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S Merlington 6th January 2013 01:53 AM

Alpine MRP-M500
I got another one of theese in..

Amp powers up and plays but the guy told me if u plug in the rca jacks to the amp it acts like its back feeding up the rca's into the head unit and the door speakers start having really bad static comming from them..

As soon as u disconnet the rcs jacks from the amp the static goes away ..

I can get the amp to do this on the bench as well..

Any ideas??

Perry Babin 6th January 2013 03:01 AM

Is there any DC voltage or significant AC noise on the RCA shields of the amp?

S Merlington 6th January 2013 04:10 AM

I have 0.42 volts on the RCA Jacks Using amps fround terminal as reference..

And yes i see AC noise on the rca jacks

Perry Babin 6th January 2013 04:28 AM

What is the amplitude of the noise on the shields?

S Merlington 6th January 2013 04:38 AM

Not sure how to tell but it i set the scope to 20MV .5 ms and center the trace the noise will go up to the line that say 90 2 lines above the center line

Perry Babin 6th January 2013 04:49 AM

That's insignificant. If it was the amplitude on one of the windings on the transformer, that would be a problem. The low level noise that you're seeing is common on many amps.

Are you sure that the shield ground for the head unit is intact? It could be that an open shield on the head unit is causing the amp to produce a lot of high frequency noise and that's affecting the head unit's output.

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