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Author Topic: Ground Loop Problem  (Read 4688 times)

RDV

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Ground Loop Problem
« on: May 07, 2006, 09:35:25 AM »
I've got a ground loop occurring with my subamp which I'm running from an aux out on my Mackie mixer, it goes from there to an active crossover, then into a chipamp into the sub. I disconnected the ground on the signal cable that goes from the mixer to the subamp. Doing this took the hum away from my near-fields but sort of increased it in the subamp, well either that or now that it only comes from there that's how I'm perceiving it, I don't know. Would a 1:1 isolation transformer be the way to go, leaving the signal ground unhooked still? I'd like a little advice before proceding.

TIA

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joecool85

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Re: Ground Loop Problem
« Reply #1 on: May 07, 2006, 09:53:28 AM »
How are you grounding your stuff?  In my experience with chipamps, star grounding is the best solution.  I had a ton of hum in my LM3886 before I grounded that way, it was going through the chassis for input and output signal causing a ton of hum.  Then I re-did it again because I had run wires near all the AC->DC power board and tranny causing hum lol, but just keep your signal wires away from power wires as much as possible, then ground everything at one point.  I actually soldered mine together at one point.
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RDV

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Re: Ground Loop Problem
« Reply #2 on: May 07, 2006, 10:03:44 AM »
My stereo LM3886 amp has 0 noise of any kind but the subamp is another story. It's in a wooden box so there is no chassis ground as such. I did use star gounding techniques building it though. It doesn't hum till I plug it into the mixer. There's a chance I didn't filter the supply for the x-over enough. I'll probably poke around at it later, right now I'm burned out from a 3 gig weekend, but I got a pocket-full of dough so it's all good.

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joecool85

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Re: Ground Loop Problem
« Reply #3 on: May 07, 2006, 10:36:17 AM »
Nice!  3 gigs in one weekend is pretty sweet.  My lm1875 is in a wooden box, so I had to run wires for all the grounds.  The thing is, most of the time its better to ground that way anyway.
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RDV

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Re: Ground Loop Problem
« Reply #4 on: May 08, 2006, 03:51:13 PM »
I had left the ground of the crossover out of the star. I rectified that and got rid of about 75% of the hum. I used one of my multi-output transformers for the x-over/subamp and it just didn't occur to me that I had to ground the x-over too since they were both running off the same transformer. What I didn't get was that this transformer is like 4 seperate in one, each with their own needs.

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joecool85

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Re: Ground Loop Problem
« Reply #5 on: May 08, 2006, 04:50:56 PM »
Ah, good to hear.  I figured it was a grounding issue.  99% of the time thats what hum is caused by.  That or inadequate power filtering.
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