Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: JamieMcC on April 04, 2014, 01:43:03 AM
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I am considering whether to do the 12au7 choke mod on my crack and replace the last electrolytic capacitor with a film one.
Looking around at what 12au7 chokes are on offer I noticed there is quiet a difference in specs and prices.
Is there generally a favoured type re materials & performance specs brand etc that I should look out for when considering. I am guessing all chokes are not created equal even though they may look similar and marketed as the same?
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Are you going to put a choke in the power supply or as the plate load for the 12AU7?
If in the power supply the Triad C7-X is often used.
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Thanks that was handy I entered the Triad C7-X in the search box and found a useful thread on the topic. I belive the mod is replacing the resistor on the last cap in the power supply with the choke this would enable the Electrolytic cap 220uf to be replace with film cap uf? from my reading I picked up 4x 50uf F&T film caps the other day for not much money and thought I might try them in this configuration. I use sen HD650 and Beyer T1 so 300ohm & 600ohm impedance thought about trying them configured as 100uf-150uf-200uf it would be relatively easy and a bit of a exercise in how the sound is effected with differing values.
http://bottlehead.com/smf/index.php/topic,3498.msg30912.html#msg30912
Edit I'm thinking paralleling them up to achieve the different uf values will be fine?
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It is my understanding that if you replace the final cap with a film you need not use the same value, uF. So a 100uF or 150uF film will be a good replacement for a 220uF electrolytic.
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Jamie, you could have hours of fun playing with this http://www.duncanamps.com/psud2/ (http://www.duncanamps.com/psud2/) comparing the resistor to choke, different cap values, and see what effect each one has. I learnt a lot from it when building the supply for my AC quickie as some of the results were not at all obvious. Sometimes adding more capacitance actually made things worse, and using the simulator i was able to work out optimum ranges of capacitance and resistance for each position for a given load. Its a bit of a black art and i dont pretend to understand the math or theory behind the half of it, but it helped me cobble together a very quite and effective power supply with the exact voltage i needed at the output.
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Mark thanks for the link I will have a play with that later and see if I can make any sense out of it.
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Just had quick play with it, i dont have the exact details for everything but i'm estimating ~1.5mv ripple with the three 220uf caps as stock, with a C-7X choke i kept lowering the capacitance until i got back to ~1.4mv ripple and was using 220uf, 100uf, and 22uf so certainly getting into the ballpark where film caps are feasible. Of course ripple is only one part of it, there are many other factors to consider but as far as i know film caps will be better in those areas too. You have me thinking about the final 22uf caps in the S.E.X. supply now :)
I can post the two PSD files i made if the BH guys have no complaints, i assume there is an unwritten rule about not posting schematics or manuals bits on the internet?
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I have a Triad C7X in my 7N7 Crack. It made a very noticeable improvement in the reduction of background noise, better low level detail and timbre. The final PS caps are the same aluminium foil with waxed paper caps as the output. I run 60uF output (200 ohm & 600 ohm phones) and 30uF, (actually 32.2 with K5 bypass!), for final PS. The finals value was a trade off, better cap versus more capacitance. Real estate made the final decision for me.
Cheers,
Geary
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Geary, thanks for your input, am I missing anything in my assumptions that once the relevant resistor is removed the choke leads are soldered in to the same position as the resistor so effectively just a substitution all be it one that takes up more space?
Jamie
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Geary, thanks for your input, am I missing anything in my assumptions that once the relevant resistor is removed the choke leads are soldered in to the same position as the resistor so effectively just a substitution all be it one that takes up more space?
Jamie
Not missing a thing.... 270 ohm for 270 ohm and much more space!
Cheers,
Geary
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...The finals value was a trade off, better cap versus more capacitance. Real estate made the final decision for me.
Cheers,
Geary
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FLqyI9pG.jpg%3F1&hash=50d14853ed6fd890581466b9a349d6c9f8a62ac9)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FvTQTH1Q.jpg%3F1&hash=fd71624c092c659c987e45be9e15379be52ef8f7)
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Super thanks this is the one I am looking at
http://www.ebay.co.uk/itm/Triad-C7X-10H-90mA-smoothing-choke-/171093411086?pt=UK_Sound_Vision_Valves_Vacuum_Tubes&hash=item27d5f6450e
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.ebayimg.com%2Ft%2FTriad-C7X-10H-90mA-smoothing-choke-%2F00%2Fs%2FMTIwMFgxNjAw%2Fz%2F2pUAAOxyYSJR-35Y%2F%24%28KGrHqF%2C%21ncFH105MFgoBR-35%280ykw%7E%7E60_58.JPG&hash=deb03ac2ddaec521cd287f98c82ced52af041404)
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Geary, thanks love the picture and see you have been quiet creative in installing them, nicely done by the way quiet impressive actually.
Do you like how they working out any particular strengths? I also noticed you have not gone down the speedball route any particular reasoning behind that?
Its just interesting to hear about different approaches
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Mouser:
http://ie.mouser.com/ProductDetail/Triad-Magnetics/C-7X/?qs=%2fha2pyFadugK4YD5AhNIYyYhVBDO80YGMTl0YqP7zJk%3d (http://ie.mouser.com/ProductDetail/Triad-Magnetics/C-7X/?qs=%2fha2pyFadugK4YD5AhNIYyYhVBDO80YGMTl0YqP7zJk%3d)
Cheers,
Geary
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Do you like how they working out any particular strengths? I also noticed you have not gone down the speedball route any particular reasoning behind that?
They are strong in imaging and timbre. I am a PIO guy. I tried some MPP & MPP in oil, but just not to my taste. Speedball is awaiting BH shipping. I ran my AU7 Crack for quite awhile before doing the Speedball. The Speedball is an improvement, but there is, to me, a trade off, better detail for less warmth.
Thanks for the kind words!
Cheers,
Geary
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Love the double decker layout, very creative.
Jamie here is the idea fully implemented, i have no idea whos crack this is, its one of the many images i have saved from the gallery section before it got wiped out.
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Geary,
Your Crack is stuffed. And I don't mean that in an Australian way.
I like your adaptation to mounting all the bulky upgrades too.
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Mark thanks the pics posted really helped and saved me from making a newbie error. I had not been following correctly and had just wrongly assumed without looking at the schematic that the 270k ohm resistor which was removed was the regular shaped 1W one and not the 270 ohm 5W cement one which is sort of hidden from view.
Looking at the schematic the second 5W 270 cement resistor is before the last 220 cap and the 270ohm 1W is after so that make is starting to make sense. If I am indeed following the schematic correctly? Just want to be absolutely sure as the Crack is my first diy build and have no prior experience in electronics and what I have generally consider to be a black art!
Edit ah ha something be must starting to sink in that 270ohm 1W looks like it might be for draining the caps down as its after everything else?
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Looking at the schematic the second 5W 270 cement resistor is before the last 220 cap...
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2F5rennYq.jpg&hash=971afbc2f0fa7d155aedea17382c506dfe6f1487)
Cheers,
Geary
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The 1w is a 270K, thats just a bleeder across the + and - to discharge the caps on power down. The choke replaces one of the 270ohm 5w resistors. I would have thought the first one which is over the transformer however now that i look at those pics it looks like it is installed in the second position. I would want a bit of clarification from the BH guys on that one in case it was put there for a reason, perhaps the current or heat dissipation would be too much for the choke in that position.
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Mark, Geary, thanks, very helpful and much appreciate your holding my hand. Think I am on the same page now.
I had edited my above post re the bleeder as I actually had an inkling that's what it was for after pondering over the schematic some more.
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Just ordered the Triad choke it seemed rude not to after all your help guys :D
Cheers
Jamie
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With a Hammond 193C, you might be OK with just a CRC filter.
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Thanks Paul with the Crack is there any particular reason as two why the second resistor is normally replaced by the choke and not the first one?
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Hmm, I think I remember looking at simulations of replacing either resistor and concluding that it didn't make a whole lot of difference.
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There are two schools of thought:
On the one hand, the choke can pick up magnetic-field hum, typically from the nearby power transformer. So the choke should replace the FIRST resistor, allowing the later RC stage to attenuate any hum that gets into the choke.
On the other hand, the choke provides a higher impedance than a resistor, so if the last (third) capacitor is a high-audio-quality cap then you want it to isolate it as much as possible from the earlier, crappier capacitors in the power supply. So the choke should replace the LAST resistor, and be located and oriented to minimize pickup from any nearby magnetic component.
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Thanks wonderful info I feel like I'm getting a bit of education.
Does a choke get hot and need air to circulate round it to cool?
If I mount as in the pic below perhaps I can incorporate some form of shielding from the transformer with the materials used for the offset mounting some metal or composite channel section to create a base and partial sides or cover in copper foil shielding tape.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fbottlehead.com%2Fsmf%2Findex.php%3Faction%3Ddlattach%3Btopic%3D6030.0%3Battach%3D5460%3Bimage&hash=fe9edddb95e10e0d44d3b6c79ddbb26a69214f56)
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If you figure that the choke dissipates roughly the same heat as the 270 Ohm 5 Watt resistor, consider how much larger the choke is! Consequently, it will get warm, but not particularly hot.
I wouldn't shield the transformer or choke unless there is evidence that it is necessary. For example, if you laid your choke down so that it was oriented identically to the power transformer, you might need to expend that effort.
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I tried multiple positions with the 10H chokes i installed into my S.E.X. amp and didn't detect any interference issues. The two 150H chokes in the quickie were a different story though, they could detect a mains lead the other side of the room!
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Ok noted.
My Choke arrived earlier today which I thought was very quick unfortunately they sent me the a Triad C3X 10H 50mA by mistake the good news when I contacted the shop they said they would put a Triad C7X in the post straight away and I could keep the C3X!
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Are there any problem if I put two chokes instead of the two 270ohm 5w resistors on the top of the chassis like the SEX ?
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It's more of a space issue - you may find it difficult to fit them up there.
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If you opt for dual chokes don't mount them side by side. If they must be close mount them at 90 degrees to each other. But if you put them on opposite sides of the amp that should suffice for isolation.
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OK thanks.
another question: What are differences between the Triad C7-X and the Hammond 193C ? Is there a better one ?
As I plan to put the two choke on the top of the chassis, the Hammond will look better...
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The C7-X is a direct replacement for one of the resistors, where as the 193C would need a bit of a circuit tweak to work, though the 193C is the equivalent of two C7X's in terms of inductance.
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...
another question: What are differences between the Triad C7-X and the Hammond 193C ? Is there a better one ? ...
Well they are both chokes LOL ... The 193 weighs more than three times as much, has twice the inductance and a similar current rating, has 2/3 the DC resistance, it's enclosed instead of open frame, and it's mounted vertically. Costs a lot more, too.
Incidentally, I believe the current-production C7-X is in fact made by Hammond, to the original Triad specs (more or less). The original was chosen back in the days of the original S.E.X. amp (we are fast approaching the 20th anniversary of that seminal product!) because it was available from Allied at significantly less cost than other chokes of similar specs. It's been a go-to workhorse for Bottlehead in several applications, mostly because it works and we know its foibles.
Fortunately, a power supply choke is not usually a critical component. For Crack, you want a current rating of 70mA or more, and probably a DC resistance of 200-350 ohms to keep the power supply voltage pretty close to original. I don't think either PB (the designer) or I have actually modeled a choke power supply for this application, so no comment on the best inductance. There have been discussions on how to model power supplies, and what behavior is best, at the Tube-DIY Asylum. But go there with your cynicism intact and post wiht your flame suit on - there is a LOT of misinformation surrounding the good stuff, and people get pretty excitable on the subject.
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Thanks Paul I think I'll opt for the Triad C7-X and search for some transformer covers
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Hi all, just wanted to say thanks to all those who helped hold my hand with the choke installation details and share a couple of pics of how its turned out. Keeping the fasteners out of sight behind the transformer worked well I intend to go back over the connection with some better insulation or shrink wrap to make the connections look a bit more tidy at a later date.
(https://www.head-fi.org/image/id/5980074/width/900/height/900/flags/LL)
(https://www.head-fi.org/image/id/5980075/width/900/height/900/flags/LL)
(https://www.head-fi.org/image/id/5980078/width/900/height/900/flags/LL)
(https://www.head-fi.org/image/id/5980079/width/900/height/900/flags/LL)
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Well, that cleared up all my questions. Thanks everyone.
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The C7-X is a direct replacement for one of the resistors, where as the 193C would need a bit of a circuit tweak to work, though the 193C is the equivalent of two C7X's in terms of inductance.
What kind of circuit tweak is needed for the 193c?
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Add a 100 Ohm 3W resistor as a series component in the power supply to drop the voltage that the 193C doesn't.
This is kind of a moot point though, finding a place to mount that choke will be the tough part.
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Add a 100 Ohm 3W resistor as a series component in the power supply to drop the voltage that the 193C doesn't.
This is kind of a moot point though, finding a place to mount that choke will be the tough part.
I'm working on making a different base plate and box, something along the line of 12" x 12". Couldn't I mount the choke up top if I go this route?
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Yes indeed.
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Yes indeed.
Just to clarify before I order, I want two right?
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Yes indeed.
Just to clarify before I order, I want two right?
I don't know, I could see situations where 1, 2, or 3 of these chokes could be used. The specifics are up to you.
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http://ca.mouser.com/ProductDetail/Triad-Magnetics/C-7X/?qs=%2fha2pyFaduhbeVQomtZQm6Wo19J3RkQe24jRzwLg5Ow%3d
I just wanted to point out that new Triad C7X are available from mouser for $CAN 13.79. That is about the 1/2 the price as seen posted on ebay earlier in this thread. Possibly cheaper shipping too. From a reputable seller like mouser its a better deal all around.
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Whats the difference between the new and old?
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http://ca.mouser.com/ProductDetail/Triad-Magnetics/C-7X/?qs=%2fha2pyFaduhbeVQomtZQm6Wo19J3RkQe24jRzwLg5Ow%3d
I just wanted to point out that new Triad C7X are available from mouser for $CAN 13.79. That is about the 1/2 the price as seen posted on ebay earlier in this thread. Possibly cheaper shipping too. From a reputable seller like mouser its a better deal all around.
Whats the difference between the new and old?
Not sure if its a new version myself they look to be the same the specsheet Mouser link is dated 2006.
The Ebay ones I expect are brought in baulk wholesale most probably from Mouser and then just marked up for retail.
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Ordered mine early Wednesday morning from Mouser with other goodies. Received it Thurdsay afternoon at my work. That's from TX to Ontario Canada. Amazing turnaround.
Stuffed it in my Crack (lol) last night and heard it briefly. I used a couple 1" standoffs and I almost accidentally drilled through my transformer, but its in! I had to turn it off right away because it was 1am and I would have been there all night. This morning there is yet again more prat coming out of the PS and I swear its digging deeper for detail. Its worth it.
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Hi all, just wanted to say thanks to all those who helped hold my hand with the choke installation details and share a couple of pics of how its turned out. Keeping the fasteners out of sight behind the transformer worked well I intend to go back over the connection with some better insulation or shrink wrap to make the connections look a bit more tidy at a later date.
While it's the chokes I'm mostly interested in, what are you doing with the circuit that allowed you to use such small output coupling caps? I thought going that small would raise the lower -3dB point to a problematic degree.
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While it's the chokes I'm mostly interested in, what are you doing with the circuit that allowed you to use such small output coupling caps? I thought going that small would raise the lower -3dB point to a problematic degree.
Those are 10uF caps in parallel with some other caps.
-PB
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Not sure how to answer that myself but there is a graph on the forum somewhere that showed how the Cracks 3dB point changes by interpolating different capacitor uf values with differing headphone impedances which was quiet interesting. Perhaps someone will remember where it was posted.
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Is this the chart?
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I just want to make sure that this is the right choke (C-7X) for the Crack before i ordered them.Thanks!
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Yes that is it.
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Thank You!
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Does the choke need to be mounted away from the chassis or can I use velcro to secure it right on it?
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I believe it is a good thing to ground the choke metal.
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Others have mounted the choke on standoffs under the top plate. A look through the Gallery folder or in the Crack folder will yield a number of pictures.
The choke needs to be a way from other inductors, like the transformer, to keep it from picking up hum.
Yes, it needs the frame, mounting screws, tied to the safety ground.
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Thanks guys. The standoff idea seems like a good method. Will run to home depot tomorrow to pick up a couple :D
James
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Are you going to put a choke in the power supply or as the plate load for the 12AU7?
If in the power supply the Triad C7-X is often used.
I am still a bit new to electronics and schematics and such, but am I correct in thinking that if the Speedball upgrade was installed, then the place where the plate load choke upgrade would normally go in the stock Crack is no longer correct since the Speedball replaces some of the plate load stuff? If I were to replace some resistors with choke while having the speedball installed which resistors would I be looking at replacing? Seems all the info covered so far is only about the power supply chokes part of that, nothing on the plate load choke idea.
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Sorry, I can't help you with plate load chokes.
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We don't recommend plate loading chokes for the 12AU7, and I don't believe this has been done in the Crack. The Speedball will offer better performance than a pair of plate loading chokes without taking up tons of space or picking up on radiated magnetic fields. Plate loading chokes would also severely raise the 12AU7 plate voltage without additional modifications.
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Concurring with PB here - a long time ago I made a 6BL7 preamp with switchable plate loads - four different inductances and a C4S. No question about it, more inductance was always better than less, and the C4S easily beat out the highest inductance.
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Hello Gang,
I am preparing to install the C-7X choke. Is there any sense in twisting the two wires together or it does not matter?
My choke as a black dot next to one wire. Is there one "IN" and one "OUT"? Must that be considered at the time of connexion?
Thanks.
Richard
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Yes there is some sense to twisting the wires (minimizing the current-loop area.
The choke works by reducing the current fluctuations of the power supply, but it does not of course completely eliminate them. The twisted wires reduce the magnetic hum field generated by the remaining fluctuations.
The most important twisting is the heater power wires, where the fluctuating current is very high - 2.5 amps for the 6080 heater.
The dot usually signifies the start of the winding, standard practice it to use that with the highest AC voltage, i.e. the input of a filter choke. In this application the difference will be very tiny, so don't stress.
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Just installed mine ;D
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi60.tinypic.com%2F103wduh.jpg&hash=123d87f270cb89c92a4e9c1f558a8ee88af30e04)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi60.tinypic.com%2F30ubp91.jpg&hash=b1f8fc831d7420a5b018c32a0e24dd87299afbc1)
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How are you liking it?
I fitted my choke and swapped out the last 220uf electrolytic capacitor with a film equivalent at the same time I liked the results and thought them easily noticeable. But very interested to hear your thoughts on the impact of the choke in combination with the stock electrolytic capacitors.
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Thanks PJ for the concise and clear explanation, as usual.
I will twist the wires and connect them according to standard practices even if, as you state, it probably does not really matter in this case.
Richard
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How are you liking it?
I fitted my choke and swapped out the last 220uf electrolytic capacitor with a film equivalent at the same time I liked the results and thought them easily noticeable. But very interested to hear your thoughts on the impact of the choke in combination with the stock electrolytic capacitors.
I'm not sure whether it's the choke or if I took a break off my headphones for a couple of days (I seem to notice details better when I don't use my headphones so often) but I think there is improved sound stage and clarity in the lows. My ears can be fooling me as it always does so I cannot know that for certain. As for the blacker background I can't really comment on that. I still need to buy a DAC for my desktop it seems because I can still hear a slight hum. I can only hear this hum when the Crack is connected to the PC but on my laptop it is dead silent. It does sound very nice so the choke may have improved the overall sound.
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Hammond 158M can it be use for the CRACK?Thanks!
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Yes.
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Yes.
I just want to make sure,Thanks!
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Before i go ahead and install the CHOKE i just want to confirm that this is to replace the 270R 5W under the two caps.Thanks!
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Either 270 Ohm resistor can be replaced by the choke.
-PB
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I went with a non-standard mounting location for my choke since I decided on a couple diminutive Panasonic film caps for the output. Allowed the choke to mount on one side (a bit further from the transformer) and the film caps to mount on the other side. Almost looks like it was meant to be that way. ;)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi67.tinypic.com%2F24d31bt.jpg&hash=bb3455a310e3e089f16a4696aa3033a7039554c2)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi66.tinypic.com%2F2rx75t2.jpg&hash=19d34ee8bc171ce35b6995935893021b96dd83be)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi67.tinypic.com%2F259cym9.jpg&hash=49e568209e43d9fe28599d9c5a4641b67df92ee0)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi67.tinypic.com%2Fww0zet.jpg&hash=ba4f744e8573eef97788f211d8e0eaa9d25ae2c7)
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Either 270 Ohm resistor can be replaced by the choke.
-PB
I actually like the choke it did make the background quieter,What do you think of replacing both 270R 5W resistors with a choke(The issue is where to put the second choke but it's ok i will try to find a place for it by moving stuff around)?Thanks You for your reply!
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Some have just made a deeper base to allow room for the second choke.
You could also look for a choke with ~550 Ohms of DCR and more than 10H and just use a CRC power supply. The Hammond 158L may be a good choice. I would parallel the two 220uF caps on the IEC side terminal strip together after the choke.
(Note that I haven't tried this, so YMMV)
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Some have just made a deeper base to allow room for the second choke.
You could also look for a choke with ~550 Ohms of DCR and more than 10H and just use a CRC power supply. The Hammond 158L may be a good choice. I would parallel the two 220uF caps on the IEC side terminal strip together after the choke.
(Note that I haven't tried this, so YMMV)
I maybe able to put the second Choke on the Pot side,I don't want to do a circuit changed just incase i need to do some trouble shooting in the future at least i know that what i did is changed components.Thanks again!
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Don't know if it's worth it. Didn't really hear much of a change with the second choke. Tested with and without.
Just left it in nevertheless.
(https://ep1.pinkbike.org/p5pb13669239/p5pb13669239.jpg)
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Thanks for the info,Another question do i need to ground the Choke chassis?Thanks!
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Yes, all the iron should be grounded to the chassis plate, for safety reasons. It's good practice to insulate the iron from the plate so it can be grounded to a single point, preferably near to where the power is grounded.
The reason is to minimize the leakage currents in the chassis plate, and keep them well away from the audio circuitry.This reduces a potential source of hum.
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Yes, all the iron should be grounded to the chassis plate, for safety reasons. It's good practice to insulate the iron from the plate so it can be grounded to a single point, preferably near to where the power is grounded.
The reason is to minimize the leakage currents in the chassis plate, and keep them well away from the audio circuitry.This reduces a potential source of hum.
THANK YOU!
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Wow, this thread is loaded with great information! Thank you Paul J. and Paul B. for being so open in the forums, providing to-the-point, no-nonsense, clear information and advice to all of us. I've become a fan of both of your scientific and kind responses, and this makes me even more proud to be an owner of the Crack. :)
Paul J., I posted a question to you in the Crack thread at Head-Fi, but it's more sensible to reach out to you here. You've said, "I would never use less power supply capacitance (last cap) than in the output cap, and I'd prefer at least twice that - if it were my amp." Currently, I'm using three 68uF Audyn Q4 caps (2 outputs, 1 last PS), could you please explain what the difference instead would be if I used two 47uF outputs and a 100uf PS cap? Which would fare better in terms of bass roll off, the three higher capacitance 68uF caps, or two 47uF outputs and the doubled 100uF PS cap? My cans are 600ohm AKG K240 Sextetts, and I do have the C-7X choke installed. Thanks so much and take care!
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I don't follow the HeadFi forum - PB is the headphone guy. Hopefully he will post based on his much greater experience. I'll just give the theoretical argument:
The issue is that the PSU cap and output cap are effectively in series in the current loop; if they are both 100uF then the effective output capacitance is 50uF. Not an issue with 600-ohm phones. At 160 ohms, there would be a bass rolloff at 20Hz - lower than that and you would likely hear a loss in the deep bass.
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Is there an equation to calculate this? So, right now my effective output capacitance is 34uF from my 68uF caps, with bass roll off at 8hz using my K240. What if I increased the PS cap to 100uF but use 47uF caps for outputs? How much will the effective capacitance decrease in this case? Or does it stay the same as the output when the PS cap doubles the output?
And in that case, if using a PS cap that triples the outputs' capacitance, does the effective capacitance double the outputs (220uF last PS cap + 47uF outputs = around 100uF effective capacitance)?
Thanks so much for your response and your time. Take care!
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Please correct if I have this wrong. Still trying to figure this stuff out.
The -3dB roll off frequency is calculated by 1/(2*pi*R*C).
In this case, R is the impedance of the headphones in ohms and C is the effective capacitance of the last PS cap and the output cap in farads (not micro farads).
The effective capacitance of capacitors in series is calculated by 1/(1/C1 + 1/C2 +…).
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Which K240 headphones do you have? They have come in several flavors with different impedances.
Another issue that's worth considering is that when you start shrinking the last PSU cap in the Crack, you will let more power supply noise through,which is very undesirable.
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Hi Paul B. :)
I have the K240 Sextetts, 600 ohms.
Also, in the PSU, along with the last 68uF film cap and C-7X choke, I'm using 470uF electrolytics for PS caps 1 and 2. I'm happy to say, the background is dead silent even with the volume maxed out.
I'm just trying to decide if I should raise the last PS cap to 100uF and use two 47uF output caps. Considering my choke, 470uF PS caps, 68uF last PS cap, 68uF output caps, and 600-ohm headphones -- bass doesn't roll off till 8hz -- is there any other reason to have a last PS cap that doubles the outputs besides the bass roll off? What would you do if it were your amp and using 600-ohm cans?
Thanks so much!
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I'd use the 470uF->choke->470uF in parallel with whatever film caps you have, then use 47uF or 68uF caps on the outputs. The extra R-C power supply node shouldn't be necessary with the rest of the changes.
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I'd use the 470uF->choke->470uF in parallel with whatever film caps you have, then use 47uF or 68uF caps on the outputs. The extra R-C power supply node shouldn't be necessary with the rest of the changes.
I'm sorry, please forgive my ignorance, but what do you mean "The extra R-C power supply node shouldn't be necessary with the rest of the changes."? What's an R-C power supply node? Is it the final PS cap?
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I'm sorry, please forgive my ignorance, but what do you mean "The extra R-C power supply node shouldn't be necessary with the rest of the changes."? What's an R-C power supply node? Is it the final PS cap?
The extra RC power supply node is the 270 Ohm resistor and whatever cap follows it. With the choke and the increased capacitance, the extra filtering shouldn't be necessary.
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The extra RC power supply node is the 270 Ohm resistor and whatever cap follows it. With the choke and the increased capacitance, the extra filtering shouldn't be necessary.
Thank you, Paul for helping me understand. :) But what about the relationship between the last PS cap and the outputs for the "effective capacitance"?
If I don't use a last PS cap, just the two 470uF caps and the choke, how will that affect my effective capacitance? Will the 68uF outputs indeed effectively be 68uF or much less than that? Thanks!
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As PJ mentioned, they are effectively in series. The larger the last PS cap is, the closer your coupling cap will be to giving its corner frequency as though it was the only cap that mattered. With 470uF as the last cap in your power supply, your 68uF cap will perform better in this regard than if the last cap in the power supply was 220uF.