values of ground(?) coupling caps in Aikido

[cbutterworth]

On my stereo Aikido Octal (6SN7) PCB from John Broskie, there are two caps, one labelled C5 and the other C6. Both of these connect to ground, C5 is directly to ground, whereas C6 goes to ground via the "nulling" resistors (R15 & R16). In the PDF that I used for assembly recommended values were:

C5 1-10uF, I am using 2.2uF here
C6 0.1uF, I am using 0.1uF here

In a later version of the PDF, the values are a little different for C6 0.047uF to 0.22uF.

Now, I have a little 120Hz ripple on the audio output, it is very, very quiet, and I want to reduce it as far as possible before I go to regulated B+. Sy has suggested a trimpot for R15 for fine tuning.

QUESTIONS:

Q.1. If I increased C6 from 0.1uF to 0.22uF could that help in reduction of the 120Hz ripple?

Q.2. What would be the effect of increasing C5 (currently at 2.2uF) to 10uF?

My B+ sits at around 350VDC and PSUDII models ripple at something like 0.6mV. I am thinking of changing out my filter caps (after chokes) to 80uF and 160uF, they are now at 60uF and 80uF. However, the current ones are motor-run caps, and a change out to larger values may require electrolytic caps due to their smaller size. BUT, don't electrolytic caps have an effect on sound?

Thanks,
Charlie

[Sheldon]

Originally posted by cbutterworth
On my stereo Aikido Octal (6SN7) PCB from John Broskie, there are two caps, one labelled C5 and the other C6. Both of these connect to ground, C5 is directly to ground, whereas C6 goes to ground via the "nulling" resistors (R15 & R16). In the PDF that I used for assembly recommended values were:

C5 1-10uF, I am using 2.2uF here
C6 0.1uF, I am using 0.1uF here

In a later version of the PDF, the values are a little different for C6 0.047uF to 0.22uF.

Now, I have a little 120Hz ripple on the audio output, it is very, very quiet, and I want to reduce it as far as possible before I go to regulated B+. Sy has suggested a trimpot for R15 for fine tuning.

QUESTIONS:

Q.1. If I increased C6 from 0.1uF to 0.22uF could that help in reduction of the 120Hz ripple?

Q.2. What would be the effect of increasing C5 (currently at 2.2uF) to 10uF?

My B+ sits at around 350VDC and PSUDII models ripple at something like 0.6mV. I am thinking of changing out my filter caps (after chokes) to 80uF and 160uF, they are now at 60uF and 80uF. However, the current ones are motor-run caps, and a change out to larger values may require electrolytic caps due to their smaller size. BUT, don't electrolytic caps have an effect on sound?

Thanks,
Charlie

I doubt that a change in cap size for C6 and C5 will make much difference, but rather than rely on speculation, just try it. As you want to increase the capacitance, you don't even have to heat up the soldering iron. Get out your clip leads and clip in capacitance in parallel with what you have there. Listen, yes, no? - you will have your answer. Do the same with the caps after the choke.

If the issue is in your grounding scheme, changing the power supply caps won't solve the problem. If the grounding is fine, then SY's suggestion may be the call. If you don't solder the pot onto the board, but use clip leads for testing, be very cautious to keep fingers and tools away from hot leads.

Sheldon