FX Loop Problem

[alteredsounds]

I'm using a 5150 combo for most pub / club gigs and love 'em or hate 'em, it does exactly what I need. Problem I'm getting is whenever a cable connected to a pedal is put in the return of the fx loop I get a wall of background hiss, ie. fx return connected to output of decimator, nothing connected anywhere else and wall of hiss.

 

Power is a Dunlop Brick, unplugged everything except the ISP.

 

{censored}ty pre-amp valve? (one is for the fx loop).

 

Cables are all La Grange with neutrik jacks.

[alteredsounds]

anyone? b4 i have to cross-post

[Gorgon90]

Not having any personal experience with the amp, is the line level right?

Generically, rack processors work best at a different line level (-20db I think?) to pedals. Possibly the fx loop is set to work with a rack effect as opposed to pedals and this extra gain is creating noise when you plug the pedal in.

Is this a recent problem after it's worked fine before or the first time you've plugged pedals into the loop?

[alteredsounds]

Hi, the fx loop on the 5150 works at intrument level and isnt switchable to line. It doesnt mater what I connect the return jack to pedalwise, just connecting it to something introduces this noise. Obviously the power amp is going to seriously amplify anything coming back on the return, but I just dont get where the noise is coming from. Mains hum or rf interference I'd be able to tell, but hiss baffles me.

[Gorgon90]

In that case, it won't be the line level.

What happens if you just put a patch cable from send to return?

If you still get the hiss/noise then, it proves it's nothing to do with the outboard, and is something in the amp. In which case it's time for a visit to the local tame electronics/gear fixing guy.