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Old 6th January 2013, 01:53 AM   #1
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Default 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??
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Old 6th January 2013, 03:01 AM   #2
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Is there any DC voltage or significant AC noise on the RCA shields of the amp?
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Old 6th January 2013, 04:10 AM   #3
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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
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Old 6th January 2013, 04:28 AM   #4
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What is the amplitude of the noise on the shields?
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Old 6th January 2013, 04:38 AM   #5
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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
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Old 6th January 2013, 04:49 AM   #6
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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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