Some Issues with new Plexi Clone

[rexindigo]

Hi There,
I've just finished my Plexi Clone Project (all Homebrew, no kit) and it sounds incredible so far, but
there are some things I'm still not happy with and I hope that the experts in this forum can help me (as always: ampage is the best!):

- My build is extremly sensible to mechanical actions: plugging in a Guitar Cable is very loud even when volume is turned down to zero, and switching of standby makes an awful noise even when volume is turned down to zero
(Tubes are not microphonic)
- normal and bright channel can not be fully closed, there is a little sound even with the pots turned to zero
- With Humbucker Pickups there is litteraly no hum present, but single Coil Pickups seem to be humming much more than with any other amp i own.
- without guitar cable attached there is hum (not the Motorboating type,when there is no ground connection, I have the 1M Resistor to ground there) thats gone with a cable.

Any suggestions?

I used the 1987 Schematic and the hoffmann amp layout but I did change it:
- I extracted the complete Powersupply Cicuit onto one board and the rest (lets call it Signal path circuit) onto a second board (In the Hoffmann layout Filtercaps are more or less integrated into the Circuit board )

[cbarrow7625]

Do you have a switching input jack?

When no cable is plugged in, the grid of the first stage should be shunted to ground by a switching input jack.

How are you grounding your volume pots? Directly to the chassis? Brass ground buss? Ground wires? It sounds like you just don't have a good solid connection to ground from your volume pots.

Chris

[loudthud]

Try the "chopstick" test. You need some type of well insulated stick to tap each component and connection to try to find a bad connection or component that is sensitive to mechanical movement.

[rexindigo]

Thank You Chris, Thank You Loudthud,
Your replies were very helpful:
- first i checked all involved parts (actually every part of the amp) with the chopstick test, just to find out that there was no part that was sensitive to mechanical movement
- then I redesigned the ground connections of the complete front panel components (pots and jacks) including the switching jacks tip to ground when nothing is plugged in, and the result:
The noise is gone (well, most of it, i redarranged the heater wires on the CF tube as well and this added releave for my ears)
Singel Coil pickups are not to noisy anymore and with my battered Tokaj Strats neck pickup it just sounds like "red house"
So thank You for Your help, this was perfect, ampage rules!