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In Reply to: I'd like to address 3) power supply....... posted by drlowmu on March 2, 2007 at 23:00:06:
The whole idea of a reservoir cap is to act as the termination of the PS, as far as the amp is concerned. It is supposed to be like a "wall" between the amp and the power source. If the reservoir cap is sufficiently large and of good enough quality, then everything that comes before it in the PS (the 'boiler room', so to speak) will be inaudible. That includes the power tranny, rectifiers, smoothing cap(s) and choke(s). Their job is simple, namely, to supply a nice clean, smooth, reliable B+ of the required voltage to the reservoir cap.In the straightforward case of supplying power for class A amps, current demand doesn't change significantly and any small variations in demand are easily absorbed by the reservoir cap. DCR in the 'boiler room' of the PS is really not an issue, capacitor input filters work fine, everything is nice and simple! The only challenge is ripple, but judicious application of sufficient inductance and capacitance in the right places can reduce that to the point where it becomes inaudible. And if that doesn't work, shunt regulation can save you (don't knock it, it works).
On the other hand, the more complex problem of supplying power to class AB amps, where the current demand varies with signal level, is more of a challenge. This is where low DCR and choke input filters suddenly become important, to minimize voltage sag. Again, regulation can be a great help, but I digress!
My key point is that a power supply has no business sounding like anything. If you find that components before the reservoir cap are affecting the sound of a class A amp in any way, it's because your reservoir cap isn't doing its job properly, and that is where you should concentrate your efforts to improve the PS. It really is as simple as that.
Follow Ups:
Ray,Its YOUR whole idea of a power supply and what you say is really outdated, misleading to this poor poster, and very wrong. Class A amps and single ended amps need just as good a supply as AB amps, if not better!! Particularly single ended amps where the supply is embedded in the audio circuit.
Of course, I will bet you 1,000,000 dollars you have never even TRIED the type of supply I have proposed, so you are speaking from inexperience with both types.
Have you not learned anything from my over two years of posting about this complex subject??
YES, I am aware of what you profess, but I am also aware, after personally building BOTH types of supplies, with 80% of my builds Class A1 BTW, that you have got it wrong. You have it wrong on ALL counts, including the need for low ripple on the 45 output stage of course. Thats pretty funny. I couldn't have paid you to write a better post on what NOT to do. One good trait, you are consistent.
Have you built such a supply for a Type 45 that I descibed? 'Bet not!
L1/C1/L2/C2 are $10.79 for each L and under $13 for each C !! The only real cost is a decent power trannie, but one may relax that part's criteria some, as its the Ls that must be driven, not the Power Trannie !! One must think in dynamic terms with supplies, not in static terms as you did above...its all wrong Ray, sorry. Been there done that, and it truly sucketh.
Just read my 245 post's listening description...'think I fabricated it - and profess it publically ?? I'm not that stupid. Ask Messers John Swenson, C.Y, Nickel Core, and Dr. Y. Chung....they too are delighted . Why remain living in the dark ages??
Tell you, and ANY potential detractors what, ........... just build and listen to the supply I previously described re: the 245 amp's report. Use very heavy gauge ground and B+ wiring, and we will put an END to ANY of this bickering and wasting of bandwidth up here.
***** Its easier to build it and listen to it, than to post outdated "theoretical" supply dogma - that doesn't sound good. ******
Keep an open mind, heart and ear. Enjoy !!
Sincerely, Jeff Medwin
And certainly not intended to mislead anyone. Just my own point of view, based on what I have learned from a number of recognized sources on the subject, my own experience and plain common sense as I see it. Is it really wasteful of bandwidth to post my own honest opinion, just because it happens to differ from yours? Don't forget, this is a public forum.
Ray,The brickbat theory only applies when the capcitance is supplying current the PSU cannot deliver. If the cap does this, it discharges, and the timeconstant of recovery is based on the transformer. The transformer will be in circuit during this time, and so will be audible.
Thanks to the transient nature of a music signal, this happens an awful lot more than the theory suggests, unless your PSU is huge. Thats one of the key reasons why many DIYers upgrade the PSU, and things typically sound better....
Just my experience of the situation.
Never heard it called that before :) I do favor a fairly big reservoir cap, up to several hundred uF if it seems appropriate. I know this goes against some other people's PS design philosophies, but I'm unaware of any real downside.Certainly, if the reservoir cap gets drained despite having high capacitance, possibly by frequently repeated heavy transients in the music, then it has to be quickly replenished. That's where low DCR in the tranny, rectifiers and choke(s) obviously scores. However, I do not see the point of low C and low H.
Ummm, a SE amp is going to have the PS seeing a *VERY* variable signal. Cut the final off, and demand from the PS goes to zero. Swing the grid full positive and demand doubles.I think you were talking about Class A PP amps. Even those see a rather interesting AC component.
Sure, SE doesn't balance like PP and the demand on the PS will be modulated by the signal. However, the reservoir cap absorbs this modulation, if it's doing its job as a decoupling cap, rendering the net DC demand essentially constant. We rely on decoupling caps at every stage, including the final.
The big final reservoir cap absorbs the modulation all right, and it also absorbs the MUSIC SIGNAL in a SE amp ....thats why we now design with all Cs under 50 uF, and maybe even under 40 uF.'Same absorption applies to high value ( over 1/2 HY ) and high DCR ( over 10 ohms ) chokes ( loses the music ) .... and absorption of the music signal through the SE supply also occurs with inadequate gauge wiring ( loses the music ).
Your thinking ( and posting ) is only static Ray, its outdated / incorrect now in relationship to optimized SE audio amplification, it needs to become dynamic.
"The big final reservoir cap absorbs the modulation all right, and it also absorbs the MUSIC SIGNAL". To my understanding, the modulations ARE the music signal. They're meant to be absorbed, otherwise you have inadequate decoupling. Where the "hot" end of the OPT primary goes to B+ it should be the same as ground, so far as the signal is concerned. If it isn't, we have a problem.I'm not sure what you mean by "low C". Fifty or more years ago, 16uF caps were commonly found doing service as reservoir caps. Now, that's what I call outdated! Fortunately for us, it's now much easier than it was then to make big caps with high working voltages, so we are free to make our choice based on our needs, like the 40uF-50uF caps to which you refer.
'Same absorption applies to high value ( over 1/2 HY ) and high DCR ( over 10 ohms ) chokes ( loses the music )' I don't know where you get this from. As I explained, a good reservoir cap stops the signal dead. Whatever comes between the wall socket and the reservoir cap (be it the usual power tranny, rectifiers, smoothing cap(s) and choke(s) or a bank of car batteries) should make no difference to the signal.
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