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In Reply to: RE: 6800uf across op amp PS pins? posted by Tweaker456 on January 03, 2017 at 08:34:32
That's way too much capacitance to place right at the opamp PS pins. You might see that much filter capacitance or more within the power supply itself but not typically right at the opamp +V and/or -V pins.A modest amount of bypass capacitance can be added where the power supply leads enter the printed circuit board assembly, perhaps 10uF - 100uF. And then a much smaller amount of bypass capacitance right at the opamp PS pins, typically 0.1uF. More is not better because the larger capacitors and their internal inductance offset their effectiveness at bypassing higher frequencies. You'll sometimes see a slightly larger capacitor in parallel with a much smaller one as their undesired inductance is reduced while their respective capacitance values can cover a wider bandwidth for bypassing.
Power supply decoupling is similar to bypassing but the focus is on minimizing signal transfer between stages. A small amount of series inductance can be used comprised of a ferrite bead over a short length of buss wire that feeds -V & +V right at the opamp pins. Different ferrite materials are effective over different frequency ranges. Charts are available from ferrite manufacturers.
Of course audiophiles will go overboard thinking that more is better everywhere. For practical purposes none of this is all that critical until you're in the RF range, using very high bandwidth opamps that are inherently not very stable, and involving high transient currents.
Edits: 01/03/17Follow Ups:
Abe, Maybe you can post about this at the Tweakers Asylum. The thread is near the top and has three op amp numbers in the title. I did just read a tutorial that said like 20 to 50uf with small bypass, so it looks like the person who told me 10-20 was a reasonable person and the person who said they would laugh when I saw smoke would not get a chance to laugh. My post on the subject is titled "10-20uf across op amp PS?" in tweakers asylum. Thanks, T456
Edits: 01/03/17
I learned a long time ago that one can be banned from a forum even if correcting a blatant mistake or the spreading of misinformation. I'm not talking audiophile opinion here, but absolute right vs. wrong. It's happened to me a few times. So for the most part, I just chuckle under my breath now and let some myths and morons live on. I did post a very short question to Tweakers, awaiting a response.[Edit]: This sort of bypass shown below is not uncommon. But I have never seen anyone put anywhere near 6800uF at each opamp +V & -V. Silliness IMHO.
Edits: 01/03/17
Silliness or not I am guilty of being in the bigger is better crowd. It's clear that bobwire is getting away with it, it is not blowing up anything. That's what I'm worried about. Otherwise I would love to try it on the output of my dac. So, will or can it damage the equitpment, catch fire, blow up? If not I'd do it. T456
Putting huge capacitance directly on an opamp -V & +V pins will not damage it but the effectiveness of such a large cap in that location is questionable.
I'm not sure what you mean by "try it on the output of my DAC". If you're talking about the -V & +V pins on the opamp(s) in the output stage of your DAC, that's probably fine..... but not at the audio output jacks of the DAC.
Enjoy!
V- V+ at the chip is what we are talking about. You and another person I believe says it is no problem. A suggestion of a high quality film cap has been made as opposed to a large electolytic. There is very little current there so it does seem another possible reason why it might not make much or any difference. Still, the proof is in the pudding, as us old timers say. Thanks, T456
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