Power amp hum

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Z-Plane
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Power amp hum

Post by Z-Plane » Thu Sep 15, 2011 2:13 pm

I just got a power amp out of the cupboard to run some passive monitors, its a cheap 400w disco amp with unbalanced inputs. I was getting a monster 50hz mains hum and after much hunting found the culprit - it occurs whenever both inputs share any kind of electronic connection. I began the hunt going through my rack and ended it with a dynamic mic plugged directly into one amp channel, its nice and clean until you connect the link. No difference if its tip, shield or ground lifted - big hum on both channels. I should probably throw it out, but its actually quite clean in isolated mono and plenty powerful enough with a quiet S/N ratio. What is going on here and is there any fix worth attempting?

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Scodiddly
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Post by Scodiddly » Sat Sep 17, 2011 5:36 am

My Google search for "cheap 400w disco amp manual" didn't find anything. What brand/model is it?

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Z-Plane
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Post by Z-Plane » Sat Sep 17, 2011 5:00 pm

Thanks for the reply its a KAM MDJ2, which probably returns even less useful information than cheap disco amp. Usual budget innards from what I can see and I was curious if the mono=clean/stereo=hum issue had a general earthing test or fix I could perform.

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Scodiddly
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Post by Scodiddly » Sun Sep 18, 2011 9:31 am

Hmm... OK, I didn't look up the manual, because (like you say) it probably won't help any.

I'd suggest looking at the power side of things. Make sure the grounding makes sense, make sure the power cable is correctly wired.

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