6G2 Clone - buzz when volume at 0-2

[fdesalvo]

Hi, all.

Happy Monday. I'm almost finished debugging a customer's 6G2 clone and am down to two remaining issues:

1. Buzz when volume at 0 - 2 + tone at 0-9
2. Non functioning trem


My main concern is issue #1 at the moment. I found and corrected a host of assembly errors and now the amp is nearly silent, save a little hiss at volume, but there's buzz aplenty when the conditions of #1 are met. I can nearly silence it by touching V1B's grid wire with my finger. After running shielded cable here, no improvement was noted. Layout is mainly old school fender with a hoffman ground scheme at the pots. All tubes good. Issue disappears with V1 pulled.

TIA

[Enzo]

Good photo might help. Schematic you used. And really, I have no idea what a Hoffman ground scheme is.

So it buzzes volume on 0-2. What happens as you turn it up further? Doe the hum just fade lower? Does the hum cut off like a switch at higher settings?

[fdesalvo]

Hey, Enzo - thanks for stepping in.

Disregard the grounding scheme. The buzz turns on and off like a switch from either the tone or volume pots.

[Jon Snell]

It is very important on a clone build to ground each point correctly as I explained in answer to your question on TDPRI. The hum comes from the control grid ground point on the 7025.
Did you correctly place the ground points and what was the outcome?

[fdesalvo]

I removed the ground bus and tried a few different ground points and there’s a strong oscillation now. Sounds like a cap charging and discharging. I should probably just test this amp down and rebuild it from scratch. This is probably the last clone debug I do for a while. The way he wired it, there’s no way to chopstick.

[fdesalvo]

Alrighty. I've gone through and verified all connections and grounds. preamp and 3rd filter cap ground at input. Noise can be modulated or turned on or off by playing with intensity and speed pots, as well.

[fdesalvo]

The builder is using a switching 1/4" jack for the trem fs. when I break ground, the oscillation stops.

[g1]

How do you mean, break ground? Disconnect the footswitch jack? Or is it a switched type jack that shorts to ground when nothing plugged in?
It sounds like there are 2 separate issues now, the buzz/noise and the oscillation/motorboating? Or is is the oscillation/motorboating the now working trem?
When you said the trem controls affect the noise, do you mean the buzz or the oscillation?

[fdesalvo]

Sorry I haven’t been clear. There are def two issues. The main issue now is the motor boating. There is a switched footswitch jack that’s doing its job grounding the signal with nothing connected. If I remove the ground, the motor boating stops and the trem functions, though it’s incredibly noisy and flatulent lol. I'm going to remove the ground link on the switch and have its function mirror the jack on the schematic. Will report back soon.


BTWFor giggles I’ve shielded all grid wires and the intensity and speed controls, which alter the pitch of the motor boating.

TY!

[fdesalvo]

All issues resolved. It was the erroneous wiring of the foot switch jack. I installed a non-shorting jack and all issues went away. Thank you all so much what a great learning experience.

[g1]

Weird but glad you got it sorted out. What happens now if you use a footswitch, all ok?

[fdesalvo]

It's too much for my fragile mind to bear. Sounds normal with footswitch in use.