Bypassing 1st and 2nd Cap in Power Supply

[serpent68]

Is there any benefit in bypassing the 1st and 2nd capacitor in the power supply?  I have a couple of 1uF film caps lying around and wonder if there is any sonic benefit in doing so.  I have already bypassed the 3rd power supply cap with a Mundorf Supreme.

[Grainger49]

I would, and have, bypass the last (in this case 3^rd) cap in the power supply.

That is the biggest bang for the buck.  There will be a slight improvement bypassing the 2^nd cap in the power supply.  But that difference will be much more subtle.

[Paul Joppa]

Is there any benefit in bypassing the 2nd and 3rd capacitor in the power supply?  I have a couple of 1uF film caps lying around and wonder if there is any sonic benefit in doing so.  I have already bypassed the 1st power supply cap with a Mundorf Supreme.

Sounds like a really easy experiment to try - then you can tell us if there's a benefit!

[serpent68]

Is there any benefit in bypassing the 2nd and 3rd capacitor in the power supply?  I have a couple of 1uF film caps lying around and wonder if there is any sonic benefit in doing so.  I have already bypassed the 1st power supply cap with a Mundorf Supreme.

Sounds like a really easy experiment to try - then you can tell us if there's a benefit!

Yeah, it should be an easy experiment for most, but based on my mediocre soldering skills it will be a risky task... Hope I don't break anything in the process

[Paul Joppa]

That's what clip leads are for!  :^)

[Grainger49]

Always try bypass capacitors with jumpers first.  That allows you to make the decision by comparing with and without easily.

Then when you decide to put them in, solder them in.

[Chris65]

Haven't tried this. What would be an appropriate value to use at the 3rd PS position?

[JamieMcC]

I used 2.2uf when bypassing mine 

[serpent68]

Apologies, I meant to ask about bypassing the 1st and 2nd caps in the power supply, but got the numbers wrong and asked about bypassing 2nd and 3rd caps.  I've corrected the title and my original post.

Anyway, I've tried the bypass in the 1st and 2nd caps with Jantzen Superior 1uF.  Result is not good.. I hear smearing in the mid-bass region, and the sound is more sloppy overall.  Have run it in for more than 48 hours now, the sound does not seem to improve.  I'll remove the bypass caps tonight.

Bypassing the 3rd cap (with Mundorf Supreme 0.68 uF) did bring improvement though.

[Grainger49]

The closer the power supply cap is to the audio circuit the more important it is that the cap be able to release its voltage quickly.  That is what a film cap will do, release the voltage faster than the electrolytic. So the first cap after the rectifier diodes is least important. 

Another reason for a film cap in this position is an AC (signal) return to ground.

In the Crack there is a CRCRC filter.  Let's think about what the first cap after the diodes sees.  It looks just like a sine wave except the negative wave has been inverted.  It looks like a first grader's depiction of a mountain range.  It is just a series of humps.  The first C and R work together to start leveling that and start smoothing out the humps.

Then the second C and next R smooth that to close to flat DC.  There is a little ripple left.  That is what the final C flattens out to a good smooth DC.

I would put most of my money in getting a good film of the largest value to bypass the third cap.  Then a much smaller film cap on the second cap.  I wouldn't bother to ever bypass the first cap.

[serpent68]

Thanks Grainger. 

So for the 3rd cap, the larger capacitance the better?  I only have a 0.68 uF, so its a really puny cap.  What's the effect of using a larger cap, say a 2.2 uF?

[Grainger49]

Yes, the larger the better, film or electrolytic.  Using a larger film cap gives more instantaneous energy to the tubes themselves.  Some designers put a local film cap (energy storage) right at the plate load resistor on the circuit board.  In the case of a cathode follower (no plate load resistor) the cap is attached to the plate and ground at the tube socket.

I'm only guessing here, but a larger value . . .   say Dayton 59uF ($13.80 at Parts Express) might have greater impact than a 0.68uF Mundorf ($55.40 at Parts ConneXion).  You might even bypass the 50uF with a 0.01uF Audiocap ($4.91 at Parts Express) and be better off.

But if you have the 0.68uF by all means get your alligator clip jumpers out!

[serpent68]

Great!  I'll try to parallel connect the two 1uF Jantzen Superior to the 0.68 uF Mundorf first to see if there's improvement.  That makes 3 parallel caps bypassing the 220uF electrolytic.  I hope that is ok.

I read somewhere about a 1% rule for bypass capacitor value.  I'm guessing that it apply to coupling / output caps only, and not to power supply filter caps where bigger = better.

[Grainger49]

I'd try them one at a time and all combinations.  That is what jumpers are for, well, that and other experiments.

Yes, the 1% is often used but is not a law of Physics, just a suggestion.  It does apply to all bypassed capacitors, if I remember well.  I have done both and probably never hit the 1% on the nose.  I've done just what you are going to do, I used capacitors on hand.