2. amps-preamps
  3. 1236409165

Strange ground loop...?

Hey,

I just hooked up a new amp and I'm having a strange noise issue. Only in my right channel, I get this high-pitched whine... maybe around 2khz. My left channel is dead silent.

The problem seems to be an interaction between my DAC and my amp. If the DAC is off, the amp is silent.

The amp is an 84' yamaha, so the cord has no ground. There is a ground screw, though, and I have connected that to my power conditioner, hoping this would solve it... nope.

I've tried plugging the amp straight into the same outlet that the power conditioner is plugged into (into which the DAC is plugged in). That actually did work... but I don't want to run my amp straight into the wall.

I suspect I just need to find a proper place to run that ground wire...

Any ideas?
djembeplay
djembeplay OP
169 posts
 
Jea48 - Your on the right track.

I just hooked up a long run of crappy RCA cable from the analogue outs of my PC. It was the same set-up just with a different source than the DAC... and there is no noise or distortion at all.

So... the problem isn't the cables, but rather something with the output of the DAC interacting with the pre-amp.

It's weird that the DAC sounds excellent when going straight into the AMP.

So, Tvad - I'm going to take your advice and try to ground the DAC to the pre-amp. What is the best way to do this? There is no 'ground' provision on my pre-amp or my DAC, unfortunately.
kijanki's avatar
kijanki
3,575 posts
 
"I just hooked up a long run of crappy RCA cable from the analogue outs of my PC." - quality of the cable is probably not important but this crappy cable probably doesn't use shield as return. Try the same cable from the DAC.
djembeplay OP
169 posts
 
You got it Kijanki.

That sounds perfect now. Man, that was crazy.

Ok, so... for some reason I can run LC-1 from my DAC directly into my amp without a problem... but I cannot run LC-1 from my DAC into my pre-amp.

I would have never guessed this... how weird. I had to try a thousand different things to figure this one out.

So, why would this be the case? I'm pretty clueless on this one.
djembeplay OP
169 posts
 
It was caused by the LC-1 using shield as the return? What does this mean? Why was it bad only when connected to my pre-amp? What types of cable should I be looking at as a replacement?

Thanks everyone for the help - much appreciated.
kijanki's avatar
kijanki
3,575 posts
 
Djembeplay - I'm still not sure that cable was the problem. In general using shield as return is a bad thing but in case of hum or interference we enter the area of "black magic". Bob is right about your problem originating in unit being plugged into different outlets but the certain cables can exaggerate this effect. Why can't you plug everything to the same outlet?
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