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Old 28th February 2002, 04:10 AM   #1
JoeBob is offline JoeBob  Canada
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Default Static from an RCA connector?

I just added two more channels to my amp (7 instead of 5, decided to actively bi-amp the main left and right). I tested the two channels before installing them into the chasis (I used a test power-suply I built), and they sounded fine. By the way, they're LM3886 circuits. But now that I installed them, one channel is clear as day and sounds nice, but the other has intense static, like old TVs would make when tuned to a station that didn't exist. When I have the RCA cable disconnected it's not there, but when connected the static appears.

I just finished my ground-loop problem, and now this comes up, dang it. Just wondering if it could be the RCA connector, or if somehow my circuit got damaged...
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Old 28th February 2002, 06:42 PM   #2
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Default groundloop?

sounds almost like u have made yourself a groundloop maybe.. try to separate the body of the rca-connector from the rest of the chassis and connect the rca-shielding with a 100nF capacitor to ground and see if it vanishes..
Good luck.
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Old 28th February 2002, 09:56 PM   #3
JoeBob is offline JoeBob  Canada
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I'll try, but it's strange how all my other identical channels don't bahve simmilarly...
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Old 28th February 2002, 10:11 PM   #4
paulb is offline paulb  Canada
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Could the one channel be oscillating? Check your stuffing carefully to make sure all the parts values are what you thought they were.
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Old 1st March 2002, 02:07 AM   #5
JoeBob is offline JoeBob  Canada
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I checked and ya, my values are what they're supposed to be. But I just noticed something really strange, when I connect the RCA connector to that one channel it goes static, but when I connect an RCA connector to any other (except one), the static goes away (but there's still crackling, barely there, but very annoying once you notice it)... I have absolutely no idea where this is coming from, the only thing in common with the two RCA connectors is that they share ground, but the ground is connected together (I checked) so it's not a cold solder joint or something.
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Old 1st March 2002, 04:08 AM   #6
JoeBob is offline JoeBob  Canada
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Well, I have no idea why this is happening, I even tried to replace the RCA connectors, with no luck.

But it turns out that crackling only happens in the highs, none below. And since I'm going to use it for bi-amping (both bass & mid/high amps are identical) I could just use it for the bass (where I don't hear crackling). But my question is, is that alright? Or will it eventually fail, although it'll only do low frequencies, (where it seems to preform identical to the others)?
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Old 4th March 2002, 05:09 PM   #7
JoeBob is offline JoeBob  Canada
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I checked, one of my channels has DC on the output, but as soon as I connect an RCA jack, it goes away (maybe the grounded shield on the wire, or something, I dunno). And my other channel is fine, until I plug something in and then I get DC on the output, but before I was only testing that one, it turns out once I plug it in DC appears on all my outputs, how is that happening? The only thing they have in common is ground...
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Old 4th March 2002, 06:32 PM   #8
paulb is offline paulb  Canada
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JoeBob, how do you know it's DC on the output? Are you using a multimeter or a scope?
I still think it could be oscillation. When it comes and goes by connecting an input cable, it sounds suspicious to me...
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Old 4th March 2002, 10:59 PM   #9
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I checked with a multimeter, not a scope unfortunately. I doubt it's oscilation, because I did all the precautions to avoid it... But if it is, how would I check?
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