Roland jazz chorus 50 distorting at low volume

Hello everyone.

I’ve got a Roland JC50 that’s acting up. To be more precise it’s distorting all the time. No matter what volume I play at. If I play louder the distortion gets “hidden” behind the guitar sound but when played softly it’s very audible. There is clean guitar signal but also a distorted signal in the background. If I don’t play the amp is pretty silent.

Any idea what might cause this? I’m thinking maybe a faulty transistor but I don’t know which one.
I also have an idea that it might be a film capacitor since if I touch it, it makes a kind of “magnetic” sound thru the speaker. Maybe this is normal?

Any help much appreciated.

I had that problem with a capi love child eq.  It was  a transistor in the eq.  An O scope is your best friend .  Put a signal in and trace signal through.  Turn volume  till u hear the distortion and follow signal sine wave till it shows distortion in path and then backup.  The circuit before could have a bad tranny .

Other problem is D.C. From a leaky cap will bias the stage incorrectly and force it to clip one half of the waveform prematurely.    Meter can test that but a scope is handy to see it.    Schematics are on web for jazz chorus.

Wow! Thanks so much for the fast and thorough reply. I’ll try the scope. Some time is gonna be the first, right?

Could also be a bad speaker.  This can be caused by the coil rubbing inside the magnet.  It'll still pass signal okay but you get that extra distortion, even at low levels. Is it possible to test it through a different speaker cabinet?

There is a headphone jack. I’ll start there. Thanks Matt C!

check AC voltage on first filter cap(s).

It was the speaker. I tried it thru the headphone jack and it’s clean as a whistle.
Thanks err’body for the suggestions