JMP 2203 Low Input Problem

HHwarner

I seem to have a problem with the low input on my JMP 2203. There is a lot of ear piercing squealing and hissing with very little guitar coming through. High input is working fine. I’m not sure how long it’s been an issue as I’ve never used the low input before. I’ve tried swapping pre amp valves but makes no difference. I don’t think it’s a valve issue as the high input works perfectly. Anyone have any ideas what it may be?

Modulus_Amps

If the high input works fine then the circuit and valves are fine, So my guess is a bad jack socket, possibly the result of no use for years. Doesn't really explain the squealing though??

HHwarner

I’ll try some contact cleaner in the input

HHwarner

A bit of an update, I’ve tried cleaning the input to no avail, it sounds like I’m tuning a radio in as I rotate pre and master volume knobs so guessing something a bit more serious. High input is still fine though
https://imgur.com/gallery/YY6qL7O
TMB controls also make it sound like tuning a radio also

ICBM

Sounds like probably a broken ground connection on the Low jack. As Modulus_Amps says it can't be anything more serious, because the signal from the High input and first gain stage actually passes through the Low jack on its way to the second stage. Unless the amp has been modded in some way...

HHwarner

Yes you got it, ground wire from the high to low input come away. Thanks for your help guys