are 10Henries, 50mADC, 500ohms. They both measured ~470ohms on my meter however the power supply voltages measured before/after were all within three volts of each other.
As for physical placement, it would be possible to locate them to the side of the tube sockets on standoffs but i wanted to leave a bit of room around that area to replace the two capacitors in the future. The only other place i could find was the front edge of the chassis so they sit below the headphone socket and power switch. Obviously there are no issues with hum from their placement.
For the bracket i used a piece of steel strip i had, crudely bent to shape in a vice to fit around the various components and held in place by the volume pot. I lucked out as i had a washer under the volume pot to space the knob flush with the top plate that happened to be exactly the same thickness as the steel strip so it all just fell into place. Gave the bracket a quick sand/spray with clear coat to prevent rust and called it a day.
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What is the vertical scale set to in your photo of the oscilloscope trace?
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If you absolutely must lower the noise floor even more, you can add 6dB of global feedback. It'll basically f#ck the sonic signature of the amplifier, but you'll accomplish your goal.
Swapping this part out for that part isn't going to make much of a difference. The wirewound resistor is the power supply is 0.1 Ohms and way, way out of the signal path, so mucking around with that part may appease your eyes, but it is otherwise kinda pointless. I would not at all expect the power supply chokes to lower the noise floor either.
FWIW, I'd put the UF-4007's back in. The Crees don't always do well being wired in a PTP circuit, as they have that metal tab that can cause quite some problems.
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You can go larger with the heater power capacitor. I suggest you first just parallel the ones you have on hand, to determine how important that is - doubling the capacitance should halve the ripple if it is entirely due to the heaters. If that helps, then larger caps are readily available; a 10v rating is sufficient.
Do be aware that as the tube settles in, the getter will reduce the gas in the envelope and that will reduce heater-to-cathode leakage - this is one mechanism by which letting the tubes settle may improve the situation.
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What is the vertical scale set to in your photo of the oscilloscope trace?
5mv/div
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FWIW, I'd put the UF-4007's back in. The Crees don't always do well being wired in a PTP circuit, as they have that metal tab that can cause quite some problems.
Don't worry the live backing tab was one of the first things i noticed in the datasheet, i have them well protected with heatshrink and tie wrapped to the plastic standoff for the C4S.
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You can go larger with the heater power capacitor. I suggest you first just parallel the ones you have on hand, to determine how important that is - doubling the capacitance should halve the ripple if it is entirely due to the heaters. If that helps, then larger caps are readily available; a 10v rating is sufficient.
I will try that and see what effect it has, thanks Paul.
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Btw, that trace is with the volume turned all the way down, yes? Knowing that is a 5mV/div scale, it looks like you have about 1mV pk-pk of overriding RF hash, probably from the probe cable, that is thickening the trace of the 100hz ripple. If you allow for that we are looking at about 1-1.5mv pk-pk of ripple, which translates to about .3-.5mV rms of ripple. So you are pretty much on spec for that amp.
I think the best solution for you is to use the 120 ohm series resistors at the headphone output that we have always recommended for lower impedance headphones with this amp. It will improve your signal to noise ratio.
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Btw, that trace is with the volume turned all the way down, yes?
Yes volume all the way down, but the volume level doesn't have any effect on the background noise at all. Source and headphones were also disconnected to eliminate them as sources of interference.
If you allow for that we are looking at about 1-1.5mv pk-pk of ripple, which translates to about .3-.5mV rms of ripple. So you are pretty much on spec for that amp.
Good to know, i had a feeling i was at the normal level of the amp/tubes. I am just looking to try and improve things as much as possible, open to any suggestions.
I think the best solution for you is to use the 120 ohm series resistors at the headphone output that we have always recommended for lower impedance headphones with this amp. It will improve your signal to noise ratio.
I will certainly give that a try, the wiring around the two headphone sockets is rather congested so i have to come up with an elegant way to fit them in.
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Since the headphones were unplugged that is an unloaded noise floor reading. If the headphones were plugged in it would be even lower, so the figure is definitely in the nominal range.
If you want even more quiet background for headphones, buy a Mainline. There are limits to what one can do to make a cost effective amp that will play both speakers and headphones, and Mainline does not suffer from the same constraints.
But if you just put the 120 ohm resistors in I think you will appreciate the lower noise.
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Resistors on order, will report back when i get them fitted.
I would love a Mainline but the S.E.X. kit was already a stretch for me, i was researching the Crack kit when i discovered it and got sucked in. I don't regret it at all though as i have come to the conclusion i'm a Grado man, i just cant get past that layer of disconnect with the Sennheisers so the S.E.X. amp was the right choice for me. I am really enjoying it as it does pair well with the Grados, if i can just knock the edge off the background noise it would be perfect.
In the meantime i'm going to continue enjoying it and tinker as i go, the experimentation and learning curve is all part of the fun for me. Next big purchase will be a decent DAC in the new year so i'm eagerly waiting to see what you guys come up with..
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Forgive me if I missed it, but have you installed the C4S?
I might be making this up, but I believe it helped the noise floor on my S.E.X.
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Forgive me if I missed it, but have you installed the C4S?
I might be making this up, but I believe it helped the noise floor on my S.E.X.
Hi there, C4S is indeed installed, it went in during the initial build.
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What Doc said. My amp has a massive difference in noise floor unloaded vs. connected to a good source.
I'd estimate easily 6dB, quite possibly more, in favor of the latter configuration... which is obviously the one that matters.
Even before installing those resistors, hook it up to a good source with a black background and see what happens on the scope. Extra points if you measure the noise floor of the source directly as well, so you can do a true comparison of noise added from the S.E.X. vs. noise amplified through it.
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Conversely, when you are trying to sniff out what a noise floor may be composed of with a scope you will see the most magnitude in the detail with the output unloaded. Bear in mind I am talking about gear that can be run without a load. High feedback amps and such will probably need some kind of load to remain stable.
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What Doc said. My amp has a massive difference in noise floor unloaded vs. connected to a good source.
I'd estimate easily 6dB, quite possibly more, in favor of the latter configuration... which is obviously the one that matters.
Even before installing those resistors, hook it up to a good source with a black background and see what happens on the scope. Extra points if you measure the noise floor of the source directly as well, so you can do a true comparison of noise added from the S.E.X. vs. noise amplified through it.
Double checked for sanity sake, listening to the headphones there is zero difference between no volume or full volume, or with or without external sources connected (tried two). The background hum in consistent regardless of what i do at the input stage. Its even consistent between different sets of tubes.
I haven't bothered to setup the scope to measure the various configurations or the sources, but i'm going to bet any noise measured is below the noise level of the amp which would explain why i cant hear any difference.
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I would like to know what 6dn7 tubes u have found to bbe the best sounding.n
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I would like to know what 6dn7 tubes u have found to bbe the best sounding.n
The general consensus implys there isn't any difference between them. From the limited selection i have tried i would have to agree, or if there is a difference its very subtle.
Having said that my initial impressions are as follows, RCA, GE, Zenith, National Electric, are almost identical looking inside which imply to me that they are all of the same design/origin. Without the labeling you wouldn't be able to tell the difference. Sylvanias on the other hand are a little different, and the only two i can honestly say sound a little different.
The coin base variety i have are a very similar construction to the above lot, however they have black plates and shiny silver support rods vs copper. There is something about them i just don't like, they sound lean to me or less tubey. I also believe these are the most recent manufacture of the lot. The non coin base are also black plates however they have an unusual looking spacers that set them apart visually from all the other tubes i have seen. These are my favorite for reasons i cant explain, i just keep coming back to them. I also believe these are from a fairly old stock.
Thing is, any difference i hear could just be down to age/use of the tube rather than anything else. To say for sure i would need to try multiple sets. My advice, is find the oldest tubes you can that are quite and leave it at that. I have a collection that just wont stop buzzing no matter how many hours i let them burn in, so if you have a nice quite set there really is nothing to be gained by tube swapping IMO.
For example i'm using a set of National Electronics at the moment that quietened down within a few hours use, and neither of them are micro phonic so it looks like these are the set i'm going to stick with for the foreseeable future.
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You can go larger with the heater power capacitor. I suggest you first just parallel the ones you have on hand, to determine how important that is - doubling the capacitance should halve the ripple if it is entirely due to the heaters. If that helps, then larger caps are readily available; a 10v rating is sufficient.
Do be aware that as the tube settles in, the getter will reduce the gas in the envelope and that will reduce heater-to-cathode leakage - this is one mechanism by which letting the tubes settle may improve the situation.
This was tonights fun little experiment. I am seeing ~1.2v ripple in the default config, with the 2nd 10000uf cap added i measure ~.6v, half as you said. First two scope traces 2v/div, last one is .2v/div.
With the headphones on and the amp running (probably not the best idea) i tried adding and removing the 2nd cap and it didnt make any difference to the background hum. It may make a difference, but at the moment i cant hear it over the background noise. Kind of disappointing as that would have been an easy fix.
For fun of it i had a play with PSDII and managed to get a fairly accurate model of the circuit running that gives me very close numbers to what i have measured. I then started playing around with choke/capacitor combinations and found if i replace the RC filter with a Hammond 156B placed between two 10000uf caps it will drop the ripple to .3v which has me interested. Choke specs are 1.5mH, 5A, .07ohm. Its cheap and small enough to easily mount above the speaker binding posts.
So for $2 i can add second cap and half the ripple to .6v, or spend $20 to add a choke and reduce it to .3v. That would be the curve of diminishing returns people often speak of.
Question is, what benefits would a choke have over the resistor in the power supply circuit? Is that circuit design feasible or have i got the wrong end of the stick?
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Question is, what benefits would a choke have over the resistor in the power supply circuit? Is that circuit design feasible or have i got the wrong end of the stick?
There is no question that this will not make any difference.
If you can spend 4 cents on a pair of 120 Ohm resistors, you'll get where you need to go.
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The 120ohm resistors arrived so i connected them up with jumper leads so i could switch them in/out. They do take the harsh edge of the background noise, but the majority of the hum is still present. It is an improvement, though i would rather track down the source and nip it in the bud there.
The wiring around the headphone sockets was getting too congested with little to no room to add the resistors in so i took the opportunity to replace all the wiring from the impedance switch boards to the headphone sockets. I used some triple core shielded cable i had which is a smaller gauge so it freed up a lot of room, also much tidier than having six big wires running down to the sockets.
As for the above, i suspected the heater circuit due to the 100hz frequency, and people seem to go to great lengths to quieten down these circuits with converting some amps to DC or using linear regulator circuits etc. It just struck me as being a problematic area from what i have read.
What do you recommend i try next? open to any suggestions..
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Wait a minute, i've just realized i was supposed to put those resistors in series not in parallel. DOH!
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You could rig up a temp battery supply for the heaters. See what that gets you...John
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I like your thinking, i wonder how much current a D cell battery can supply as i have four of them sitting here waiting for the quickie..hmm
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As for the above, i suspected the heater circuit due to the 100hz frequency, and people seem to go to great lengths to quieten down these circuits with converting some amps to DC or using linear regulator circuits etc. It just struck me as being a problematic area from what i have read.
People will indeed go to great lengths to quiet down a filament supply, but not a heater supply. This is why we use batteries in the Quickie and AC heating on the Crack.
Regulation comes into play when you want to build something that may get used in Japan (100V/50Hz) or the US (125V/60Hz) on the same transformer. You can use a regulator to ensure that you have 6.3V available no matter where you might be using said piece of equipment. In the BeePre, we found the regulator to be so noisy that we had to design an extra circuit to sit after the regulator to clean things up.
How did the series resistors work?
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People will indeed go to great lengths to quiet down a filament supply, but not a heater supply. This is why we use batteries in the Quickie and AC heating on the Crack.
Regulation comes into play when you want to build something that may get used in Japan (100V/50Hz) or the US (125V/60Hz) on the same transformer. You can use a regulator to ensure that you have 6.3V available no matter where you might be using said piece of equipment. In the BeePre, we found the regulator to be so noisy that we had to design an extra circuit to sit after the regulator to clean things up.
Thats a differentiation i was not aware of. Having googled it i assume you are referring to the difference between an Indirectly heated cathode, and a Directly heated cathode? 6DN7's being indirectly heated, Quickie 3S4 being directly?
How did the series resistors work?
Like a charm. I would say 90% of the hum has been subdued, the tiny bit remaining is only there when your listening for it so not a problem. I can enjoy listening to the music now without the hum causing a distraction which is great. Having to use more volume also means i am at the 12 o'clock position for normal listening which is the same as the HD650's via the XLR jack so thats a bonus.
So what effect does a series resistor have sonically? I'm almost certain it sounds slightly different but i cant put my finger on it.
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Yes, the distinction is directly heated vs. indirectly heated.
The series resistors pad the output a bit, which is very helpful for super efficient headphones, but otherwise unnecessary. The damping will be a bit different than without resistors, but being on the 4 Ohm tap already will help mitigate that.
-PB
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I think you answered your own question. With the series resistors 90% of the residual hum is removed for sensitive headphones. Thus the background is more quiet, which translates to more resolution and the increased load that the amp sees usually creates a sense of flatter, more extended frequency response. Sometimes people will consider this "less tube-like" due to a misguided assumption that tubes must always be noisy and loose in the bass.
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If anything i am feeling like some of the high end frequency are being rolled off, but i need to spend more time listening to music i know well to say for sure.
Is it worth experimenting with smaller values to find a sweet spot or is there a reason for the 120ohms value? ...tell me what to google and i'll do my homework :)
Thank again,
Mark
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The 120 Ohm resistors used to actually be a standard in the audio industry.
The high frequency response should be identical to what was there without the resistors, provided the resistors aren't abnormally inductive. (By abnormally inductive, I mean actually using an inductor instead of a resistor, lol)
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I'm pretty sure they are resistors :) Its probobly just my ears that need to recalibrate..
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Replace the transformer supply with a switching wall wart. I have not tried this in this design, but it should work. I've used this in other low noise designs with success.
1. Get one rated for the expected inrush current for the cold tubes. Designs with a medical rated version tend to be better. This current rating is so it doesn't wig out during warm up and so it runs cool in normal operation.
2. Use a series wire wound resistor in the output hot and cold to both drop the voltage, limit the surge current and to act as an RF filter.
3. Put a large cap across the filaments (indirectly heated only.) Without the series resistor, the wall wart may oscillate if you add a cap to the output.
4. Bias the filaments above ground.
5. Put grounded copper tape around the body of the wart (keep far from 115V blades) or a grounded piece of metal between the body and your circuitry for a shield. (You only really need line of site for this, if the wires and parts don't "see" the wall wart and its power cord, its usually good enough.)
6. Buy a ferrite toroid and wrap the output power lead to the wall wart 5-7 times around it (neatness counts, but don't wind so tight the copper in the lead cuts through the insulation around the lead.)
Switchers start out noisier, but they are easier to quiet down than a transformer rectifier circuit.
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Replace the transformer supply with a switching wall wart. I have not tried this in this design, but it should work. I've used this in other low noise designs with success.
1. Get one rated for the expected inrush current for the cold tubes. Designs with a medical rated version tend to be better. This current rating is so it doesn't wig out during warm up and so it runs cool in normal operation.
Interesting i thought switching power supplies in audio equipment was the work of the devil. Though my experience is limited to tiny made in China supplies that were absurdly noisy and polluted the entire house with their switching noise.
2. Use a series wire wound resistor in the output hot and cold to both drop the voltage, limit the surge current and to act as an RF filter.
Would that be part of the function of the .1ohm resistor in the existing circuit? I was reading up on the difference between inductive, non inductive resistors and different winding styles (Bifilar, Ayrton-Perry etc) to cancel out RF.
3. Put a large cap across the filaments (indirectly heated only.) Without the series resistor, the wall wart may oscillate if you add a cap to the output.
I had noticed the Mainline has tantalum caps directly on the tube socket heater pins, but figured i had asked enough stupid questions on said subject to ask..
4. Bias the filaments above ground.
Not entirely sure on what that means. I have figured out the heater supply winding is center tapped and tied to ground so it swings +/- 3v basically to lower the voltage difference from the rest of the circuit to lower noise. Or have i got that wrong?
5. Put grounded copper tape around the body of the wart (keep far from 115V blades) or a grounded piece of metal between the body and your circuitry for a shield.
Do i need a tinfoil hat to go with that?
6. Buy a ferrite toroid and wrap the output power lead to the wall wart 5-7 times around it (neatness counts, but don't wind so tight the copper in the lead cuts through the insulation around the lead.)
Funny you should mention it i was going to start a thread on mains filters to see what other people have done, advise and so on. Will do that shortly as your wisdom would be greatly appreciated..
Cheers,
Mark
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This all presumes that the noise is in fact coming through the heater of the 6DN7, and not just self noise of the tube, power supply noise, or "other".
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Replace the transformer supply with a switching wall wart. I have not tried this in this design, but it should work. I've used this in other low noise designs with success.
1. Get one rated for the expected inrush current for the cold tubes. Designs with a medical rated version tend to be better. This current rating is so it doesn't wig out during warm up and so it runs cool in normal operation.
Interesting i thought switching power supplies in audio equipment was the work of the devil. Though my experience is limited to tiny made in China supplies that were absurdly noisy and polluted the entire house with their switching noise.
** They start out noisier, but are easier than many linear regulators to make very quiet. Most of their noise issues come from common mode noise.
2. Use a series wire wound resistor in the output hot and cold to both drop the voltage, limit the surge current and to act as an RF filter.
Would that be part of the function of the .1ohm resistor in the existing circuit? I was reading up on the difference between inductive, non inductive resistors and different winding styles (Bifilar, Ayrton-Perry etc) to cancel out RF.
** I was thinking on the order of a volt or two to help limit surge currents. Normal wire wounds are fine for this application.
3. Put a large cap across the filaments (indirectly heated only.) Without the series resistor, the wall wart may oscillate if you add a cap to the output.
I had noticed the Mainline has tantalum caps directly on the tube socket heater pins, but figured i had asked enough stupid questions on said subject to ask..
** Can't speak about the Mainline, but tantalum caps don't like AC voltages and need ~2:1 voltage derating.
4. Bias the filaments above ground.
Not entirely sure on what that means. I have figured out the heater supply winding is center tapped and tied to ground so it swings +/- 3v basically to lower the voltage difference from the rest of the circuit to lower noise. Or have i got that wrong?
** I think PJ is a proponent of this. The filament is biased above the cathode voltage with a large bypass capacitor to single point ground.
5. Put grounded copper tape around the body of the wart (keep far from 115V blades) or a grounded piece of metal between the body and your circuitry for a shield.
Do i need a tinfoil hat to go with that?
** Tin foil hats are only needed if listening to DEVO.
Good wiring habits will control inductive coupling. Metal foil (copper is easy to find at craft stores) makes an easy electrostatic shield. which helps with the other "work of the devil" noise coupling method: Capacitive coupling.
6. Buy a ferrite toroid and wrap the output power lead to the wall wart 5-7 times around it (neatness counts, but don't wind so tight the copper in the lead cuts through the insulation around the lead.)
Funny you should mention it i was going to start a thread on mains filters to see what other people have done, advise and so on. Will do that shortly as your wisdom would be greatly appreciated..
** Inductance changes by the number of turns squared. Excluding problems from resonant peaks, the inductance in a noise filter usually has to double to be slightly audible. 1 to 2 turns is a big step. 4 to 6 turns is a noticeable step. 7 - 8 turns isn't that noticeable. Second order effects get to be a problem once the winding goes more than one time around the core.
Cheers,
Mark
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Cap rolling time!
Having read various capacitor roundups i kept coming back to the Russian Teflons as the best bang for your buck so they seemed like a good place to start. The Teflon varieties FT-1,FT-2, and FT-3 are only available in small capacities under 1uf so i ordered a few FT-3 .1ohm 600v samples for the interstage and burnt them in for a few weeks connected to the speaker outputs of an amplifier playing a selection of frequency sweeps, 0db sine waves, white noise, pink noise, and "How do you say Bass by Bass Mekanik" lol. It was more of a torture test really.
Installation was a bit of a challenge due to the physical size of these caps, but i found with large gauge wiring they stayed in place without moving about. I then added a cable tie to help support the weight to reduce the stress on the solder joints. The outer casing is bare metal and seems to be insulated from the capacitor but i added a layer of clear heat shrink over them anyway as a safety precaution.
Initially there was a harshness/distortion that seemed most noticeable with cymbals or notes around those frequencies, it's almost as though they are distorting but all the other instruments around it weren't. It seems this was just part of the long burn in time people say these caps need to settle down, certainly any signs of that disappeared after a week of daily use.
I have been listening to them for about three weeks now and i am still picking up little nuances that have changed. At first i found them very transparent with clearer high end and low end frequencies, but with time i have noticed a couple of things. The tone in the mid-range / low end has much more "something" i can't find the right words for. "Presence and loveliness". For example bass guitars, drums, or any other instrument in that range are much more clearly defined, it's like any piece of music i listen to now i can just concentrate on what the bass guitar is playing without it getting lost in amongst the rest of the instruments. For quite music such as acoustic or Jazz i found wood instruments, double bass or wind instruments, actually sound like wooden instruments, while bass drums/toms have a lovely presence to them. Every now and again listening to music an instrument jumps out at me in a way i have never noticed before. It's all rather fascinating.
Having re-read a few roundups i found people commonly refer to MKP capacitors are being plastic sounding, i understand exactly what they are talking about now. And the FT3 are commonly referred to as being smooth but revealing, have to agree with that too. For me the FT3 are preferred, but i can see how some people might find the greater mid/low end presence not to their liking. And they do make the overall sound very smooth sounding without losing any detail, but for some a more forward trebly presentation may be more their cup of tea. Having said that i would prefer more high end detail from the S.E.X. amp as i always found it had a very neutral presentation. The FT3s in no way reduced the high end, if anything they unveiled it a little, but it's the magic of the mid/low range is what does it for me. I am very curious to try something better in the future as the difference they have made was very surprising to me, i was expecting a more subtle change.
Next i am going to look at replacing the Solen output caps, i had a short list of candidates drawn up and then had a moment of weakness in the post holiday sales and ordered a pair of 1.5uf Mundorf Silver/Oil caps. I was really looking for something with neutral and clarity in its traits, and the silver/oil seem to fit the bill, we shall see..
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Cap rolling part II: Output caps
This is where things get a little more complicated. It has become obvious to me that i could re write what i wrote in the above post. A lot of it is still true however it has become apparent that my view of the FT3, or the role of the interstage capacitors in general was viewed through the window of the output capacitors. In other words replacing the Solen output caps has removed that restriction allowing me to see the full picture. In hindsight it would have been more enlightening to upgrade these capacitors in the opposite order starting with the output capacitors and then moving onto the interstage caps. Certainly if it wasn't such a chore to solder/unsolder them i would do exactly that out of interest. If you are thinking about cap rolling the S.E.X amp i recommend starting with the output stage as i suspect that's the stage where the greatest benefit will be found.
My choice for the output caps were 1.5uf Mundorf Supreme Silver/Oil as they have a reputation for being neutral and highly detailed. Physical size is 36mm x 42mm which as you can see i only just managed to squeeze in next to the C4S board. Anything larger would have been a problem.
So how do the Mundorf caps sound? I don't really know as i am unable to directly attribute what i am hearing to either pair of capacitors so i can only really speak of the sonic difference from my previous post with just the FT3's. In the above post i commented that i wished for more high end detail, and that some might find the mid/low end a little overly pronounced. Those comments have been rendered redundant. It is obvious to me now that what i was hearing was the limitations of the Solen output caps. The overall balance from the lowest of the low frequencies to the highest of the highs is just perfect now, i wouldn't change a thing.
I also don't find it as simple as saying there is more refinement, smoothness, clarity, or high or low frequencies. The change i am hearing is so pronounced and all encompassing all i can say is the sound is superior in every way, or perhaps i have just simply run out of audiophile vocabulary to describe it. If i had to pick just two buzz words it would be clarity and refinement, coupled with the tone and presence i experienced with the above FT3 caps.
The best analogy i can come up with is it's similar to finding that sweet spot in the middle of the room when your head is in that perfect position in relation to the speakers and four walls. Everything just comes into focus giving you the full sonic picture with all its detail and texture, that's basically the difference i am hearing. I have found that unveiling has brought me closer into the music, and consistently sucks me in well into the early hours of the morning when one more track turns into one more album. Overall the combination of these four caps have brought this amp to a whole other level, and for me well into uncharted territory that i have never experienced before.
Interestingly i have little desire to experiment any further, or upgrade any components, though it does make me wonder where you can go from here with caps like, Jensens, Deulends, Jupiter or VCaps. For the moment i am more than happy to be sucked in and wowed by this amp, even if the sleep deprivation is starting to catch up with me. And they say crack is highly addictive.. 8)
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In the SEX 2.1 (with PT-7 power transformer) the heater power is only connected to ground for two short periods during the 60Hz power line cycle - just when the diodes are conducting. Most of the time it floats. For that reason, if there is a little leakage between heater and cathode, the voltage will drift away from symmetrical. You can put a couple 100-ohm resistors in series across the DC power and ground the center point if you want to see matched voltages; you are not however going to hear a difference unless the leakage is so bad the tube should be replaced.
The center tap is grounded so that the winding itself is always grounded. This allows it to act as an electrostatic shield for other windings.
This little tip is worth adding to the thread, adding 100ohms resistors from C1&C2 to C3 creating a grounded center point helped to further reduce the harsh bzzzt noise i was hearing, and also allowed me to use sets of tubes i had previously written off as being too noisy. In my opinion this simple modification made such an effect i would suggest trying it first before experimenting with other modifications, or fitting the 120ohm resistors to the headphone socket. As always, please report your findings if you do try it...
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Have you found the source of the buzz? If you are as handy with a scope as you with assembly you could find if it is of power supply or signal path origin.
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Not really no. Its not in the audio path so its either HV supply, or heater supply. I had ruled out the heater supply as doubling the capacitance of the filter cap to 22000uf halved the ripple and made zero difference to the output noise. Having said that the above experiment creating a grounded center point on the DC side of the heater supply did make a difference so i'm not really sure what that tells us.
I cant measure the HV supply directly as my scope is limited to 400v peak to peak. I tried modeling the supply in PSUDII and experimented with difference capacitance and got some very odd results, for example doubling the first two 220uf caps to 470uf actually made the ripple worse at the end of the chain. However when i replaced the two 680ohm resistors with chokes it did reduce the output noise so i'm almost certain it is coming out of the HV supply. How to improve it further i just dont know, or maybe this is just the limit of the capability for these tubes.
The caps themselves are as good as it gets for their value and rating, i haven't found anything better than those Panasonics. I do have two 22uf Panasonics to try at the end of the chain to replace the Lelons as they have better specs, but i dont expect much if any difference. I also have a couple of 2.2uf film caps to try bypassing those but without a way to measure/quantify any difference i am going to hold off.
At the moment i have the noise floor below what is audible so i am perfectly happy with it. But if i could get it to the stage where i could do without the two 120r resistors in the output path that would be even better as i dont like the high end roll off they caused. Or maybe i just need to try another brand of resistors. The real problem is the sensitivity of my headphones, HD650's without the 120r resistors its barely audible, but with the Grados i need the resistors to hide it.
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You can make an L-pad, combining the series 120 ohm resistor with another resistor from headphone tab to ground. This reduces the signal level just the same but presents a lower impedance to the headphone. Try 47 ohms series and 22 ohms in parallel with the headphone - that will give the same attenuation as the 120 ohm resistor (assuming 32 ohm phones) but a source impedance of 15 ohms instead of 120 ohms.
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Interesting, i will give that a try.
I was thinking about what resistors to order and realized i never actually tried the amp without the 120r resistors since i installed the 100r resistors into the heater supply. As a test i made up a quick adapter cable from the XLR socket to a TRS socket to bypass them and found its perfectly fine. I had to power down my PC to reduce the ambient noise and really listen to detect any background noise with the Grados, result!
Since i had the cable made up i started switching between the TRS socket (with 120r's) and the XLR without and sure enough the SQ between them is very different. There was a good 1/4 turn of the volume knob between them making absolute a/b comparisons difficult but the conclusion i came to was the resistors make it sound what i would call more tubey. The sound had a softer, rounder edge to it and was much smoother sounding overall. Without the resistors there is a step forward in clarity and detail, and a proper sharp attack/decay to snare drums and percussion, less of the woolliness basically.
Funny thing is i like them equally as they both have their pros and cons. I'm going to use the adapter cable for a while and see which i prefer over time before i jump in and remove them permanently.
I also rolled a few other tubes into the amp and confirmed the amp was quite with multiple sets so those 100r's really do make a big difference.
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Stepped Attenuator:
I recently got my hands on a vintage Goldpoint ladder attenuator and matching balance control from eBay. The switches are dated Sept 1996 and have never been used. They are 75k items however since i have no need for a balance control i am going to rebuild it into a 100k attenuator for use in the S.E.X. amp.
Since the ladder version of the Goldpoint has been out of production for so long i did a bit of digging around in the internet archives and found a copy of the website from early 2000 with the assembly instructions. I have attached the list of resistor values from the Goldpoint site along side the values used in the Chinese attenuator i am currently using. I do prefer the look of the curves on the Goldpoint item, smoother looking and starts to raise the volume sooner than the Chinese version. Also the switch feel is much more pleasant on the Goldpoint. As soon as the resistors arrive from Mouser i will assemble and add some more pics.
If anybody knows what resistors were originally used in these i would love to know, they all have six colour codes which i had never seen before, which translates to 1% 50ppm.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fbottlehead.com%2Fsmf%2Findex.php%3Faction%3Ddlattach%3Btopic%3D2963.0%3Battach%3D5188%3Bimage&hash=04b9f5bab4ba25ff1d3d475eb448c5f5f6445aaf)
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They are 75k items however since i have no need for a balance control i am going to rebuild it into a 100k attenuator for use in the S.E.X. amp.
The 75K control will work quite well in the SEX amp, there's no need to rebuild them.
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I feel the need to warn you:
I am not aware of the Goldpoint balance control. But I have worked with balance controls that are continuous.
A balance control attenuates the left channel and leaves the right channel alone when you fade to the right channel. It does the opposite when fading to the left channel. The operation of leaving one channel alone is unusual for a dual channel device.
If Goldpoint made a switch specifically for balance it will have no positions for the two channels either side of centered.
If Goldpoint used a standard switch and just shorts all the positions either side of center you will be able to make a stereo attenuator from it.
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The 75K control will work quite well in the SEX amp, there's no need to rebuild them.
Thanks Paul, that is what i was querying the other day. The 75k attenuator i will leave as is, its only the balance control i am going to rebuild back into a volume attenuator. The dilemma i have is which will be better, the rebuilt one using modern Vishay Dale RM/CMF55's, or the original one which i think has "1%, 1/2 watt, Xicon, 50ppm, metal film" resistors.
If Goldpoint used a standard switch and just shorts all the positions either side of center you will be able to make a stereo attenuator from it.
Thanks for the heads up Grainger, that is exactly what it is, the same physical switch unit with half the resistor positions joined together.
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So you know that feeling when you hunt down a pair of nice tubes for a bargain price. That was me on Friday evening with a beer in hand unpacking a NOS pair of Sylvania Black Plates, my favorite.
These tubes turned out to be a rather unique variety i have never seen before, they have the Sylvania skinny black plate primary, but with the regular GE/RCA grey plate secondary inside a coin base package. Also the labeling on the tubes is green which i have never seen before, they are always yellow. I was really curious to hear what these oddballs sounded like.
They initially powered up fine, plugged the headphones in and had a static noise on the left channel. Hmm, tap tap, bbbzzzzzZZZZtt POP fzzzztt, and with that the heater went out and the other tube dimmed and the pilot light started flickering. I somehow managed to flick the power switch off and rip the headphones off my head without spilling the beer all over the place. Deaf in one ear and with a heart rate through the roof no less.
After i regained my composure and burnt my fingers on the tube (i do that every time), i swapped them around and powered up again without the headphones. One dead tube, and obviously still shorting out the heater supply. On closer inspection i found the issue is one of the grid support rods is making contact with the heater element, incredibly frustrating i cant get in there to do anything about it. I may have to introduce this tube to Mr Hammer and Dr Dissection in the name of science.
Thankfully the fault seem to be on the secondary side so it didn't introduce the DAC to a heater supply, and the headphones survived the ordeal too. Only permanent damage is to my hearing and nerves. I have a new rule: Always use sacrificial headphones when tube rolling, and be ready for a surprise!
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I think your new rule is prudent. My scare, documented in another thread, caused by transistor failure in the C4S board will require me to follow your rule and use a pair of cheap speakers for a few hours after I reinstall the board.
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What better way to spend a friday night than waving a soldering iron about, sad b£&*$@% that i am. I finished rebuilding the vintage Goldpoint attenuator a while back and never got around to fitting it so i had a look through my parts stash at the bits and pieces i have gathered up and figured i would throw them all in at once.
While i was switching out the attenuator i took the opportunity to replace the last of the audio path wiring from the RCA inputs to attenuator, and the short length from there to the standoffs with dual core silver plated shielded wire sourced from Navships on eBay. I've always liked his stuff, nice quality and really cheap.
Other misc bits thrown in include two new RCA input jacks, two .1% 25ppm Dale 1/2w resistors for the power supply, two Panasonic 22uf caps to replace the Lelons, and as an experiment i added two .22uf Mundorf bypass caps across them to see what happens. I did a similar experiment with my "Babybottle" quickie and was really surprised at the effect they had.
Conclusion? The Goldpoint is just lovely, instead of the clunk clunk clunk of the eBay attenuator it goes tick-a-tick-a-tick-a-tick, its just sexy. The amp also sounds different, seems much clearer with better detail in high frequencys. Then again after four cans of Heineken a speaker in a metal dust bin would sound good to me ;D
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(Tung-Sol 6DN7's)
I managed to score a pack of five NOS Tung-Sol tubes which i have been looking for since i bought this amp, they are by far the rarest of all the 6DN7 tubes. I blame Doc for this due to his comment about them sounding a bit different on the forum :P
The construction and plates are a little bit different to regular GE/RCA tubes, the first sections have black plates, the second sections have grey plates, and they have a D shape getter mounted on the side of the first section which is unique. Every other tube i have seen has had an O ring getter behind the second section.
First thing i did was plug into into my tester and measure the output, results were a bit all over the place, for five NOS tubes from the same batch i was expecting a bit more consistency. I also noticed they all measure close to the rated 40ma for the second section as per the datasheet, where as most of my Sylvanias measure higher in the 50ma range which is interesting, and has me wondering if this contributes towards my preference for them having a slightly stronger output.
So how do they sound? They have less of the midrange tubyness the Sylvanias have, or if you like they are a little less euphoric. Low end is similar, possibly more extended, but cleaner and better defined. The high end is also clearer and more extended then the Sylvanias. Overall i think they are a more balanced sounding tube vs the Sylvanias that seem to emphasize the midrange more. There is some other quality to the Tung-Sol's i haven't been able to pin point yet, they just sound a bit different, but in a good way.
As with all the 6DN7 varietys were not talking a night & day difference, its more subtle to the extent it takes a pair of headphones and some careful listening to pin down the differences. Having said that i would confidently take the Pepsi challenge on GE/RCA vs a pair of Sylvanias or Tung-Sols, the difference is enough to be able to single them out, and enough to make them worth seeking out.
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I agree with you, the Tung Sol's sound good but very similar to everything else out there. My pair was a gift from a fellow Bottlehead and I leave them in not out of their sound but to honor the gift. The 6DN7 lasts forever in this amp!
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I've started my build and am following recommendations here - nice build by the way!
Is there a range that is acceptable to the 100r Resistors to be put in the heater circuit? I've got quite the pile of resistors but none (other than some monster 12w Mills that are not going to fit) that are 100r. Recommeded wattage range?
Thanks!
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Good question, and i don't really know the answer as that as the value was recommended by PJ.
From what i understand using lower value resistors will center the voltages more accurately, but at the expense of using more current and dissipating more heat. I dont know how to calculate the current across the resistors, and therefore the wattage rating needed so hopefully one of the BH guys will chime in and educate us...
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Ohms law works pretty well.
6.3V with 200 Ohms across it.
P=(V^2)/R
To keep temperature reasonable, triple that power to get your resistor wattage rating.
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See, you always make it sound so simple :)
In that case i get a little under .2w with 100r's so a quarter watt resistor isn't going to cut it, unless you jump upto 200r's in which case your down to ~.1watt. Got it.
Thanks Paul!
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To keep temperature reasonable, triple that power to get your resistor wattage rating.
In that case i get a little under .2w with 100r's so a quarter watt resistor isn't going to cut it, unless you jump upto 200r's in which case your down to ~.1watt. Got it.
.2W of dissipation means 1/2 Watt minimum resistor size, but more likely a 1W part.
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Thanks gents! 'preciate the info. I can sling solder around with the best of 'em but my electronic knowledge is on the level of what a dog knows about brain surgery.
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Hi,
The RESISTOR that will be for C1 to C3 and C2 to C3 to reduced the noise can i use any type of 100R 1/2W or do you have any recommendations?
Thank You!
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Any metal film will do the job, whatever you can get.
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Any metal film will do the job, whatever you can get.
THANK YOU!
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I finished replacing the 0R1 5W resistor that i screwed up while i was installing the 2 100R on C1 and C2.The reisistor mod works,No hum with the Q7X1/DT8XX 600R and HD6XX but i still have slight HUM when using a 24 ohms headphone.I'am thinking of installing a CHOKE will this MOD help to lower the HUM?
THANKS!
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i still have slight HUM when using a 24 ohms headphone.
Are you using the 4 Ohm taps on the output transformers?
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Oops!I forgot about that 4ohm tap.No i used 8 ohm tap i will try the 4 ohm tap.
THANK YOU!
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Sad to say the hum still there,The 4 ohm tap is quieter than 8 ohm tap.THANKS!
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What are the 24 ohms headphones you are using? Interested to see what kind of sensitivity they have, for example IEM's just aren't going to fly.
The chokes can help a bit, but nowhere near as much as the resistor mod for eradicating hum. The chokes seem to me more effective at higher frequency's to lower the noise floor and give a blacker background. I cant really recommend them as a cure for hum due to the cost and hassle of trying to mount them.
I made many small tweaks which all helped in there own small way to quieten down the amp, i believe replacing the audio path input/output wiring helped greatly in that area. Its hard for me to say really as i did a mini rebuild and replaced so many components and bits of wiring at once i cant single out the difference each made. It is also entirely possible you just have a slightly noisy set of tubes, is the hum the same on both channels? and does it move if you switch the tubes around?
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I used Sony XB700 and Audio-Technica M30 with XB700 it's more hum than with M30 even with 4R tap still humming but it's very very low you really need to listened to it.My wife and my kid can't hear the hum until i told them so it's not bad at all and it's not affected by the volume pot so that is the good thing.It is dead quiet with Q701,DT880 600R and the HD650 the resistor MOD helps a lot to reduced the HUM.I can even used the 32R tap with higher impedance HP with very little HUM.It only bugs me because i was the one who build it and know that the hum is there other than that if don't let anyone know about the hum while they are listening to it they would not noticed.For the CHOKE i'am still planning to put a pair for $12 a piece it's not bad the only thing is where to mount it.
THANKS!
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Sony 106 (dB/mW) 24 ohm
Audio Technica 100 (dB/mW) 65 ohm
Those Sonys are sensitive alright. The Chokes may well give you that little edge you need, provided what you are hearing is coming from the HV supply. Just keep in mind placment of the chokes is critical so they dont pickup, or interfere with any other iron inside the chassis. I found the position i am using worked really well in that regard, which is just as well as i really didnt have any other options that would fit inside the wood base.
Not sure how up to date the thread pics are so here are a few pics of the current layout, getting the soldering iron in to mount the caps was a real challenge!
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Yeah i don't think if i can install the choke that way.
I will be upgrading the 1.5uf and the 0.1 caps next week so i will see if i can move stuff around to accommodate the choke.
(http://)http://cdn.head-fi.org/0/0f/200x200px-ZC-0f5f840a_DSC_3474.jpeg
THANKS!
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I cant really make it out, did you leave the original 1.5uf caps in there too or?
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Yes the original 1.5 still there i will be replacing it with a 1.5 Mundorf.The big 2 caps is the replacement for the 22uf.
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Novelty Caps: Gudeman paper in oil
When i found these oddballs on eBay i just had to have them. They are a paper in oil construction housed inside a hermetically sealed glass enclosure, rated at .1uf 5000vdc. I've had these on my desk for a few months which provided constant amusement watching the air pocket slowly move around inside the glass, and i mean slow as it takes hours for anything to happen. I don’t know why but i found that oddly amusing.
I have no idea what these were originally intended for as there cant be too many applications requiring 4-5kv rated caps. I haven’t been able to find very much information about Gudeman as a company other than they were based out of Chicago Illinois and produced a whole range of paper/oil caps around the 1950's and 60's. They also seem very popular with the vintage Guitar community in tone circuitry, but little to no information was found regarding these glass cased high voltage caps.
On my capacitor testers both of these measure exactly .1uf and have no leakage up to 450v dc so they are still perfectly healthy. With that in mind i removed the Russian Teflon FT-3's from my S.E.X. amp to see how they perform. My expectation going from a Teflon capacitor to a Paper/Oil was a rolled off high end, and a thicker sounding presentation through the midrange. Certainly that has been my experience in the past with different Russian PIO flavors. That is not really what i found at all, there is an almost imperceptible difference in high end detail vs the teflons, the midrange is very similar with maybe a tiny bit more warmth and smoothing, and a noticeably less rolled off low end. I was expecting this to be a quick experiment before i soldered the FT3's back in but instead i found myself sitting up straight and paying attention.
The first big difference i have noticed is how much energy there is dynamically making the FT3's sound thin and weak in comparison. Movies with a recorded low frequency effects sound channel "LFE" have real powerful energy behind them now. Its not a case of an over emphasized or overpowering low end, but more a realization of how much of the impact i was missing before. If a kick drum goes thump, it goes thump!, not a bump.
The other big difference, and the one that has surprised me the most is its almost holographic presentation of the music. If you have ever heard a binaural recording where the soundstage has moved outside your expected boundaries to the point of startling you, that is kind of what i am experiencing. I have been listening to these caps for days now with different headphones and music and i still can’t wrap my head around what i am hearing, there are layers and depth of instrument separation and positioning that just wasn’t there before. I just can’t seem to rationalize it which is driving me nuts, but on the other hand i have been rediscovering my entire music collection again and loving it.
Is it possible the FT-3's aren’t really as good as everybody makes them out to be? or have i just stumbled across something rather special? or gone a little insane?
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I put a pair of these, 8kV rated, in the power supply for my electrostatic speakers; in the power supply. Mine were bright red.
Of course, they never gave a moment's problem. The cheap mica caps that Infinity put in parallel/series to double the voltage rating were very unreliable. That is less than a dollar for the caps in a $2000 speaker system. Cheap asses! Bottlehead wouldn't do that.
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Interesting, they say with most audio equipment you are listening to the power supply, i suppose the same is also true for electrostatic speakers. They sound like an interesting pair of speakers, i thought you were using a full Blumenstein setup?
I am still deeply impressed with these capacitors. I also picked up a pair of Jupiter paper/wax .1uf 600v caps for a steal recently so they should make for an interesting comparison. I am a little concerned about the chassis heat despite the fact they have the same temperature rating as the Mundorfs of 70c. More as it happens..
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The Servo-Static I was an interesting speaker. It was electrostatic from 100 Hz up. It had the first commercial subwoofer with motional feedback. It came with a three way crossover/servo sub amplifier. It took two more power amps to run them.
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Motional feedback is an interesting concept i had never heard of before, complex looking circuitry mind you!
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It is old. Many, maybe most, of the subs marketed for high end audio today use some feedback from the cone to the amp to correct its motion. It is so widely used that it is hardly mentioned.
The SS-1 came out in 1969.
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Fancy Caps: Jupiter HT Paper BeesWax .1uf 600v
HT are the "High Temperature" range suitable for valve amps. I have heard of potential issues with these failing due to heat, but they are rated for 70c which happens to be the same as the Mundorf Silver Oil range i am using in the output stage. They do have to endure 30-40c inside the S.E.X. amp so time will tell how well they last.
Manufacturers blurb: A unique blend of the old sound with refinements of the new. New high temp (HT) series replaces the original beeswax/paper design (3rd generation design). Jupiter Condenser HT line of capacitors feature a reinforced beeswax paper dielectric and (with further improved impregnation techniques) is now cased in a non-drip/melt casing and can withstand higher operating temperatures. Perfect for DIY and OEM use where natural sound is demanded.
The "new look" to Jupiter Condenser Co. capacitors, is true to form following function. Not just a new style, the outer casing is still true to natural materials yet offers improved environmental characteristics. A paper tube impregnated with phenolic resin assures excellent moisture resistance along with a resin end fill to lock moisture out. The casing material will not melt or drip even at higher temperatures.
For productions, a computer controlled wax vacuum impregnation system was engineered and built by Jupiter Condenser, and section processing is based on techniques developed by Western Electric and RCA. This is capable of deep vacuum and high pressure, providing consistent impregnation with more gas and moisture removal. New proprietary measures of strengthening dielectric properties have been developed and employed which yield higher insulation resistance and allow greater operating temperatures. Wax and paper construction yields a very well mechanically damped capacitor, free from electrostatic and mechanical ringing.
Specifications:
Tolerance ±5% standard
Rated voltage 600Vdc - Tested at 1200VDC at two stages of production
Pure silver leadouts 20 AWG (0.812mm dia.)
Max temperature +70°C
Beeswax impregnated Paper dielectric
Aluminum Foil electrode material
Normally i wouldn't have considered a "premium" capacitor such as these but i managed to pick up these two for less than half their retail price, an offer too good to pass up. They are clearly superior to the FT-3's so a side by side comparison is a bit pointless, vs the Gudeman oils however there is less of a difference. The two are very similar but i would have to say the Gudemans have a larger, bigger sound to me. i.e. more dynamic, and energetic sounding. The Jupiters are a little bit more restrained, but have better tone/detail and a clearer high end. I have switched between the two twice at this stage and still cant make up my mind which to keep in there. Gudemans are more fun, but i suspect the Jupiters are technically more correct if that makes sense.
Are they worth the premium price new? They are listed for @£22 or $33 each so if that doesn't scare you off then i can highly recommend them. They are also tiny at 14x25mm!
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I have had Jupiter HT caps in my S.E.X. amp for years with no problems. My amp runs almost every day for several hours at a time - 8 hours today. I have had no problems in that time so I dont think you will have heat related problems either. I have a pair of 0.1uF caps in the interstage or coupling position and a pair of 2.0 uF output caps since I have the Magnequest full nickle output transformers installed on my 2.0 version of the amp. I like the Jupitor caps so much I have never wanted to replace them. Although the new copper foil caps are tempting me...
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The original Jupiter caps, in the v2.0 SEX amp (without the ventilation holes in the top plate) has some incidents of melting wax and internal short circuits. I don't think we've heard of any such problems with the new, higher temp versions. Nevertheless, being a conservative engineer, I recommend parts rated 85 degrees C or more. I like my safety margins.
That said, the Jupiters I've heard sound pretty darn good.
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That's good to know, thanks folks. I also have a pair of 2uf HT's that i was going to install into the S.E.X but decided to keep those for my speaker preamp instead.
Its funny how premium grade capacitors like Mundorfs and Jupiters always seemed a little excessive to me until i actually tried them, now they seem great value :)
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Reporting in...
I placed two 1/4 watt 100R resistors from C1 to C3 and C2 to C3, I could hear a hum before with my HD650's on the 4ohm taps... It's gone now, for me. :)
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Result!, thanks for reporting back :)
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I would like to install the resistors from C1 to C3 and C2 to C3 during the initial build. Right now I'm at the input wiring part. What step would you install them, and would there be any notes like attach but don't solder just yet?
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Page 21, the paragraph
( ) Using the end stripped back 5/8â€, insert the black
wire into the bottom hole of terminal C1, from the back
side of the strip. Insert the red wire into the bottom hole
of C2. Solder C1L and C2L.
Just before soldering those two wires i would add in the resistors to C1L, C2L, and C3L, BUT i highly recommend you build the amp completely stock first because if you do have any issues those will only complicate matters and make it harder to troubleshoot. They may also give you different readings for the resistance and voltage checks from what is in the manual.
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good point... Normally I always build a bottlehead kit in stock form first. It's just that it looks like it's hard to add them in afterwards. I've already passed that step I think so I guess They'll go in later if need be
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What is the equivalent of the C3X from Hammond(Patrsconnexion)?
Thanks!
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What is the equivalent of the C3X from Hammond(Patrsconnexion)?
Thanks!
157H is pretty close.
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The current production C-3X may actually be made by Hammond.
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THANK YOU!
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Latest experiment (eXperiment is in the name after all) was to replace the bias resistor in the driver stage with a resistor/LED string. I had a couple of nice precision Dale 499r resistors that i used in the C4S, and a couple of HLMP6000's in stock so there really was no excuse not to try it.
If i worked it out correctly the manual states ~2.5v bias which implys to me the operating point is around 2ma. On that basis a 499r resistor would give a bias of .98v, plus the 1.55v of the HLMP should give ~2.5v combined. In practice i was seeing ~2.2-2.3v before the mod, and approx .2v higher on each side after the mod. Good enough.
Now for the hard bit, does it sound any different? I could convince myself it sounds cleaner and more in focus. But that's probably because that is what i am expecting it to do. Kind of kicking myself i didn't take some frequency response and distortion measurements with RMAA before hand. Either way it cost peanuts, and i dont fancy playing a game of operation trying to get the soldering iron back in there without melting something so they will just have to stay :)
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I feel the same way about a number of minor mods. Taking them out is harder than putting them in. If it didn't harm the sound they stay.
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You can use a TL431 or LM431 to get 2.5V of bias, much like an LED. The middle leg goes to ground, and the two outside legs go to the tube's cathode. (The Stereomour uses this)
-PB
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Interesting, i see in the Fairchild datasheet they have a graph for dynamic impedance showing a flat line of .2ohm up past 40Khz. I assume it outperforms the HLMP if you are using it in the higher end kits?
Also have you ever taken any measurements of the S.E.X. amp? I've started using RMAA and i'm not 100% sure of the accuracy of my plots. Its telling me around .3 to .4% THD, but the frequency response seems a little odd, large hump at the very low end and starts to roll off the high end sooner than i expected.
Cheers,
Mark
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That looks about right to me - my design target for the output transformer was 40kHz at -3dB, which is -1dB at 20kHz. I can get much better numbers but it would not sound as good for other reasons.
A 1dB peak at 20Hz is reasonable for a parafeed output. It will change depending on the spaeker mpedance - did you load the output with a resistor?
Yes, I'm still on vacation in France, but nursing a cold and bored in the apartment so I'm checking the forum ...
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Thats good to know, thanks Paul. The testing was done through a Pete Millett sound card interface so i'm not sure what the input impedance is, i think its around 600ohms. I re ran the tests into 300r and 32r loads and the 32r load does indeed flatten the low end spike, but also doubles the distortion figure. I assume that is to be expected being a more difficult load to drive. The 300r load is pretty much identical to going straight into the interface, which implies the interface is 300r or higher.
I switched out the HLMP/500r string with LM431's as per Paul B's suggestion and the high end frequency response jumped up to pretty much exactly what you specified, -1db at 20khz on the money.
Initially i only changed the left side of the amp and noticed the difference when i compared the left/right channel response. I then changed the right side to an LM431 and the frequency response jumped up there too so its 100% the difference between the two bias setups and not some random change in my testing setup. I'm tempted to solder the stock resistor back in now and measure it out of curiosity :)
I debated about where to install the 431's as the free positions on the C4S board were very tempting, but in the end the added lengths of wiring from the socket to board swayed me into soldering directly onto the tube socket. Lead lengths were a perfect fit too.
Thanks again guys!
P.S. Get well soon PJ, such a shame to have the sniffles when you are surrounded with nice wines. ...assuming you drink.
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Bonus Content: Tung-Sol vs Sylvania Black Plates
Found this rather interesting, Sylvanias seem to have a slightly flatter low end response, but roll off the high end slightly sooner. They also measure lower distortion figures too. I have attached both 32ohm and 300ohm load plots.
Obviously take all the results with a pinch of salt as results may vary from tube to tube. I dont know how many hours of use the Tung-Sols have, its probably close to six months since i got them. The Sylvanias were fresh out of the box, pretty sure i have never used them. Its still interesting all the same...
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Found a problem, having just plugged in some headphones i now have a hiss on both channels, i can only assume the LM431's are creating the noise. Have you experienced this Paul, or is there a specific model of the 431 i should be using? Failing that i may have to go back to the LED/Resistor string.
Cheers,
Mark
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We did once get a bad batch of "431" chips - they may have been fakes, or factory rejects - that were very noisy. Hard choices there - resistor/capacitor is always quietbut you can hear the cap, resistor alone risks high frequency drive to the power triode, LEDs can be noisy (the predecessor of theHLMP-6000 was measured to be very quiet - but long ago), chip regulators such as the 431 can be noisy (the specs on the major brands say they should be relatively quiet, but fakes and rejects abound) ..
Thanks for the kind words guys, feeling much better now - I'll probably be pretty occasional on the forum over the next few weeks!
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I did a little research and found a few sources who claim the On Semi LM431A measures the quietest so i ordered a few different brands from Mouser to see. Using the highly scientific testing methodology of a pair of Grado RS1 headphones on my head i found the TL431's were actually considerably quieter than the On Semi, Fairchild, and Ti LM431's. Unfortunately it still wasn't good enough with a constant white noise in the background.
I found some test measurements which noted the LM431 performed much quieter when set for higher voltages, i assume that is due to the resistor added between the reference and cathode. The test report measured the LM431 noise in the 20uv range, when configured to 5v it measured down around 3uv, vs a selection of red LED's that all measured under 1uv. It seems to me that adding the two resistors across the 431 would defeat the purpose of using the 431 in the first place, and similarly adding bypass caps would do the same so i came to the conclusion it just wasn't going work and threw in the towel. Frustrating really as there was clearly better high frequency response and lower distortion while using it.
So back to the HLMP/500r sting, i did one final frequency response plot with the stock 1.27k resistor and sure enough the HLMP helps the high end response. Its kind of a half way point between the stock resistor and LM431, but more importantly its completely silent.
Before i close the door on the LM431 idea i should point out i am using very sensitive Grado headphones, the noise may not be audible with less sensitive headphones or speakers so it may work perfectly fine in other setups. As always, please report your findings ;)
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I have been following this thread like trial and error gospel ever since I submitted my order for the sex 2.1, great job to all who contribute and especially mcandmar for sharing all the fun with us!
My kit and c4s kit should be arriving within a couple of weeks and I've already gathered some mundorf Supremes (2.2uf, and 0.1uf for parafeed and interstate caps respectively), two triad chokes, some 100r resistors for heater supply, and all I'm waiting on now is for my mind to finish an internal debate over a goldpoint or this; http://www.diyaudioblog.com/2011/03/elma-stepped-attenuator-populated-with.html?m=1
Anyway I plan to build the kit entirely stock (except for the attenuator just to make wiring it up easier). Almost all of my listening will be with Alpha Dogs headphones and a set of speakers I'm building with my father's friend (the speakers are rated 8 ohm too I believe, maybe 4 though).
First question, if anyone has experience with any of the Fostex mods, ZMF or MrSpeakers Mad Dogs, etc. should I wire for 8 or 4 ohms? Any help would be greatly appreciated. I'm leaning towards 8.
Second question:
In what order should I implement the upgrades and modifications if I wish to enjoy each individual change as much as possible? Would putting the c4s in first only make all the changes brought by capacitors that much more transparent, or does it have an opposite effect?
Thanks for reading guys!
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Glad to be of help, sorry about your wallet :)
I would start with 8ohms, i've stuck with that for a variety of different headphones, and since your planning on driving speakers that would make 8ohms an ideal setting.
As always, build it stock first, then move onto the Bottlehead options, impedance switch boards, then the C4S. Basically you want to get all that up and running before you start adding in custom parts to the mix.
As for the upgrades, the capacitors will give you the most immediate change, but i would would fit them last as they limit access to the rest of the circuit around them and its all too easy to ruin a nice cap by hitting a hot soldering iron against it.
Also resist the urge to chuck all the parts in at once, best to use it for a while so you can fully appreciate the differences each change will make. Enjoy, and keep us posted!
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Glad to be of help, sorry about your wallet :)
I would start with 8ohms, i've stuck with that for a variety of different headphones, and since your planning on driving speakers that would make 8ohms an ideal setting.
As always, build it stock first, then move onto the Bottlehead options, impedance switch boards, then the C4S. Basically you want to get all that up and running before you start adding in custom parts to the mix.
As for the upgrades, the capacitors will give you the most immediate change, but i would would fit them last as they limit access to the rest of the circuit around them and its all too easy to ruin a nice cap by hitting a hot soldering iron against it.
Also resist the urge to chuck all the parts in at once, best to use it for a while so you can fully appreciate the differences each change will make. Enjoy, and keep us posted!
I never really shared any pics of my old Crack's internals, I can definitely work with tight spaces after stuffing that headphone amp! :D
I attached some different shots of it between mods, without the capacitors mounted with zip ties of course, much neater in the box. Mounting the choke at an angle to the transformer resulted in absolutely zero hum. Dunno, I tried to follow my Morgan Jones amplifier design text to lead me. For my first time with a soldering iron since my freshman HS electronics course (22 now) I think I did a decent job with the crack. Now time to move on and keep improving.
Planning a much cleaner build this time; starting with the wooden base. An extremely light burgundy stain followed by a linseed oil finish, cream white top plate (if I can find a powder coated to do it) with claret/red wine accents to match my Alpha Dogs. Will definitely have to try to make a thread 1/100th as useful as yours!
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Generally any change that increases resolution (i.e. most of the good ones) will make the next change easier to hear. So the optimal strategy in my mind is to go with the biggest effect first, so that the more questionable "upgrades" get the best chance of making a difference.
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Generally any change that increases resolution (i.e. most of the good ones) will make the next change easier to hear. So the optimal strategy in my mind is to go with the biggest effect first, so that the more questionable "upgrades" get the best chance of making a difference.
I think I'll 'fit' the larger mundorf Supremes just to make sure the c4s board won't cause issues and/or how to solve potential issues, then I'll build it stock, add c4s, then solder in the Supremes where I previously fitted them.
Thanks everyone! Best support community by far.
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Has anyone here ever used an Elma attenuator? Have a line on one populated with kiwame resistors but it's 50k. Will there be any issues with that? My source will be a Schiit Modi 2 uber
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Elma make the switching part, for example the Goldpoint attenuators use the Elma switches, but add their own PCB's and resistor layouts to make the complete attenuator. Anything using Elma switches gets a thumbs up from me.
There are different types of attenuator, main ones being series and ladder. Personally i don't like the idea of series attenuators as you end up with a whole string of resistors in the signal path, where as with ladder style there is only ever two resistors in the path creating a divider. Easy to spot the difference as the ladder style have double the amount of resistors.
Then there are resistor choices, much like brands of coffee or beer everybody will have a preference. Kiwami are carbon resistors, i think they are carbon film as opposed to carbon comp. Personally i find them a little soft sounding, rounds the edges off and makes things all smooth and cuddly. Where as metal film i find to be more transparent so you don't notice them. I've always use Dale RN series resistors in signal paths and attenuators for that reason, but again that's just my opinion, i may be completely wrong about that.
I believe 50k will work fine, especially with something like a Modi driving it as it will have been designed to drive 20k-50k loads.
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Thanks. It's an Elma switch populated with thru hole kiwames. The slight soft sound, or rounding off shouldn't be an issue because I tend towards neutral-bright sound preference.
The attenuator in question:
http://www.diyaudioblog.com/2011/03/elma-stepped-attenuator-populated-with.html?m=1
Thanks again!
Still part of me wonders if the series goldpoint with and resistors for under $180 shipped is the better choice.
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Dunno. Depends on how much you are getting the Kiwami one for. From what i have read many people dont like the SMD resistor versions of the Goldpoint, i remember Doc B expressing a dislike for them too so stick to through hole resistor attenuators.
Personally i think these are the best value, proper ladder style unlike the current Goldpoints and uses Dale resistors. http://www.ebay.co.uk/itm/assembled-dale-24-step-copper-axis-attenuator-volume-control-100k/281664997434?hash=item41948ac83a (http://www.ebay.co.uk/itm/assembled-dale-24-step-copper-axis-attenuator-volume-control-100k/281664997434?hash=item41948ac83a)
You can also buy them unassembled if you are a sucker for punishment. BTDT, and swore never again.
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Ladder attenuators keep a constant impedance to the source. It approximates a pot with none of the drawbacks of a pot.
I, personally, would not consider any other configuration.
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Dunno. Depends on how much you are getting the Kiwami one for. From what i have read many people dont like the SMD resistor versions of the Goldpoint, i remember Doc B expressing a dislike for them too so stick to through hole resistor attenuators.
Personally i think these are the best value, proper ladder style unlike the current Goldpoints and uses Dale resistors. http://www.ebay.co.uk/itm/assembled-dale-24-step-copper-axis-attenuator-volume-control-100k/281664997434?hash=item41948ac83a (http://www.ebay.co.uk/itm/assembled-dale-24-step-copper-axis-attenuator-volume-control-100k/281664997434?hash=item41948ac83a)
You can also buy them unassembled if you are a sucker for punishment. BTDT, and swore never again.
Biggest issue with that is the ship time can be horrible. I'd hate to have the kit arrive next week sometime and then I spend a month waiting for the Dale resistor ladder attenuator because I have looked at that one.
Anyone have any extras? ;)
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What is the necessary wattage rating for the 100r heater supply mod? 1/2 watt?
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Yes at a minimum as they will be dissipating approx .4watt.
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Then a one or two watt would be nice to keep the heat down. heat is an enemy to all components.
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Then a one or two watt would be nice to keep the heat down. heat is an enemy to all components.
My thoughts exactly.
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For those who have installed the c4s, would it be beneficial for me to install the nylon standoff before I populate the terminal strip? It looks like it'll be a tight fit, removing the nut among the diodes, wires and resistors, and If it saves me from a later hassle then it's worth it.
Thanks for reading!
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It is easier. You might also get some soldering iron burns on the standoffs while installing components. Those burns won't compromise the standoff it will just look bad.
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It is easier. You might also get some soldering iron burns on the standoffs while installing components. Those burns won't compromise the standoff it will just look bad.
Well we don't build amps to stare at standoffs :P
Thank you Grainger!
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To infinity and beyond!
Although this isn’t specifically related to the S.E.X. amp i thought it worth sharing all the same. For those unfamiliar with LDR attenuators they use optical couplers (specifically light dependent optocouplers) as voltage controlled variable resistors to mimic the function of a potentiometer. In theory they are more transparent and have a lower noise floor than either a carbon based pot, or resistor based stepped attenuator. Curious yet? ...me too ;)
The specific type of optocouplers used are Silonex NSL-32SR2 which have an unfortunate property in that they vary hugely in their response from sample to sample. They are so horribly matched you have to buy at least two dozen of them and painstakingly measure each one with a fixed current to find a couple of matched pairs. In an ideal world you want four matched, but you can make do with two sets of matched pairs. Most resistors have a tolerance of 1% to 5%, these have a tolerance more like 50%, but once you find a set that measure the same your set. They don’t have to be exactly the same as the final balance between them can be balanced out with trim pots, but the closer the match the better.
Parts required:
-x4 NSL-32SR2
-x4 100ohm resistors (current limiters to LDR’s)
-x2 1k trimpots (to balance left/right channels)
-x1 100k linear volume pot (adjusts voltage to LDR’s)
And that’s it. Only other catch is you need a quiet 5v DC supply for them, a simple 7805 or LM317 voltage regulator is perfectly adequate. The current draw of the entire circuit is very small, under 100ma so you can get away with tapping into a 6.3v ac winding and rectify into DC which will give you ~7-8v to feed into your voltage regulator for a clean 5V DC output.
Once you have recovered from spending hours slaving away at a breadboard with a multimeter matching sets you then have to assemble the circuit and do one final balance with the trim pots to get each channels response exactly the same. I almost forgot to mention the second catch, the resistance values vary wildly with temperature so they need to be running for about half an hour before they settle down. Just holding one of the LDR’s between your fingers will change its resistance enough for the volume change to be audible within a few seconds. Kind of amusing in some ways, but it does make their suitability for the inside a hot valve amp questionable.
The how does it sound question. In my test circuit i went from a regular 100k carbon pot so there was a noticeable improvement in clarity, better defined bottom end, and cleaner sounding treble. I then switched to an eBay ladder attenuator with Dale resistors and honestly, i couldn’t really tell any difference. Possible the LDR was a bit more detailed in the high end, but its vary hard to say when it takes 5mins with a soldering iron to switch between them so i’ll keep experimenting with it and see how it performs over time.
Overall conclusion. Huge variation between samples means you have to buy them by the dozen at a time. Hard to find, i could only find them stocked in the US so they cost me more in shipping than for the parts. Pain in the arse to match. Require a dedicated power supply to drive them. Huge drift with temperature. Pain in the arse to match.
On the plus side the entire board is compact, i fitted the entire circuit with AC to DC power supply on a 3†x 1†protoboard. The actual volume control action is nice as they react slowly to change so any volume adjustment has a fluid gradual change. A novelty when you’re used to stepped attenuators. Possibly sounds better than a ladder attenuator, jury is still out on that one. Unless i come to the conclusion there is a tangible improvement sonically over stepped attenuators i’m going to say that they are more trouble than they are worth. Nice idea, but a pain in the arse to implement.
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Lightspeed Part II: LDR attenuator vs regular carbon pot
I found this rather surprising, not so much the difference between them, but how much high end gets lost in a cheap carbon pot to begin with. The actual volume levels were slightly different between them but it clearly illustrates the differences all the same.
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I am guessing that the difference is due to the lower impedance level of the LDR, interacting with the Miller capacitance of the input tube. The LDR loss is mostly the natural rolloff of the output transformer.
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Although its not a S.E.X. amp the transformers happen to be a pair of OT-2's, and perform very well to my ears ;)
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Oh yeah, I see. So what is the input tube (is it a tube?) and where is the volume control set when doing this measurement? Just curious is all.
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Its a project i'm working on inspired by Docs old rack mounted headphone amp. Using two Salas SSHV2 shunt regulators into 6C45 tubes with CCS plate loads. My original aim was to get a pair of TL-404's, but when i found the OT-2's i snapped them up to get it all up and running. Its still work in progress, but has surprised me so far with how well they work in the circuit.
Not too sure about the actual volume level, RMAA outputs a 1vrms signal and you set the level so the returning input signal is as close as possible to -1db. I think i was down to about -3 to -4db to stay below clipping. The test was run with the outputs wired with 1-8 linked / 2-7 linked into a 32ohm load.
I still havent got my head around the math to work out the theoretical coupling cap size, i still don't think its right as something sounds a bit off. From testing with RMAA i think the answer is ~8uf. 5-6uf seemed to give me a large hump at the low end similar to my S.E.X. amp, where as 10uf and 12uf starts to roll off the low end which i wasnt expecting. More testing needed... :)
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Thanks for the info - this helps.
First off, the 6C45 has a large Miller capacitance, which may explain a sensitivity to high impedances. (In the headphone amp, if I remember right, we used a step-down transformer at the input, 10:600 ohms, followed by 600-ohm attenuators.)
For the parafeed cap, I think in the end you'll have to do listening tests. Without the stabilizing effect of the plate choke's inductance, the LF tuning varies with signal level - specifically, the transformer's inductance. Plus, the core losses become important enough that it's really something between a choke and a resistor. A theoretical analysis is not THAT difficult, but the level dependence means you must compromise between large and small signal performance. So you do listening tests - no other way to answer that question.
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I would also chime in that a lot of the love for LDR's may come from the high-ish distortion that they produce when used. This could be a very, very good thing for an overly aggressive solid state amp, but might be a little too much ahead of a SEX amp.
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Thanks for the info - this helps.
First off, the 6C45 has a large Miller capacitance, which may explain a sensitivity to high impedances.
Turns out the LDRs impedance is in the 15-20k range which may explain the large discrepancy between the 100k pot. If i got the numbers right i get ~110pf capacitance, so with the 100k pot that would give a roll off at 14.4khz, vs 72khz with a 20k pot. I'm going to try and find a lower value carbon pot to test with and see if that theory plays out in the real world.
For the parafeed cap, I think in the end you'll have to do listening tests. Without the stabilizing effect of the plate choke's inductance, the LF tuning varies with signal level - specifically, the transformer's inductance. Plus, the core losses become important enough that it's really something between a choke and a resistor. A theoretical analysis is not THAT difficult, but the level dependence means you must compromise between large and small signal performance. So you do listening tests - no other way to answer that question.
Any formulas i have found assume the circuit uses a plate choke, i cant find any equivalent for use with a CCS plate load. I have deliberately been testing into a 32ohm load to match my headphones, but i'll have a look at the signal level at normal listening volumes and start testing around that point. I have found a very nice pair of 10uf PIO caps which may bias my decision a tiny bit.
I would also chime in that a lot of the love for LDR's may come from the high-ish distortion that they produce when used. This could be a very, very good thing for an overly aggressive solid state amp, but might be a little too much ahead of a SEX amp.
And PB chucks a spanner into the works :) That's not something i have heard mentioned from the evangelists, if anything they claim the opposite. I'll see if i can measure any difference between it and a ladder attenuator as i have a nice Goldpoint stashed away somewhere.
Cheers all....
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Anyone experiment with CCS resistors? I have a couple Vishay 500 ohm s102 bulk foils to try out when I finish my build stock, then add the c4s. What about the 150k 2w resistor, does this have a big impact on sound? I have some kiwames in that size, but I'm worried about whether carbon film would be appropriate in this application.
Also just scored a pair of 2uf, 700vdc Solen Silver Sound agm series caps, going to try these after I get used to an all mundorf supreme sound.
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The small resistor 499r is what sets the current level so you want something reasonably precise, and preferably something with a low temperature drift. I usually use DALE RN55 or RN60 in that position. The larger resistor 150k isn't as important its really just limiting the current through the two LED's. I believe the ones supplied are Vishay PR series which is what i use myself, if you really want to gild the lily you could use the Vishay CPF series, but that's an unnecessary extravagance IMO. Both are metal film. I dont think changing either will have any impact in sound, unless you use something unsuitable for the job, which i belive would be carbon comps.
As far as i know Carbon Comps like the Kiwames are noisier than metal films when used in DC applications, power supplies etc. They also have much greater drifts with temperature so personally i wouldn't use them. Audio path / grid stoppers maybe, but not in a power supply.
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The small resistor 499r is what sets the current level so you want something reasonably precise, and preferably something with a low temperature drift. I usually use DALE RN55 or RN60 in that position. The larger resistor 150k isn't as important its really just limiting the current through the two LED's. I believe the ones supplied are Vishay PR series which is what i use myself, if you really want to gild the lily you could use the Vishay CPF series, but that's an unnecessary extravagance IMO. Both are metal film. I dont think changing either will have any impact in sound, unless you use something unsuitable for the job, which i belive would be carbon comps.
As far as i know Carbon Comps like the Kiwames are noisier than metal films when used in DC applications, power supplies etc. They also have much greater drifts with temperature so personally i wouldn't use them. Audio path / grid stoppers maybe, but not in a power supply.
Summed up the thoughts I had in my head. Thank you! The 500r vishays are quite precise as far as I'm aware, but next order I'll grab some Dales.
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Finally got around to retesting the LDR vs a few different conventional pots of 100k, 75k, 50k, and 20k and confirmed the large variation i was seeing before was down to the lower impedance of the LDR interacting with the tubes capacitance. Thanks Paul, i always learn something new from your posts :)
Back to the main issue, LDR vs regular 20k pot, i'm not seeing any appreciable difference in frequency responses or distortion using the equipment i have to hand, though i could convince myself it sounds more detailed to the ear. Pretty much decided not to use it, i'll stick to a vintage Goldpoint ladder attenuator for this build, but all this does have me curious about the 100k pot in the S.E.X. amp, would it benefit from a 75k or 50k unit instead....hmm
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Hey mcandmar,
You replaced the 680ohm ps resistors with triad chokes, did you also change the capacitance values of the caps used in the filter?
I was thinking of upgrading the 220uf electrolytics, maybe even increase it in capacitance to 470uf and then switch the 100uf lytics for 50uf ASC x386s blue line oil filled poly caps, and use 10uf asc blue line oil filled poly caps.
http://www.partsconnexion.com/capacitor_film_asc_blueline.html
Anyone have any thoughts, or has there been anyone whose done this in the past?
Specifically would love to hear thoughts from the Bottlehead guys.
PS my Elma switch is 50k. I think if the input impedance of your potentiometer is causing issues that has as much to do with the impedance of the pot as it does with the source.
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I stuck with the original values, but switched to Nichicon KX series just because.
I tried modelling the power supply circuit in PSUDII and for reasons i don't fully understand increasing the values of some of the caps actually made the ripple worse. Specifically the first two 220uf caps that form the voltage doubler, changing those values had odd side effects, and dramatically increases the current load of the transformer. It may be as much as quirk with the software more than anything else.
The ripple level at the following 100uf caps seems the most important to me as its directly supplying the output stage of the tube via a choke plate load, while and also feeding into the 8k / 22uf resistor down stream supplying the CCS plate load for the driver stage. Personally i wouldn't want to lower the value, and i don't think there is much to be gained if anything by playing about with the 22uf cap due to the CCS load.
My main source these days is the Bottlehead DAC, and according to the datasheet for the DAC chip it can happily drive loads down to 1k so i don't see that being an issue. Now that i am looking for it i went back and looked at all the various amps i know of using 6C45 tubes and almost all of them are using 20k pots. Now i know why :)
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I stuck with the original values, but switched to Nichicon KX series just because.
I tried modelling the power supply circuit in PSUDII and for reasons i don't fully understand increasing the values of some of the caps actually made the ripple worse. Specifically the first two 220uf caps that form the voltage doubler, changing those values had odd side effects, and dramatically increases the current load of the transformer. It may be as much as quirk with the software more than anything else.
The ripple level at the following 100uf caps seems the most important to me as its directly supplying the output stage of the tube via a choke plate load, while and also feeding into the 8k / 22uf resistor down stream supplying the CCS plate load for the driver stage. Personally i wouldn't want to lower the value, and i don't think there is much to be gained if anything by playing about with the 22uf cap due to the CCS load.
My main source these days is the Bottlehead DAC, and according to the datasheet for the DAC chip it can happily drive loads down to 1k so i don't see that being an issue. Now that i am looking for it i went back and looked at all the various amps i know of using 6C45 tubes and almost all of them are using 20k pots. Now i know why :)
Thanks for replying. Always good to learn something new.
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I wanted to thank you for your thread. I have stripped my SEX amp of the Stax module having moved it to another amp and wanted to set it up for speaker use. Your thread put me on track for the mods I was looking for.
Regards,
Aaron
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Part 4: Headphone jack resistors / Power supply chokes,
As suggest by Doc.B adding two 120ohm resistors in series with the headphone jack greatly reduced the background noise/hum on the amp making it almost silent. Refer to heater supply 100r resistors above.
Installing the two C3X chokes in place of the 680ohm resistors in the main power supply removed the remaining 10% of background hum. Having listened to the amp at length with various headphones i cannot hear a thing, just a lovely black background which makes a world of difference to the clarity/detail. Really happy with the result ;D
Specs for the C3X are 10Henries, 50mADC, 500ohms. They both measured ~470ohms on my meter however the power supply voltages measured before/after were all within three volts of each other.
As for physical placement, it would be possible to locate them to the side of the tube sockets on standoffs but i wanted to leave a bit of room around that area to replace the two capacitors in the future. The only other place i could find was the front edge of the chassis so they sit below the headphone socket and power switch. Obviously there are no issues with hum from their placement.
For the bracket i used a piece of steel strip i had, crudely bent to shape in a vice to fit around the various components and held in place by the volume pot. I lucked out as i had a washer under the volume pot to space the knob flush with the top plate that happened to be exactly the same thickness as the steel strip so it all just fell into place. Gave the bracket a quick sand/spray with clear coat to prevent rust and called it a day.
Which of the Hammond Choke is equivalent to the C3X?Thanks!
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https://www.hammfg.com/electronics/transformers/choke/153-159?referer=968 (https://www.hammfg.com/electronics/transformers/choke/153-159?referer=968)
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My eBay search spat these out recently which caught my interest, never seen any 6DN7 tubes with a metal base like that. Might have to source a pair for the collection ::)
https://www.ebay.co.uk/sch/m.html?_odkw=&_ssn=vivatubescom&hash=item23bd014ea5%3Ag%3AP34AAOSwLX5cT1H8&item=153494834853&_osacat=0&_from=R40&_trksid=m570.l1313&_nkw=6dn7&_sacat=0