Bottlehead Forum
Bottlehead Kits => Stereomour II => Topic started by: Jamier on October 31, 2016, 10:10:20 AM
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I'm building my second S II, this time with film caps in the PS. Since the films are so much larger than electrolytics, I had to build a taller base which took much longer than I had hoped.Then I built cradles for the caps which I suspended from the chassis using all-thread and nylon standoffs. As the amp nears completion I will need to connect the caps to the terminals with leads that will be about 4.5 inches long.So, my question is, should I twist the leads of each cap before connecting to the terminal or just run them directly to the terminal ( or does it matter)? I'll try to attach photos.
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Yes, I would recommend twisting the wires together. The objective is to minimize the loop area, so that local magnetic fields (from the power transformer mainly) do not induce hum currents. Twisting also reverses the direction of sensitivity with each turn, cancelling out much of the residual pickup.
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Thanks PJ,
Should I make the same number of turns per inch as the manual advises with the heater leads?
Jamie
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That's a reasonable goal, but not critical.
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I am almost ready to voltage test the amp. I have built it in the stock configuration and included all the required tests to be certain that it functions as intended before I begin the film cap substitutions. Is it safer to replace the caps one stage at a time,beginning with the last stage and working back? I feel like this approach will have greatest chance of success. I am concerned that if I change all the caps at once there could issues at the end of the PS that might be a problem, like increased B+ Voltage. Given that the film caps should have lower ESR, is this a possibility? If so I guess I will need to increase the values of the 130 ohm resistors that seperate the caps(?).
Jamie
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Some of you guys really blow my mind. Your Skills are just off the charts. That's just beautiful!!!!!!!!!!
Alan
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I've used Clarity Cap TC film caps in several projects from my Bottlehead Reduction to my VTA ST120 and they do a great job. I don't believe you need to change resistors. Another great feature is they discharge within a few minutes of turning off.
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Fancy mounting brackets, how did you make them?
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Hi Mark. This is the reason I haven't finished my F4. I'll be getting back to you for some more advice when I pick that up again. The cradles for the caps are made from 3/4 inch pine. I started by routing holes that are the same as the diameter of the caps. Then I cut those in half creating the cradles. Those half pieces are then placed back to back with about 1 inch of space between them and screwed down to a piece of 1/8 inch aluminum that has holes in it to allow zip ties to pass through it to hold the individual caps. Some end pieces of the same 3/4 inch pine completes the cradle.They hang from the chassis on All-Thread, washers and nuts. I sprayed them with rubber paint (Plastidip). It's all gotten from Home Depot (well, actually Lowes).MDF might work but the end pieces are screwed to cradles and screws just don't hold well in MDF.
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Nicely done, looking forward to seeing it finished :)
The F4 isn't as much fun to build, but its a wonderful pairing with a tube preamp. You get the best of both worlds without the compromises.
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Super effort I bet its going to sound just epic.
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Thanks to Alan, Rob, Mark and Jamie for the words of encouragement. I really hope this works out. If it does I will post all the construction details so anyone can duplicate and/or improve it.
Jamie
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And, to PJ, for the words of wisdom.
Jamie
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That is some great work. I wish I had good woodworking skills like that.
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I finished the stock build, resistance checked, voltage checked and now listening to the stock configuration. I will let this run for a 10-20 hrs to be sure there are no problems and then I will replace the last stage ( the last 100 uF caps) with Mundorf 100uF M tube caps. If that goes well I will change the second stage, listen for a while and then move on to the 220uF caps in the first stage. The second stage will also be the Mundorfs, the first stage will be replaced with Cornell-Dubilier 947C series 230uF / 1KV caps. I chose these particular capacitors for a few reasons. They meet the required specs, have good reputations and, while physically large, still fit under the new base that I built for the amp with enough clearance to remain well below the warmer components of the amp. I created adequate ventillation in the base (I hope) and suspended the new caps below this level feeling that air will enter above the caps to keep the rest of the components cool, carrying the heat out the top leaving the area around the new caps relatively cool. The replacement film caps also have screw terminals which made this process much easier with all the in and out that comes with fitting, etc. Originally the plan was to use ASC PP in oil but I could only find 50 uFs which required 8 of them. I tried several configurations but I just couldn't get them under this base with enough room to spare so I had to go with Mundorfs. So as this process moves forward I will compare each change to the stock SII that I built a few months ago and make progress reports.
Jamie
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I have about 15 hours on it. How long should the amp sit without power before I start clipping the electrolytic cap leads? The bleeders should work pretty fast, right?
Jamie
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I replaced the last stage PS caps with the Mundorfs (100uf). I got everything soldered and decided I should voltage check terminals 26,27,34 and 35. It's very tight in there when the capacitor cradles are in place. When I attempted to check 34 I must have touched 35 at the same time and.....
Well, you know what happened. The LEDs on the left channel of the C4s board are out. I am hoping that is all that is wrong. Any way I connected the amp to my system just to hear what the right channel sounds like. I only had it up for about 10 minutes before shutting it down but it seems like the amp has greater detail and a bit more bass. I'm considering taking the C4s board out of the other SII but I don't know if that is going to solve all of the problems. Does anyone have advice?
Jamie
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OK, up and running. When I shorted 34 and 35 I cooked the 130 ohm resistor preceeding the last capacitor stage on the left channel. I was lucky enough to get ahold of the Queen today. She sent me a few new resistors, so I decided to take a 130 out of the other SII to continue with the cap substitutions( THANKYOU Eileen !). I now have the last two stages replaced. I have a couple hours on it now. The difference between this and the stock amp is not subtle. The detail is improved and the bass is better. It just sounds more substantial. Last night I thought It might take me weeks to get back to this point. I'll give it quite a few hours in this configuration before changing the 220s in the first stage. If one were to swap only these last two stages it would be very much worth while. It really is the 220s that require the big base and all the work that comes with that.
Jamie
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I finished the last (actually the first) stage today. I have about 4 hours on it with the 220s replaced. The improvement with this change is all about noise, that's about it. It is really quiet now, almost black. There was not the dynamic improvement that came with the first two stages though. So, to sum it up, at this point I think you get about 60 percent of the improvement with the swap of the last stage caps.The swap of the second stage gets you about 30 percent of the improvement. The last stage gets you about 10 percent, but it's the stage that requires the taller base and a lot of work.So, if you want it all take the leap and get out your power tools. If you only want most of the improvement, just build some nice, sort of tall corners for the stock base and your almost there.
Jamie
PS: Pics Attached
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I should correct myself. Swapping the FIRST stage gets you about 10 percent of the improvement. Sorry for the ambiguous language.
Jamie
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I want to post a final comment on this topic:
I have had the SR circuit installed in the Film Cap version and in the Stock version of my two SII amps for several weeks. After much comparison ( before and after SR) I can honestly say that prior to the SR install, the Film Cap version seemed to have a better low end and more detail than the stock version. After the SR install the two amps sound nearly identical two me.Film Caps might have better bass but I can't swear to it as my A to B comparison requires break down and set up time, so it's not exactly instantaneous. So, I really don't recommend swapping out the PS caps, I don't really see any advantage, other than the film caps may last longer, but with the amount of work that it required, you could definitely change your electrolytics a lot faster.
I have considered the possibility that the lead length on those film caps is so long that perhaps it is offsetting the advantages of those big caps, so I might shorten those to see if there is improvement. But at this point, I really think that the circuit is so optimized that changing certain parts out for more expensive and less convenient versions yields very little improvement, especially since the SR circuit came along.
Jamie
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Jamie - Thanks for posting the results of your cap mods and comparison with the SR upgrade. Although it is now an old thread, your observations are helpful to people like me who are looking to play around with tweaking their build.
Regarding the lead length on those big caps: did you get around to shortening them, and if yes, did it change anything? If the concern is that there may be hum/noise induced by magnetic fields in the amp, you could try experimenting with copper tube shielding wired to ground. Copper refridgerant tubing comes in 1/8 and 1/4 in, is easily curved, and is inexpensive - I think around $10 for 4+ feet of the stuff. I will be experimenting with it in the coming weeks.
p.s. - incredible build! Nice routering!
cheers,
Derek
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Derek, I have not shortened those leads. If I were to do that I would eliminate the possibility of installing the DC filament upgrade. There would not be enough room for everything.After many hours of comparison between my dead stock SII and the film cap version there is very little difference between the two. I don't think those leads are picking up enough flux to be audible. Also, as I mentioned back then, I don't think the cap upgrade was a significant improvement. It was so much work, that in the beginning I wanted to believe the improvement was there. But, after hundreds of hours on both amps, I really believe that there is very little difference.So, my advice to anyone posting the results of mods and upgrades; is wait a while and be sure it is real. I definitely pulled the trigger too soon on the film cap upgrade result posting.If I were to describe the "very little difference"; the film cap version might have a slightly better bottom end, but it is not quieter. I think it's way too much work for what you get.
Jamie
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Thanks, Jamie. That's the gist I took from your original posts - but I wanted to check to see if anything had changed. I was contemplating going down the expensive cap upgrade path, but now I won't. My next step may be to put a BeePre in front of the SII. Other Bottleheaders have raved about the soundstage, clarity and dynamics of the BeePre.
cheers and thanks,
Derek
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Jamie - further to your point about jumping the gun on deciding whether a mod actually changes the SQ: my sense is that this may be a particularly difficult issue to pin down because it's hard to take into account the role played by the brain-ear and learning. I suspect it's possible for a mod to make a slight change in sound that pushes a music artifact above what I'll call an individual's "notice threshold" - such that a previously unnoticed detail becomes noticed. But thereafter the brain-ear knows the detail is there and can listen for it, potentially hearing it even with removal of the mod that first made it noticeable. I believe I experienced this yesterday when switching between unbalanced and balanced configurations. When I switched to balanced, improvements in detail were immediately obvious, but after switching back to unbalanced after an hour of listening, I found that the unbalanced sound had magically improved too! But some quick A/B testing on selected tracks confirmed (for me) that the difference was real - but now that I've "learned" the new detail, I can hear much of it even in unbalanced.
If there's anything to my foregoing speculations, this suggests a really inexpensive way of adding extra detail to one's listening: listen to one's favorite music on a better system (friend or audios store), find the hidden detail, and then go back and hear much of the same on your own system. :D
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The realization that came to me after that whole cap upgrade thing is; My acoustic memory is pretty shitty and I think that's probably true for most people. I did not have a rapid A/B comparison setup. That is absolutely crucial for making comparisons on these modifications/upgrades.
Jamie