1978 2203 alternate grounding - slight power drop?

[MikeO]

Hey guys

I've got a bastard 2203 that I rebuilt with a metro 2203 board kit (I had to, original pcb was modded badly with many burned and lifted tracings).

Anyway, it's worked fine for years. I decided to replace the pots (cts) and do the alternate grounding as found here:
http://home.comcast.net/~mamp17/index.html" onclick="window.open(this.href);return false;

I also changed the tone stack from 33k/500p to 56k/250p.

The amp sounds alright but it seems like it lost some power. Did the alternate grounding do this or did the tone stack change do this?

Negative feedback setup is 100k on 4 ohm tap and I run the amp thru a Matchless ES412 open back 4x12 that's wired for 8 ohms.
(Amp is set to 8 ohms) Thanks for any help you can provide!

[herbvis]

Changing the tone stack to 56k/250pf will thin the tone out. I may be incorrect, but with a 33k/500pf tone stack, the PI output caps are usually a .022 value in marshall amps. And a 56k/250 tone stack usually have .1 PI output coupling caps. Assuming your pi output caps are .022, you may be able to change them to .1 and thicken/balance the amp up.

[MikeO]

Thanks! I forgot to mention that I've got .047 mustards in that spot.
I think adding .1uf caps will make the amp mushy. It's already on the verge. I'll go back to the 33k/500p and see if that cures it.

[MikeO]

That did the trick, thanks! I had no idea the tone stack could effect the output that much.

I guess thanks to the alternate grounding, the amp sounds better than before.

I used a 1/2w cc 33k and a polystyrene 560p. I also replaced the .1 on the 5k presence pot with an old tropical fish .56uf cap.
I am now Very Happy

[herbvis]

Glad I could help