Ampeg SVP-Pro noisy DI out; any ideas?

[kanped]

[color=#000000][font=verdana, geneva, lucida,]Hi there. Recently picked up a second-hand Ampeg SVP-Pro. Gigged it for the first time the night before last, sounded great. At last night's gig however, there was a loud buzz coming from the XLR out. It wasn't coming out of the jack out. Tried changing cables, changing channels on the desk (all the same as the previous night to begin with) to no avail. The buzzing even kept going when the unit was powered off, until the XLR was disconnected (may have been due to capacitors but it shouldn't have been putting out audio with the power off).[/font][/color]

[color=#000000][font=verdana, geneva, lucida,]When I got back tonight, I tried plugging it into my desk at home and it seemed to work fine.[/font][/color]

[color=#000000][font=verdana, geneva, lucida,]The only thing I can think of that would cause this is a grounding difference, since the unit has no ground lift option (I think?). Does anyone have any idea of what might have caused this, or how to fix it? If it keeps happening, it's going to be a serious problem. [/font][/color]

[color=#000000][font=verdana, geneva, lucida,]Also, although the unit has 2 jack outs, it seems as though plugging one in cuts the other off (that's what I ended up doing; taking a jack into the desk but it cut out the sound from my cab). Is that normal? I can't see the point in having 2 of them in that case.[/font][/color]

[Dood]

Yup, sounds like an earth issue and also agree an earth-lift could have helped. The only thing I can think to do is to insert an external DI box in the signal path. I'd suggest if you're not using the effects loop to take a lead from the send in to an external DI as this will pick off the signal including your EQ settings. (Look for a DI with a ground lift switch)

[Dood]

I don't recall one output muting the other on my ole SVPs. I'd suggest something might be up!