Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: dumbo on June 02, 2010, 04:32:44 PM
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First kit, first post, already feeling greedy. Wondering what success others have had upgrading the Crack. I have the Speedball on order. Silver wire?, stepped attenuator?, etc. I understand these items may eclipse the price of the kit, just curious if anyone has tried.
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A stepped attenuator isn't a bad idea. You can also upgrade the 160uf caps at the output (voltage rating needs to be 150 or greater).
Better wire and RCA jacks are other decent options. I would go with continuous cast copper wire over silver, and maybe switch to cardas RCA jacks if you're comfortable drilling out the chassis holes a little.
Fortunately, the Crack performs well enough for these upgrades to be sensible.
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Just based on the decription and without having built it for the Crack, I would say install the BH Speedball upgrade kit above all else.
Next in terms of how much the sound of your Crack might change would be different tubes. You have lots of choice.
I am personally very much into "quiet" amps and I will try to reduce anything resembling hum and noise ... always.
I have changed out the RCA jacks, but mostly because I wanted more robust ones, not so much because I expect better sound.
I will probably cut more holes into the top plate in order to increase air flow. Any decrease in temperature inside the chassis will slow the ageing of parts and will keep your Crack sounding great longer.
Finally, how about better headphones?
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Finally, how about better headphones?
[/quote]
Got a pair of HD800s. Not sure I will be upgrading those anytime soon. How about the headphone jack? Anyone have a good replacement?
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Got my kit today and looking forward to building it. My plan for upgrading is to build the kit as is, without any modifications. The 'upgrades' I have in mind include;
- Speedball
- Replace the headphone jack with a high quality locking Neutrik type
- Replace all resistors with Tantalums or non-inductive film types
- Replace all capacitors with film types, even on the PSU
- Replace sockets with teflon
- Replace volume control with DACT or Goldpt
- Replace IEC inlet with one that has both filter and fuse
- Replace RCA with a Neutrik XLR
- Replace cabling with solid silver or solid copper
Actually, that is pretty much everything! The joys of DIY!!! Looking forward to first listening!
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The threads in the Crack folder have a lot of improvements. My favorite is an improved signal path cap at the output. That is the capacitor you listen through. Bottlehead has selected the best capacitor they can afford to put in the kit at the price point they sell it for but it can be made better.
The stepped attenuator will also be in the signal path. PJ has appropriately pointed out that any amplifying device only modulates the power supply, therefore the power supply is in the signal path. Bottlehead is very careful about selecting the power supply for specific properties. Check here before modifying the power supply, but do that for sure.
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Got my kit today and looking forward to building it. My plan for upgrading is to build the kit as is, without any modifications. The 'upgrades' I have in mind include;
This should have the greatest impact, along with tube rolling. I'm liking a 5998 right now.
- Replace the headphone jack with a high quality locking Neutrik type
I'd suggest modifying the headphone plug to a Neitrik rigtht angle plug if you are going to bother with this.
- Replace all resistors with Tantalums or non-inductive film types
Careful here, you need to know what design parameters determined the composition of each of the original resistor. Resistors in the power supply must have an adequate voltage and power rating, resistors on the PC boards must in some cases be very precise metal film resistors, in other cases once again power and voltage ratings are critical. Grid stoppers may be best if left as carbon composition. Really other than that there aren't that many resistors in the circuit once speedball is in place.
- Replace all capacitors with film types, even on the PSU
You will need to add "make much bigger chassis to hold them. Much bigger." I do however think this might be somewhat audible.
- Replace sockets with teflon
This is probably fine. I had heard years ago of Teflon sockets that were getting loose due to cold flow, but I haven't heard that recently.
- Replace volume control with DACT or Goldpt
IME the Goldpoint with Dale resistors sounds best. It might be interesting to try transformer volume controls. Figure on calling up the architect for another addition on that chassis plan.Sometimes it's easier to add another story than to add a room. A very tall box might hold all this extra stuff.
- Replace IEC inlet with one that has both filter and fuse
Those little Corcom style things are only for frequencies that are higher than we really need to worry about. Probably better off with a bigger outboard power conditioner that filters down to something like 50kHz. Or you might find just as good a result from putting one of those little Panasonic CMCs and a couple of AC rated caps around 10uF or so at the transformer primary. By now it may just make sense to call a commercial contractor to build your chassis...
- Replace RCA with a Neutrik XLR
Yeah, if you have converted to XLRs in your system this is a good idea.
- Replace cabling with solid silver or solid copper
The wire is all solid copper as-is.
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Actually, that is pretty much everything! The joys of DIY!!! Looking forward to first listening!
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What are some good stepped attenuators that are reasonably priced and where could I find them. I also wanted to buy a metal knob for the volume control and wanted to know what the shaft dimensions were.
Thanks,
Tom
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Replace all capacitors with film types, even on the PSU
You will need to add "make much bigger chassis to hold them. Much bigger." I do however think this might be somewhat audible.
You're not kidding.
The two 100uF and three 220uF Solens I have coming are 2.2" by 2.8" and 2.4" by 4.5" respectively. I may need a second chassis for these puppies (or a taller base).
Looks like the DACT CT2 attenuator will fit with the Speedball mods though.
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tdogzthmn,
I am not sure what you consider "reasonably priced" but here are two stepped attentuators (the websites list the dimensions) for around $150-$175:
Goldpoint (you can order from the website):
http://www.goldpt.com/compare.html (http://www.goldpt.com/compare.html)
DACT CT2 (you can order from DIYCable.com http://www.diycable.com/main/product_info.php?cPath=31_71&products_id=274 (http://www.diycable.com/main/product_info.php?cPath=31_71&products_id=274) ):
http://www.dact.com/html/attenuators.html (http://www.dact.com/html/attenuators.html)
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I was thinking under $45. I saw some goldpoints listed on ebay but for those prices I would much rather buy the speedball.
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I have used stepped attenuators from two auction site sellers located in the Far East: vintage_audio_lab and gigawork. They always have some items listed on the site and more in their stores.
Their prices are definitely reasonable and the units that I received worked just fine.
What are some good stepped attenuators that are reasonably priced and where could I find them. I also wanted to buy a metal knob for the volume control and wanted to know what the shaft dimensions were.
Thanks,
Tom
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In the power supply, fitting three 220uf film caps will be tough. Instead, run the stock first and second caps with the resistor between them, then use a Triad C7X and a 47-100uf cap after. This will impart 90 percent of the benefits of big film caps without the crazy space requirements. The C7X should knock the noise down enough to get away with this.
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Awesome responses. Exactly what I was hoping for. Thank you very much. I plan to build the kit stock at first except for upgrading to silver wire (don't want to wire it twice) and then upgrade each part one at a time. Should be a fun learning experience.
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The Schurter 1A power entry module with line filter has approximately 30dB of attenuation at 50khHz for common modulation [and nearly 0dB for differential]. That's not bad. In addition to that it keeps all the RF crap out that might cause trouble.
The reason why I don't always use them is that they are really best at keeping noise from inside the device away from the line [the Crack isn't causing any as far as I can tell], plus there is a potential for ground loops when these filters live in more than one device, plus Doc's proposal to use some X2 caps etc is more flexible and effective.
Schurter filter graph attached, solid line is common, dotted is differential:
- Replace IEC inlet with one that has both filter and fuse
Those little Corcom style things are only for frequencies that are higher than we really need to worry about. Probably better off with a bigger outboard power conditioner that filters down to something like 50kHz. Or you might find just as good a result from putting one of those little Panasonic CMCs and a couple of AC rated caps around 10uF or so at the transformer primary. By now it may just make sense to call a commercial contractor to build your chassis...
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Three resistors and one capacitor will add about $1000 to your Crack on the street. Just kidding, we're not in the drug business here.
You can run this in PSUD II ahead of time to make sure that I am not pulling your leg.
Keep the three 220uf caps, keep the two 270 Ohm resistors in the B+ power supply, add a Panasonic TSED 470uf 250V cap as your fourth cap [one cap], parallel the two existing 270 Ohm 5W resistors with a 360 Ohm 2W resistor each [the combined value for the parallel resistors is something like 154.3 Ohm - this adds 2 resistors], and finally connect the new capacitor that you are adding with a new 150 Ohm 5W resistor [this is the third resistor].
I just finished that change and I'm blown away. Total expense way less than $10.
I measured THD+N before and after. The graphs are too large to attach. Shrinking has to wait until tomorrow. It's late. Try it anyway, this is the biggest gain I've had from any modification in 30+ years of building gear.
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Actually I have read, but not heard, that the Acoustic Dimension 41 step attenuator is king... But in the days of $1000+ headphones, a 41 step ladder attenuator for 200 Euro is not shocking... I was actually thinking of building a parallel crack, new chassis, etc, but keeping the power transformer. The original, and the upgraded, and compare the differences.
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Grufty,
Thanks for the work on the PSU tweaks -- just may do that myself.
Here's another stepped attenuator from Poland:
http://www.khozmo.com/
They are 48 steps, priced about the same as goldpoints and shipping is free. I hear they are rather large, but I can't access anything with the dimensional information.
If these would fit in the Crack and/or Stereomour, I may pick one up.
-- Jim
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A pic of the Goldpoint Mini-V compared to stock. The chassis plate hole will need to be enlarged and the 1.1" knob just barely covers the small hole to the right of the pot hole. Should have gone with the next size larger knob.
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Three resistors and one capacitor will add about $1000 to your Crack on the street. Just kidding, we're not in the drug business here.
You can run this in PSUD II ahead of time to make sure that I am not pulling your leg.
Keep the three 220uf caps, keep the two 270 Ohm resistors in the B+ power supply, add a Panasonic TSED 470uf 250V cap as your fourth cap [one cap], parallel the two existing 270 Ohm 5W resistors with a 360 Ohm 2W resistor each [the combined value for the parallel resistors is something like 154.3 Ohm - this adds 2 resistors], and finally connect the new capacitor that you are adding with a new 150 Ohm 5W resistor [this is the third resistor].
I just finished that change and I'm blown away. Total expense way less than $10.
I measured THD+N before and after. The graphs are too large to attach. Shrinking has to wait until tomorrow. It's late. Try it anyway, this is the biggest gain I've had from any modification in 30+ years of building gear.
For what it's worth, the installation of the Speedball upgrade may make this mod less noticeable, as it greatly improves PSRR. Not to say that the Crack isn't quiet in stock form too.
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I ran a few quick and dirty measurement of my very nearly stock Crack build to have a baseline before any changes/upgrades. The graphs that I am attaching here are THD+N measurements at 1V rms at the output of the Crack. In each graph the blue line is the measurement of the Crack channel under test and the red line is a self-measurement of the test device to make sure that everything is in order.
This one here is the measurement with the stock PSU. I'll post only the measurements of the left channel. The right channel measures almost exactly the same.
Please let me know, if you would prefer not to have any measurements posted here. These look pretty nice, so I figured: why not?
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This one is after the PSU modification that I described in an earlier post.
All PSU frequencies and their harmonics are way down, 120Hz is more than 20dB lower. THD is also slightly lower, not that it matters much. Most of it is very benign 2nd harmonic which the ECC82 family leans towards.
Now I'm really looking forward to the Speedball upgrade, especially after reading Doc's comment that it greatly improves PSRR.
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Posting measurements is fine as long as the reference voltages etc. are included as you did, and posting comparative measurements like this a great idea. Thanks for doing so. It will be interesting to see what you get with the Speedball.
I might suggest trying different 12AU7s too, as that might influence the 120Hz level at the output.
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Man, I am impressed, posting measurements is great, especially when you are comparing mods! PM me your mailing address and I'll send you a choke to try in the power supply.
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Early impressions of the Speedball upgrade would tend to suggest to me that any big money upgrades should be done after you've installed it. That's kinda what I was figuring from Doc's impressions. Of course, there's nothing wrong with experimenting with the stock unit but I usually upgrade with some kind of sonic improvement in mind (I'm cheap and lazy so I try not to waste time or money).
Whew! I have to say that I love the way the upgrade makes vocals sound! I'm listening to "Raising Sand" (Robert Plant/Allison Krauss).
Outstanding!
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Steve,
If you haven't heard the HDTracks 24/96 version of "Raising Sand", you should try it. The CD is good, the high-res version is fanastic.
-- Jim
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That's the one I'm listening to Jim. Not too shabby for digital (especially Tattered Rose).
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Steve,
Yes, not bad at all. Looking forward to your impressions of the Crack with some other cans, and als what others will have to say about both versions of Crck.
-- Jim
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I got to do a comparison yesterday @ CanJam. Really, for the $99 + your time you can't go wrong with the upgrade. It should be the FIRST thing you upgrade IMO. Install Speedball!
The difference is very significant.
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I got to do a comparison yesterday @ CanJam. Really, for the $99 + your time you can't go wrong with the upgrade. It should be the FIRST thing you upgrade IMO. Install Speedball!
The difference is very significant.
What was the thing you noticed most between the two builds? I've been a little squeamish about adding a CCS to the Crack, as it seems like the results on my S.E.X. amp and Quickie have resulted in a quicker, but less warm and more pentode-like sound than the resistor (or choke) load.
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I suppose the result is similar, but I'm not sure it was necessarily less warm. I should have spent more time going back and forth, but once I went to the upgraded one I never went back and listened to the stock one! And I was back in there three or four times hooking my modded Nano up to it to steal another listen.
I think ironbut can help characterize it better as he has probably spent more time comparing the two.
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I am thinking of wiring my amp with cotton insulated copper wire. If the wire is unshielded will that cause problems and noise during use?
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The stock wire is not shielded, just insulated. If you do buy cotton covered wire, be sure to get solid core. I've seen a few builds go really badly because stranded wire was employed.
My preferred cloth covered solid core wire can be found here:
http://www.tubedepot.com/wire.html (http://www.tubedepot.com/wire.html)
Just be sure to pay attention carefully, as stranded and solid wire types are listed side by side. I especially like this wire because the cotton is bonded to the PVC underneath, so you can strip this as though it is normal PVC coated wire. Another nice aspect is that a little bit of overheating will make the PVC shrink away a bit, but the cotton will remain.
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I found the wire on hifi collective. Its solid core copper AWG 28, 6N cotton insulated. Its all white so I would have to label each strand during wiring so I dont loose track of the connections.
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That should work OK for everything but the heater connections, where it will be pretty thin to get the job done IMO.
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Wow! Speedball!
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Yes, WOW Speedball.
I used to feel that my Enhanced Sex/Hammer Dynamics speaker setup was a more involving listening experience, but now with the speedball upgrade the Crack /DT770(600 ohm) combo comes much closer to being in the "listening room".
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Thanks guys! The cathode follower setup on the 6080 is a really neat way to get the output impedance down to where it can run a pretty broad range of high impedance headphones, but the CF is kind of an imperfect beast in terms of distortion with an ordinary resistive load. Remembering the dramatic improvements we heard when we added a C4S load to the CF in the Foreplay preamp oh, so many years ago made it a certainty that I would try one on the 6080 in a Crack just about as soon as the solder was cool on the prototype. PB found a nice beefy transistor for the job in the form of the TIP50, and the project was a go. Gotta admit in this case the end result exceeded my expectations, and I've been using the C4S circuit for something like 15 years.
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nsorens were those huge caps part of the kit or an upgrade you installed? Thanks.
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Those are definitely non-stock.... They are the AXON True Cap 100uF / 250VDC caps that JREBMAN found at PartsConnexion, thanks JREBMAN!
I built Crack stock at first and listened to the electrolytics that came with the kit. The stock parts are very good and the AXON's only make a subtle improvement.
The Speedball upgrade is NOT subtle, it is huge improvement as everyone is reporting.
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Here's another one upside down.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fimg13.imageshack.us%2Fimg13%2F83%2Fdsc2932crop640.jpg&hash=79fcdca4f4b5bf33c87742e1348ce4d46b150c3a)
Most of the "extras" make up a regulated 12.6V DC heater supply for the driver tube. Mind you, the reason is not that I disliked the 6.3V AC heater supply. It works great. I just wanted more constant working conditions for the cathode follower independent of my choice of driver tube and its heater current draw [and vice versa].
You can also see the additional B+ supply capacitor and resistor. At this point everything still fits inside the chassis, sort of.
I haven't measured anything yet. I'm enjoying the music way too much.
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I couldn't resist.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fimg532.imageshack.us%2Fimg532%2F7758%2Fcrackleftat1v1khzoutwit.jpg&hash=10a82d9b7c33db876d4924420dbfd260872377a4)
This is again at 1V rms out - Crack with Speedball upgrade left channel blue - control red.
S/N improved to better than -70dB. THD improved to just above 0.1%. 2nd still dominant, 3rd at roughly -90dB, all higher harmonics buried in the noise, power supply completely inaudible.
That's only part of the story really, because the music just sounds incredibly "right".
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Here's another one upside down.
Most of the "extras" make up a regulated 12.6V DC heater supply for the driver tube. Mind you, the reason is not that I disliked the 6.3V AC heater supply. It works great. I just wanted more constant working conditions for the cathode follower independent of my choice of driver tube and its heater current draw [and vice versa].
You do realize that there is some headroom for heater current in the PT3? You could probably draw up to another .5 to 1 amp on that winding without huge issues...
I'm glad to see that the PEC pot fits nicely!
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Nice PEC pot, where did you find it? Been looking for another one of those for this amp but they are getting harder to find...
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Digikey has them. I just checked.
This one came out of my box of goodies.
Nice PEC pot, where did you find it? Been looking for another one of those for this amp but they are getting harder to find...
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Thanks, I don't know why I didn't think of trying Digikey! Got one coming now...
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I couldn't resist.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fimg532.imageshack.us%2Fimg532%2F7758%2Fcrackleftat1v1khzoutwit.jpg&hash=10a82d9b7c33db876d4924420dbfd260872377a4)
This is again at 1V rms out - Crack with Speedball upgrade left channel blue - control red.
S/N improved to better than -70dB. THD improved to just above 0.1%. 2nd still dominant, 3rd at roughly -90dB, all higher harmonics buried in the noise, power supply completely inaudible.
That's only part of the story really, because the music just sounds incredibly "right".
I would have been curious to see a graph of the baseline Quickie before any mods. How much do you think the noisefloor and THD dropped once using CCS's as plate loads?
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Look at reply #20 in this thread.
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Grufty,
Can you comment on the speedball vs your PSU tweaks? I know you got some nice results with the extra RC stage and resistor value changes, but how did that compare to the speedball?
I ask because I know that once a couple of friends hear my Crack, they're going to want one for themselves but they probably won't want to spend too much on upgrades.
Thanks,
Jim
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Woo-hoo, just found a dual 100k pec pot in my "junk" box. Definitely will put this in the Crack and save the expensive TKD for the stereomour. Man, my junk box hs been very good to me with this project -- 4 black gate NH 150 uF 350v (two matched to within 2%), the matched pair of 2.7k caddocks, and now the PEC pot, oh, and a pair of Vampire gold over copper RCAs.
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Look at reply #20 in this thread.
Ha! I knew I thought there was such a graph posted already.....
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I didn't have a lot of time with just the PSU change, but I was very happy with the improvement considering the minimal effort and the minimal price.
I paralleled the kit resistors, because it was quicker and easier, but if you build with this change in mind right from the start, then you can just go with three 150 Ohm resistors and the extra cap. The B+ voltage will be about 10 V higher than stock, but that doesn't seem to hurt.
When I first turned on the Crack after the PSU change I had to check twice if it was on at all. It was so quiet.
The combination of better signal to noise ratio and very nice final cap in the PSU also work a lot of magic on the music presentation. I felt much more engaged, drawn in, happy to be listening.
For less than $10 ... any day.
Grufty,
Can you comment on the speedball vs your PSU tweaks? I know you got some nice results with the extra RC stage and resistor value changes, but how did that compare to the speedball?
I ask because I know that once a couple of friends hear my Crack, they're going to want one for themselves but they probably won't want to spend too much on upgrades.
Thanks,
Jim
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I have finally entered the land of diminishing returns along the Crack upgrade path.
The latest status is mostly due to tube rolling. I found a very nice E80CC tube and a used 5998 that was both cheap and probably never used. The only other change from my previous post is that I biased the 12.6V DC heater current.
The output voltage is still 1V rms. The measurement setup is unchanged. This time I'll post both channels - the left channel has always behaved marginally better than the right channel, but the difference is really academic. The only harmonic distortion that matters at this point is just a hint of 2nd. There is no noise to speak of considering that this is a tube circuit.
Left:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fimg143.imageshack.us%2Fimg143%2F7686%2Fcrack5998pq1vleft.jpg&hash=fa196067667406068ef28abcd1c465c31987da7d)
Right:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fimg641.imageshack.us%2Fimg641%2F3475%2Fcrack5998pq1vright.jpg&hash=9150f780870c1e468fb042d38bb9d87322b63afa)
I am not really good at describing how these "upgrades" translate into a better listening experience. The end result to me is possibly best described as: great intensity combined with a deep sense of calm, however contradictory that may sound.
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Grufti,
It only matters that you like what you have done.
I would have thought that the graphs would show some increasing noise floor as you got below 100 Hz. Some tilt, but it is essentially flat. There is also no tilt in the high frequencies, no tube rush. It certainly indicates you have a very clean build.
I see no hum sneaking in the right channel. The "misbehaving" left channel shows a repeating 60 Hz component. And that makes no sense. The right and left channel are the same power supply. For the most part they should have the same noise. Maybe there an AC lead to the left channel that is a little too close to the audio signal wire?
Nice graphs! I like it!
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At this extremely low level most of the channel differences are likely to originate in the E80CC tube itself. Some of the original data sheets have a cautionary remark telling you that one of the tube sections will have better noise and THD performance. The E80CC tube that I'm currently using actually stands out for best measured performance from the "other" side.
I certainly like what I'm hearing. You might want to go back and follow the progression from the first to the last posted measurements. There is quite a difference.
And mind you, all of my other "upgrades" so far have cost about as much as the Speedball. So I'm still below $400 total right now [$199 Crack, $99 Speedball, less than $100 everything else ... no fancy $1,000 power cords], with the help of the introductory pricing for the Basic Crack kit and the minimal outlay for a few parts under the hood and two different tubes on top.
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A pic of the Goldpoint Mini-V compared to stock. The chassis plate hole will need to be enlarged and the 1.1" knob just barely covers the small hole to the right of the pot hole. Should have gone with the next size larger knob.
Does the stock knob fit?
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Now that I got one I can answer my own post. No, the goldpt post is to long. which is to bad...I like the stock knob with the finishes I went with...:-(
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use a Dremel or some sort of grinder to shorten the shaft. Make sure to cover the entry of the shaft, and any other areas where metal debris might enter the wiper mechanism with tape. You can make the shaft to fit the knob you want to use.
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Yes, I am considering using my drumel...a scary proposition considering the cost. Guess you just go real slooow. I was wondering why they would make it so long, then I saw that they sell knobs!
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In the power supply, fitting three 220uf film caps will be tough. Instead, run the stock first and second caps with the resistor between them, then use a Triad C7X and a 10-20uf cap after. This will impart 90 percent of the benefits of big film caps without the crazy space requirements. The C7X should knock the noise down enough to get away with this.
I think I want to try this. I've got a nice asc 20uf motor run cap that would work. I've always wanted to try them in the signal path. I'll just have to pick up the choke.
For the first mod $15 bucks is cheaper tham film caps for the output or the speedball. Of course both of those things will eventually end up in the circuit anyway...
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I'm relatively new to the DIY stuff (I assembeled a PCB-based portable amp) so some of the lingo is pretty foreign to me. "Getter", "heater", and "cathode/anode" to name three. I've since done a little reading and now know what those things are, but when I read here about installing different potentiometers, do all stereo ones have the same connection points? Will a TKD, or ALPS, or PEC be soldered in the same as the stock one? Same for the headphone jack? From what I've seen, it seems Neutrik is easily the most popular but is it the only choice as an upgrade? Hope to get a "it's shipped" e-mail soon so I can get my hands on it and visualize some of these things.
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While you are waiting for the kit to arrive you should read this thread:
http://www.bottlehead.com/smf/index.php/topic,173.0.html
The first item is the meter you must have to verify your kit is put together properly. It can be used to verify how a pot is wired. The fact is that Alps often have 4 lugs per channel. The placement of the input, ground and wiper lugs is not a standard thing so to be sure you should measure the pot to make the determination.
The same thing for different headphone jacks. But they most often come with instructions that indicate the right, left and common leads. Shoot, you will want to familiarize yourself with the meter anyway before starting on the kit.
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Thanks Grainger. I already have a nice Craftsman meter and have used it on other projects (interconnects, power cables, etc) so that isn't an issue and I've read the thread you linked me to. I have all the "necessary" tools, and many of the "nice to have tools" so I think I'm covered there (I hope so anyway).
I read about octal sockets, the various voltages for tubes, and different capacitors and it seems many folks here have a good deal of knowledge about electronics, or at least tubes, and how everything works together. I am ashamed to say I don't even know how to read a schematic. I know some of the symbols but that's about it. Hopefully over the summer when I'm not in school I can get that taken care of.
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Somewhere I posted how to figure out how a pot should be wired. I should save it in a file and cut and paste it when the subject comes up.
BTW, the Alps pots I am familiar with have a fourth lug, per channel, for adjusting the loudness compensation. It isn't used for our applications here.
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I used a PEC pot as my pot upgrade and it wired in exactly the same as the stock one. I just needed to enlarge the hole a bit; oh and the shaft is a bit longer too so the knob does not set all the way dow.
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I can heartily recommend these miniature stepped attenuators sold on Ebay:
http://cgi.ebay.co.uk/DACT-Type-21-Stepped-Attenuator-Potentiometer-100K-2A3-/120474000457?pt=LH_DefaultDomain_0&hash=item1c0ccf5c49
I've tried PEC & Alps pots, plus more expensive chunkier stepped attenuators, and now use these for every project. I can't hear any colouration and the signal path will be shorter than many larger attenuators (including ladder type).
No brainer!
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I saw those and they look to be pretty decent for the price. I think one of the biggest things with stepped attenuators is the quality of the mechanical switch that they use and that makes sense. But the same can be said for the quality of the cheaper potentiometers. Then there is the fact that 21 or 24 steps is often said to not be enough, and depending on the source and the way the pots were built in terms of taper, especially not enough near the lowest end of the range (low volume/gets too loud too soon). Ive been obsessing over the volume pot thing since I first decided to build the amp. I was considering one of those pots or possible the Valab 24 step (series) attenuator. But I have a feeling I would had to use resistors on signal inputs to tame the volume at the lowest settings. I have a cheap wirewound alps in another amp and it tracks surprisingly well at the low end of the volume range and throughout and sounds fine but being a small board based amp, doesnt leave much room for mods for comparison.
I've prewired an Alps Blue Velvet pot for the Crack and may use it or I still may go ahead and use the stock alpha pot in the initial build and swap the Blue Velvet in later to see for myself if I really hear a difference.
I can obsess on end about little things and drive myself crazy eventhough I full well realize that I wont really know how anything behaves until it's up and running. I probably didnt inspire much confidence in Tubeglow. But I can offer this. You arent alone, Tubeglow. Well, I can generally follow the schematic but dont know what everything means/does. But I do know, that after looking over the instructions, this is an easy build as long as you can solder. Ive asked plenty of basic (some dumb) questions on this board in preperation for building the amp, and everyone has been helpful and friendly. Im sure some were gritting their teeth with some of my questions but all patient and helpful nonetheless. This is a safe place :-)
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Laudanum,
Have you read this page from Bottlehead VoltSecond?
http://www.siteswithstyle.com/VoltSecond/12_posistion_shunt/12_Position_Pure_Shunt.html
He gives you a number of ways to set your volume range. About 1/2 of the way down the page, look at figure 2.2.1, there are several options for trimming attenuators. The one with a switch allows for having very small steps then at the flip of the switch you get full range.
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I have used the stepped attenuators from gigworks in several projects and am quite happy with them; I have a B1 and a little buffer/amp I built for my car. Somehow though the PEC carbon pot seemed more a appropriate choice for the crack. Just my 0.02!
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Laudanum,
Have you read this page from Bottlehead VoltSecond?
http://www.siteswithstyle.com/VoltSecond/12_posistion_shunt/12_Position_Pure_Shunt.html
He gives you a number of ways to set your volume range. About 1/2 of the way down the page, look at figure 2.2.1, there are several options for trimming attenuators. The one with a switch allows for having very small steps then at the flip of the switch you get full range.
Ive seen the page but didnt get that far down. Not sure I want to get that "fancy" with but I may down the road if needed. Thanks for the switch info, didnt even know it was there.
To keep it simple, again, if needed (I dont even know yet) I was looking at the Goldpoint site and the resistor values for L-pad attenuation that Paul helped me with. I have the resistors if needed. I figure, if it gets too loud right off the floor then I'd probably have more than enough max volume that I could afford some fixed attenuation. But, I havent built it yet. Painted the tranny bell end black. Just finished the cabinet this afternoon, poly is drying. I was going to paint the chassis plate black but I decided to leave it as is with the brushed aluminum. I think I like the contrast better with the black jacks, knob and tranny. I needed to make a 3.5mm to RCA input cable and did that this afternoon. Think Im going to make a shortish 1/4" male to 3.5mm female output cable (two pairs of headphones have 3.5mm plugs so I would need to use the adapters anyway). Just been doing the prep stuff that I needed to do to get it all out of the way.
Thanks
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Up from the depths....
I've been getting interested in upgrading the volume pot, got some good leads here.
I'm wondering if we shouldn't start a new thread dedicated to upgrade potentiometers/attenuators?
I'm trying to figure out that balance between something really good without going overboard that also is as close as possible to "drop-in" without serious mods....
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In my experience, both the goldpoint and the PEC pots fit easily with just a bit of filing to open the mounting hole a tiny bit. They both clear the inside of the box and other components too.
HTH,
Jim
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Cool, thanks for the info.
Now, seeing the PEC for maybe $30 vs the Goldpoint (Mini-V?) for $150+ begs the question: Is the Goldpoint *really* that much better?
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I haven't done any a/b comparisons, but I do believe the goldpoint is more transparent, but that said, the PEC is quite decent (I have one in my SE el84 amp), but I personally don't like stepped attenuators on headphone amps -- just not fine volume control. Yes, it's the mini-v I was talking about.
-- Jim
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I can see how a stepped atten could be annoying, I'm gonna go for a PEC.....
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I installed a Goldpoint 'Mini-V' in my Crack, but only because I had it around from a project I wasn't satisfied with and tore down for parts. I don't think I would have spent the $140 just for this amp. It does sound great, much better than the Alps blue I originally installed. I don't have any experience with the PEC so I can't compare the Goldpoint with it.
Shawn P.
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I installed a Alps blue velvet in mine this past weekend(along with an output cap(s) upgrade). Loving the results so far.
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Alps Blue Velvet is similar in price to the PEC. I wonder who would win in a shootout? I ordered the PEC already, just wondering if I shouldn't have waited for more info.
Can you explain the output caps upgrade you did? What did you use? Did it require much shoe-horning or any serious modification?
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Actually, the Alps Blue velvet pots can be had for a little less than 1/2 the price of the PEC from what I have seen. About 12 - 14 dollars at Mouser. Twice that through audio parts suppliers. I think they are great value for the money ... especially in terms of tracking at low volume but I think it sounds just fine. The PEC is supposed to be a nice pot and only in the 30 dollar range so not super expensive. I'll probably give one a try after a while just to see if I can hear a difference. If I had to pay $25 or so for the ALPS, I probably would have spend the extra 10 bucks on the PEC.
Outputs caps fit will depend on what caps you decide on. Something smaller, relatively speaking, like the Solen, Axon, Erse, Mundorf MKP etc. is actually a pretty easy fit. I went with the Mundorf MKP's. They sound nice in Crack, I think. I dont detect the "glare" that the Solens can sometimes impart. It's an upgrade from the stock electrolytics that isnt difficult to detect but the stock caps dont sound bad at all. The film caps are a bit smoother sounding and a bit more detailed and treble seems just a bit more extended as well. I know that one Bottlehead reported a little lighter bass from whatever film cap they used (may have been solen or axon). I havent noticed any less bass with the Mundorfs. I think it was definitely a worthwhile upgrade, eventhough the Mundorf mkps arent considered high end or boutique caps.
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Just another opinion about output caps for the Crack: they do make a difference, but not as big of one as some may think. Tube rolling and the Speedball upgrade definitely changed the character of the amp; the 100uF Solens I put in there simply gave a bit of refinement. (I detect no glare in this particular application, FWIW). The stock electrolytics are surprisingly good, with solid bass and crisp (if somewhat "zingy") highs. The film caps sound smoother and less edgy in the treble, without losing detail. Bass seems to be about the same. I normally feel that output caps contribute a lot to an amp's sound, but the upgrade is surprisingly subtle in comparison to the plate loads and swapping out the 6AS7 for a 5998 (which IMO was the single biggest contributor to a change in sound quality). The only difficulty with the huge film caps is how to mount them securely. The small stock capacitors are much easier to deal with in that regard!
I also changed out the pot, and that made a small difference in clarity, in addition to better tracking/balance between channels. I used a cheapo stepped attenuator from Hong Kong, and it's holding up great so far.
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The Alps seems to have perfect tracking all the way down. The stock pot didn't sound bad at all, but it didn't track as good as the Alps. With the stock pot the right side would kick in before the left. Not really a big deal as I never listen to levels that low and it didn't seem to affect the upper volume at all.
I would still like to try one of the Chinese attenuators from e-bay. I tell you though the little pins on the Alps are a PITA to see and solder.
The caps I installed are the AXON 91
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I agree with Dr. Toobz, the speedball is by far the most effective upgrade. I settled on the 5998 as well, along with a Mullard CV4003. The 5998 provided some gain as well as giving the bass more control, less thump and more clarity. I replaced the output and the last cap in the PSU with Mundorf MKPs, as well as bypassing the other PSU caps with 2.2 uf MKPs. I think the biggest bang for the buck upgrade for me was the filter choke in the PSU, about $14 from Mouser, but it takes some creativity to fit it on the plate.
Shawn P.
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I already have Speedball and ran a 5998 for about a year until I hosed it on accident. Now I run a 7236, a 'computer' version of the 5998, which sounds exactly the same if not a tiny tiny bit better. Tele smooth plate on the front end....So, upgrading the vol pot to a PEC and may as well do the caps if it's not too much trouble anyway, knowing it will only be a subtle improvement....not much else to upgrade without serious modification...I'm still trying to figure out what to do there though.
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I agree 100% that Speedball provides a more signifigant change in sound than the Film output caps and also agree about the potential changes/improvement being greater with tube rolling.
I installed the film caps BEFORE I did the Speedball upgrade. Just guessing that this could have impacted my perception of their impact, but by strict definition, I cant exactly call the change "subtle" in that I didnt have to listen intensely to recognize the change in sound. But again, I am in total agreement that it isnt as signifigant as the other upgrades/changes mentioned. "Smoother" is probably the best single description of the film caps affect. As I mentioned previously, I think the stock caps sound good and in retrospect, I could happily enjoy Crack with them, and did so for a while. But the film caps are a worthwhile addition to the upgrade path IMHO. Just not on the top of the food chain so to speak, when prioritizing.
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Now I run a 7236, a 'computer' version of the 5998, which sounds exactly the same if not a tiny tiny bit better.
The 7236 is actually a computer rated 5998A, which is a slightly different tube to the 5998. It looks like it uses the flat plates of the 6080/6AS7 rather than the dimpled plates of the 5998, but still has the higher gain and slightly lower heater current of the 5998.
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Back to the more recent upgrade questions, I'd put in a vote for the TKD 2CP2511 or 2508 pots. They track and sound better than an Alps, even to my tin ears. And I've personally avoided PEC pots because of numerous reports that they can be noisy and scratchy, particularly at low volumes.
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Thank you for the clarification on the 7236. I highly recommend it as a cheaper alternative (though not a sexy ST shaped) to a 5998.
The TKD pot fits in there ok?
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Thank you for the clarification on the 7236. I highly recommend it as a cheaper alternative (though not a sexy ST shaped) to a 5998.
The TKD pot fits in there ok?
I used a TKD and except for having to enlarge the hole it fits fine. I can't compare it to any other potentiometer because I installed it during the original build but I can't hear any issues with it at all and it's very smooth.
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I installed a Goldpoint 'Mini-V' in my Crack, but only because I had it around from a project I wasn't satisfied with and tore down for parts. I don't think I would have spent the $140 just for this amp. It does sound great, much better than the Alps blue I originally installed. I don't have any experience with the PEC so I can't compare the Goldpoint with it.
Shawn P.
Hi Shawn,
Are you using the speedball upgrade? It doesn't look like there would be enough room between the Mini-V and the C4S board.
Tom
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TKD pot and Mundorf MKP's output caps installed by a tech friend of mine, I only just got the amp back at lunchtime....won't have time to listen until later tonight.
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Um...YES. A definite improvement. As other's have said, not night vs. day but noticeable. Nicey nice.
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Um...YES. A definite improvement. As other's have said, not night vs. day but noticeable. Nicey nice.
I dont know about the pot but I like the Caps. Not bad at all for affordable "basic" MKP's.
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Reviving an old thread again, but this has some solid info in it and hoping to keep all of it in a relevant place.
I am planning on putting in the Belton tube sockets, and since this means some major rework, I plan on replacing some parts as I go along. I was just going to order resistors, but read the following and would just like to double-check before I order incorrect parts.
I am quoting DocB from the first page of this thread: "Careful here, you need to know what design parameters determined the composition of each of the original resistor. Resistors in the power supply must have an adequate voltage and power rating, resistors on the PC boards must in some cases be very precise metal film resistors, in other cases once again power and voltage ratings are critical. Grid stoppers may be best if left as carbon composition. Really other than that there aren't that many resistors in the circuit once speedball is in place."
I do not have Speedball installed, but will be replacing the metal film resistors and probably the power supply resistors. Resistance will stay the same, I plan on slightly increasing the wattage, but am not sure about the "voltage and power ratings" mentioned in the above quote. Would a 500V rating be sufficient? I also know that an increased wattage leads to a bigger resistor and potential mounting issues. Anything else I need to be aware of?
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The 270 Ohm resistors need to have long leads so that you can mount the one between the two 6 lug terminal strips on the power transformer. Most 270 Ohm 5W resistors won't work here, so you'll probably need one 10W and one 5W part here. These are not particularly audible in my experience.
I can't see any reason to change the 270K 1W resistor, but if you need a new one, any 270K 1W resistor will work fine.
The 22.1K resistors are chosen for good quality and adequate power dissipation. You could spend a lot of money on nicer resistors, but they won't deliver the performance that the Speedball does. (Same goes for the 3K cathode resistors)
-PB
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Hi PB,
Thanks for the response. These changes are purely cosmetic in nature and I feel that I can do a better job now than I initially did. Plus, I really like working on the Crack. It is a really simple, yet elegant design that makes it very easy to experiment.
I will be replacing all the metal-film resistors with the mustard coloured Vishay / Dale ones on Mouser. Not very expensive and purely cosmetic.
Regarding the 270 ohm resistor, I was thinking of either using the Stereomour trick of using insulation from another wire to cover the exposed wire, or just make fly leads and solder the resistor to that. Again, purely a cosmetic change.
For the 270K resistor, still undecided. In any case, for both of the last 2, I will look up their specs and find something that can handle the 500V minimum.
Once all of these changes are implemented, I will have the base Crack built exactly like I want it, and can probably add Speedball at that point.
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I will be replacing all the metal-film resistors with the mustard coloured Vishay / Dale ones on Mouser. Not very expensive and purely cosmetic.
The two 22.1K resistors should carry at least a 1 Watt rating.
Regarding the 270 ohm resistor, I was thinking of either using the Stereomour trick of using insulation from another wire to cover the exposed wire, or just make fly leads and solder the resistor to that. Again, purely a cosmetic change.
A 10W part will actually look better back there.
For the 270K resistor, still undecided. In any case, for both of the last 2, I will look up their specs and find something that can handle the 500V minimum.
Any old 270K 1W part should work, the 500V rating isn't necessary.
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How is the sound quality changed if all the crack's stock cable changed with pure silver core cable? I'm a newbie in diy, very interest when hear the silver core cable interconect sound character. But a little fatigue in high tone, its get sibilance and 'overload' in treble. So is it possible to get the best sound when apply all the stock cable with it?
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I just noticed that my bottlehead crack has reversed left-right channels (i bought it already built some time ago) - I would like to fix this and also upgrade the volume pot if i'm anyway taking it to an electrician.. any suggestions for a good value pot?
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The Valab 100K ladder type attenuator has been used by a number of people here. It's only $33 on eBay.