Fender Brand X X25R combo Hum

[unparalleled]

Has anyone successfully got rid of the clean channel mains hum in this model amp?
I think it is a design problem rather than a fault condition.

[Enzo]

No hum on the lead channel?

Why do you think the amp is designed poorly?

I could see a leaky U1-b or a leaky Q1 introducing some hum. But other than the brief branching right there, the signal path through the rest of the amp is the same for both channels.

[unparalleled]

Only the lead channel. Lead has hiss which is to be expected with that much gain, but no hum.
The + - filter caps are only 47uF and the first TL072 has further dropping resistors to de-couple from the others, (also only 47uF here too).
I added a copper foil screen (insulated) above U1 and it's associated components connected to ground, this reduced the hum a bit.
Don't want to spend lots of time on this amp, it is not worth too much.
I have his other amp sorted, a 70's tube combo made here in NZ.
Just want to get this SS cheapie sorted quickly if possible and he's out of here happy!

[Enzo]

The main filter caps are 2200uf, the zeners are filtered by 47uf, and yes the additional 13v filter stage too.

But that same supply serves both channels, and any power supply hum should show up in both. Besides, both rails ripple ought to be about the same and pretty much cancel.

Adding a shield seems odd, does the chassis not make contact with the foil in the cab? Some amps hum out of the cab because the cab completes the shielding.

Just for science, try removing Q1. yes it will screw up channel switching in that the clean would not go off durning lead, but it helps to determine if Q1 is causing the hum.

I see no reason the one op amp in the clean would be any more hummy than the one op amp in the lead.

Other than teh Q1 thing, put the amp in clean so you can listen to the hum, now ground off the signal path at R14, then R8. Either one kill the hum?

Amd while we are there, does turning the Drive Volume R24 from the lead channel have any effect on the hum while in clean? If so, we could have hum coming in through the Q2 route.