Vibro Champ footswitch issue

[JSett]

Odd one here, I could use some advice.

A while back I changed out the footswitch RCA connector in my Vibro Champ for a regular 1/4" jack while I had the chassis out for something else.

Now just using a regular fender single switch, when the vibrato/Tremolo is disengaged, the amps overall volume goes down as the intensity knob is turned up. Like the signal is being shorted to ground.

Now, the original RCA socket was just chassis mounted with one blue wire to the tip. The 1/4" jack is just in the same hole and with the same blue wire to the tip.

What gives??

[ziess]

Assuming it’s a non-shorting mono jack it shouldn’t have any impact on the circuit. Does it still do it with the footswitch cable removed?

I’d start by looking at the bypass caps and resistors on V1 and V2.

Tommy.

[JSett]

Assuming it’s a non-shorting mono jack it shouldn’t have any impact on the circuit. Does it still do it with the footswitch cable removed?

I’d start by looking at the bypass caps and resistors on V1 and V2.

Tommy.

Nope, works absolutely fine with no footswitch.

Caps and resistors all good, literally went through everything the other day giving it a service. I did the swap ages ago but never really bothered to use it. It's basically acting as a secondary volume control.

Google has thrown up dozens of people with the same issue all around the world on various forums over the years so it's obviously something that is a known thing to happen. Annoyingly, no threads I've found ever seem to mention the fix