Now, I'll be the first one to admit that this is one heck of a cheapo amp. But it still does something really odd:

It only works when I reverse polarity on the RCA inputs (made special adapters for that purpose). With reversed polarity, it works fine except for some ground-loop noise that I will debug with the help of Tonys FAQ. But with proper polarity the noise gets worse and there is absolutely no signal coming through.

Any one want to take a gues what's up?

Armin

Do you have (a) another way of checking whether the outputs from the empeg are good, and/or (b) another line-level source to plug into that amp to see if it's the amp's fault?

(You need to narrow down the source of the problem via a process of elimination.)

Also, are the cables running to the amp damaged anywhere along their length (such as a sharp metal edge cutting them), or are they touching metal somewhere so that their shrouds are grounded to the chassis?

Also, have you checked to see if the wires have pulled out of the back of the sled? Some docking connectors had that problem.

Hi, Tony,

I was away for a day, thanks for your reply!

The empeg is known to be good. It worked with a different amp that I gave to my girlfriend. I just removed the old amp, plugged in the new one and - nothing! Only after playing with things I discovered the "reversing" trick. It didn't make any sense to me, but hey, it worked!

I won't have time for serious troubleshooting until later. It works for now. The ground-loop-noise is barely noticable as long as I leave the gain on the amp turned down.

Armin