Reverb Hum

[woodrow]

Hi there,

New to the forum! I have a tech question. I have a yamaha Pacifica
guitar through a Fender Princeton 112 amp, and I'm getting a constant
hum when I turn on the reverb with the foot switch. Is there a way to
elimiante this hum? Troubleshooting?

Thanks in advance!

[Adicted to Tubes]

The reverb works without hum when you don't use the footswitch?If thats the case,you have a footswitch problem.
Unplug the footswitch and listen for the noise.

www.claramps.com

[woodrow]

The Reverb can only be turned on by the footswtich. However when I turn
it on, there is no hum until I plug in a patchcord to the amp - Then the hum increases as I turn up the reverb dial, really loud at ten -

[mhammer]

In a lot of amps, the reverb footswitch essentially grounds (to cancel) or ungrounds (to enable) the input of the recovery stage after the reverb pan. If the hot cable tied to the recovery stage's input is not well-shielded for the whole of its length, then it can pick up stray hum when the footswitch unit is situated near a source of hum.

If I am looking at the right schematic, though, thereverb switching in the Princeton 112 does not work this way. Rather, the wires going out to the footswitch unit do NOT carry any wires directly tied to the audio path. What this suggests to me is that the shielding of the cables connecting the reverb pan to the rest of the amp has been compromised in some way. That might be from bending, and it might be the completeness of shielding going to the input of the pan, or coming from the output of the pan.