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In Reply to: RE: PAS-3 filament voltage doubler capacitance posted by sbalfour@att.net on October 10, 2013 at 17:48:48
It’s hard to know. There are a lot of reports on-line, as you have noticed, but not a lot of direct correlation with sonic results. If memory serves, Frank Van Alstine at one time used something like 40,000 here. More recently I exchanged e-mail with him where he quoted something more like 10,000. Who knows why he might have dropped it, if that is indeed what happened.I rebuilt my PAS using something like 24,000 total – and it doesn't sound right. I am wondering if it is too much. There could be other issues. Waiting for time to investigate further.
Edits: 10/11/13Follow Ups:
Peter,
After a certain amount of UF there is a point of diminishing returns. Once something is quiet, it is quiet. You can't get anything more quiet than quiet.
I am skeptical about the other responder saying that he hears differences when he goes or clips in more UF and then unclips them. But it's his ears and who am I or anyone else to judge what he hears. I wish I had hearing that good.
To me(getting off subject a bit), I hear more of a difference(for the better in my opinion) when I took an ST-70 or a pair of MK III's and took the choke out and put in another filtering section, than I ever would putting in huge amounts of UF on a filament supply. That choke deadens the sound immensely. Most will argue that it is needed or a choke of some nature that can handle the current. I am not into an argument. All I can say is what I hear.
I feel like this is an insufficiently explored topic in forums, at least in the forums I frequent. Either in DIY projects or in factory-assembled big name high end products, it does seem like upgrades or higher end models increase the microfarads. I do not think it is an issue of reducing the ripple to infinitesimally lower and lower levels. There are probably other reasons, perhaps less “sag” or something else that may not be widely understood or discussed. I have considered that increasing the energy storage might obviate the need for regulation.The question seems to be the threshold: how much is too much? I am not even really concerned about a question of diminishing returns. What I am most interested in is at what point larger amounts of capacitance can actually adversely affect the operation of the amplifier and/or the sound (of course, what constitutes an adverse effect on the sound to one person may not be the same to another).
For instance, Stereophile magazine reviewed the Octave Audio RE 290 amplifier that sells for $10,000 - $13,500 depending on whether you purchase the “Super Black Box,” which is a module that increases the capacitance in the power supply. The reviewer described his perception of the differences in sound with and without the Super Black box, which improved the sound in most ways but not in all ways, subjectively. I don’t recall if the review specified the amount of capacitance in question, but I am including the link.
Then there are the $5,600 each Decware Zen Tori monoblocs that sport 4,400uF for the B+ (not sure if that’s 4,400uF per monobloc or combined between the two).
Well, these amps presumably had designers who knew how to design a power supply with this much capacitance. However, adding huge amounts of capacitance to a Stereo 70 or PAS might be a different matter. We know that the time constant could be an issue as well as other performance parameters that could be adversely affected. I do not know how to calculate this stuff, but I can say that increasing the capacitance in my Stereo 70 from the original 90uF to 500uF sounds great - but at what point might it actually cause problems if I wanted to increase it more?
100,000uF for the PAS filaments? You've got me on that one. I’ve never tried it, and, no disrespect intended, but I have my doubts about it. But, I guess I will have to defer to someone else who has actually tried it.
With regard to the choke, it is there to reduce ripple in the B+. It's an inductor in series with the power supply, and I have wondered if it would also affect the high frequency response of the amp for the same reason it reduces the ripple? Certainly worth experimenting with.
Edits: 10/18/13 10/18/13 10/18/13 10/19/13 10/19/13
Hi Paul,
You have every right to be skeptical. I don't blame you at all. I've always felt the same way about you removing the ckokes. Not because you don't hear and like the improvement in sound. Only because it goes against conventional wisdom. That doesn't mean it's wrong though, only that you like it better, and I've always wondered if I would too.
One thing I will take exception to (unless I'm making an incorrect assumption here) is when you say,
"To me(getting off subject a bit), I hear more of a difference(for the better in my opinion) when I took an ST-70 or a pair of MK III's and took the choke out and put in another filtering section, than I ever would putting in huge amounts of UF on a filament supply."
Have you tried actually temporally clip leading in the extra capacitance into a stock ( meaning unregulated) PAS supply and listening to it that way? Maybe I misread your post, but when you say, "than I ever would" it sounds like contempt prior to investigation. I've always wanted to try your method of removing the choke from my ST-70, and listening for myself. Unfortunately, my work schedule allows me enough time to listen to music, but not enough to solder as often as I'd like. That's one of the things I admire about you, you get a lot of projects done.
Back to the subject at hand. Temporary adding extra caps to the PAS filament supply (via clip leads) will only take you a couple of minutes. I'd like to hear about your results. I'm not suggesting this will give you more improvement than removing the choke, let me be clear about that, because I simply don't know. Only that caps are cheap, the original poster had them in his "junk box", and adding extra capacitance is easy.
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