Power Supply Resevoir Size

[danielwritesbac]

Here's an on topic, yet craptastic, mistake that I did to a power board.
All of the caps were 2200u but there were different models (oh no!!). Assuming that the first cap at the bridge rectifier really takes a beating, I put a high spec cap there, since it had better datasheet ratings, and then that was directly followed by ordinary caps to complete the rest of the capacitance. Yep, you guessed it--shouty amp with no bass. I replaced the high spec cap with Cornell Dublier's Mallory SEK, both durable and fairly awful for signal (you'd never want it for an output cap, but it worked great as a power cap). The results were beautiful and the bass reappeared. Unfortunately for me, replacing the deluxe (low esr cap) with something ordinary (mallory sek), wasn't my first guess. This took a while.
Question:
Could I have fixed that situation by putting a loss (cable or resistor or diode or longer trace) between different models of caps?

[Kindhornman]

Daniel,
Could you do me a favor. At this point I do not care about the name on the cap. List the actual specification differences that are making the changes you are talking about. Otherwise what it appears to be is you are trying every perturbation to try and use an expensive boutique cap somehow. Is that really the point here, or are we looking at specifications and damn the manufacturer of the components? If standard capacitors are giving you a superior result in your opinion why keep chasing this application. Numbers and actual differences will mean much more to me than calling out a brand name.

[tsiros]

Has anyone mentioned that the distortion of the amplifier due to power supply ripple, when the amp is driven hard, will be relatively insignificant to the distortion that will coming out of the speakers, which will be driven hard, since the amplifer is being driven hard?

[Nico Ras]

Originally Posted by tsiros

Has anyone mentioned that the distortion of the amplifier due to power supply ripple, when the amp is driven hard, will be relatively insignificant to the distortion that will coming out of the speakers, which will be driven hard, since the amplifer is being driven hard?

That was a very early observation in the thread Tsiros, that the sound character may be affected in a greater or lesser way. Re-read some of the comments around post #45 and your own post #50. I believe that power supply hash is entering via the overall NFB loop and because it is not present in the input signal, thus the difference which is power supply related could actually be injected into the signal that we hear.

I also believe this is Tom, Frank (I did not call you Fred this time) DF and Terry's observations with their simulations and would appear that both complex impedance and filtering effect of the power supply has some critical effect on the "apparent sound quality" which is of course distortion of some kind or another - probably related to inter-modulation distortion.


Now one final comment, could this be why some speculate that an amplifier with no overall NFB sounds "better" (or one with a non differential input). Or am I just opening another can of worms here. I do believe that we will come to conclusions that will benefit us all.

[AP2]

Originally Posted by tsiros

Has anyone mentioned that the distortion of the amplifier due to power supply ripple, when the amp is driven hard, will be relatively insignificant to the distortion that will coming out of the speakers, which will be driven hard, since the amplifer is being driven hard?

Hi,
this is a topic of fire. anyone, should demonstrate that the sound changes even at low power. but those who are familiar with this problem, use a lot of high flux toroidal, with lot of high low ESR capacitors. this is what you find inside an amplifier from € 20,000, if you open it. so..problem exist!
the solution is very complicate, if solve with low hot.

[danielwritesbac]

Originally Posted by Kindhornman

I have actually seen the exact same capacitors with very name brand wrappers that are identical in every was except for the covering in production. No lie, just a pretty wrapper and a multistrand axial lead out wire and nothing more....

Thanks for that post.
Multistrand cable? In an audio amp? I just said the "f" word. That cable has the copper fibers individually coated slightly for corrosion resist. Why do I want 16 bad copies of my signal distorted like a house of mirrors? Does that help tweeters? Apparently, they are selling tone differences, and they must mark up the price or else call it noise? The durability of the botique polypro caps looks acceptable for speaker crossovers, especially for shunt.

But, I never use expensive tone/noise caps in audio amplifiers.
The sole exception is inexpensive--Cerafine 4.7u or smaller paralleled with a tiny economy polyester cap can be an interesting choice for an input cap, but not in every application.

Originally Posted by Kindhornman

Daniel, Could you do me a favor. At this point I do not care about the name on the cap. List the actual specification differences that are making the changes you are talking about. Otherwise what it appears to be is you are trying every perturbation to try and use an expensive boutique cap somehow. Is that really the point here, or are we looking at specifications and damn the manufacturer of the components?

Except for availability of accurate datasheets, the manufacturer is unimportant. I quoted Cornell Dublier (Mallory) because they provide the most comprehensive data. Compare LP for the high efficiency cap verses SK or SEK for the standard ordinary cap. There is plentiful published data, but I don't really know the cause of the differences. For one thing, LP is good enough to use for an output cap, but SK and SEK are definitely not. The LP works great for any job at the amp board, the SK/SEK works great on the power board. . . or you can turn that example backwards to get some very poor performance.

Originally Posted by Kindhornman

If standard capacitors are giving you a superior result in your opinion why keep chasing this application.

Because, in comparison to the low ESR cap, I want to know if the greater loss of the Standard cap is providing helpful ballast for more easily charging many in parallel at the power board.
P.S.
If I can get a better/faster charge, that looks just like using a bigger/stronger transformer. Right?
But if I have inadvertently disabled/hindered some of the charging, that looks just like using a smaller/weaker transformer. Right?
At the power board, easier to charge wins, but they don't mention it in capacitor datasheets. Do they?

[DF96]

Originally Posted by Nico Ras

I believe that power supply hash is entering via the overall NFB loop

Assuming the NFB loop is correctly implemented, then this means that hash is already in the output so the NFB should be sending it back to the input for partial cancellation. This is what NFB is supposed to do.

It is easy to get the NFB wrong, and pick up ground noise, but that is not the fault of NFB but the fault of the designer. The important thing is to ensure that the input signal and NFB are both referenced to exactly the same ground point.

'Smaller caps mean better bass' might just mean 'smaller caps mean more distortion and more PSU IM, so bass sounds louder so it sounds better even though it is really worse'.

[AndrewT]

Rubbish can enter the amp from the output terminal. This is then injected into the -IN of the LTP.

Dr Cherry suggested a good way of attenuating this cable rubbish.
Tap off the NFB from between the R & the C of the R+C Zobel.

I have rarely seen it implemented. In fact I cannot recall a single instance on this Forum.
I have used it in a couple of chipamps. But, I could not detect any improvement in attenuation of interference. However you all know I use proper filtering on the input and rigorous use of twisted pairs.

[Kindhornman]

Daniel,
In answer to your question these were capacitors that people were using in passive crossovers. They had multistrand leads and were mucho expensive for no real gain in any way. Looked nice but were a real sham as far as any real difference. Thanks for your response.

[DF96]

Dr Cherry suggested a good way of attenuating this cable rubbish.
Tap off the NFB from between the R & the C of the R+C Zobel.

Snag with this is that it introduces extra phase shift, although it might work in some cases. Better to put an RF filter outside the loop.