Metropoulos Forum

Hi fellas, I've noticed my presence pot and Vol 2 pot make a scratchy noise when rotating them (they are PEC maybe that has something to do with it) even with no instrument plugged in. When playing some times I notice a bit of a drop in level and a higher level of hiss that seems to fall away a second or two after muting the strings, it only realy happens when using level boosting pedals ie fuzz or treble booster. When I first built the amp the problems were more pronounced and there was some crackle in there wich seems to have been fixed by swapping out the pots and more break in time but the prob is still there just a little more intermittent and subttle. I've done a lot of trawling through threads and now have a feeling the prob could be a leaky cap. Unless you guy's have any other ideas. I want to be sure of what I'm checking for. Is it correct that one indicator of leaky caps would be to check all the pot terminals to ground and I shouldn't read any DC voltage? I picked up from one thread to set the meter to DC and measure between the two cap and 220k resistor joints to ground with the stand by on. As I understand it I should see 0v DC. If I see a voltage at either point this indicates a leaky cap? Or is it that I should see a - bias voltage and if one has a reading leaning twards + or 0v that's the leaky cap? There was another bit about checking between the two cap joints (i should also see 0v DC?) but I didn't understand what this would tell me. Also, how do I test the other caps? What am I looking for? Any advice would be greatly apreciated.

Ok, I've taken some readings but I'm not 100% if everything is OK. It's a stock 69 circuit. With the stand by on I checked all the pot terminals to ground and only found 13Vdc on the neg feed back wire on the presence pot. I then checked all the mustards to ground on the valve side of the board, they all had various voltages on them. I then checked the mustards on the controle side of the board. The only voltages I found was 13Vdc on the .1uf and -44Vdc (bias voltage) on the two .022uf conected to the 220k splitter resistors. I had 0Vdc between the two caps. On the valve side of these two cap's, to ground I had 220vdc on one and 212vdc on the other. There was a difference in the splitter resistors K ohms resistance, 225K and 221K don't know if thats a problem? Does it sound OK or not?

Perfectly normal to get some DC on the presence pot of a 5k/0.1uF set up. If you use a 25k/4k7 combination that will stop it, who adjusts the presence mid set anyway?

Cheers mate. Much apreciated.