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Ground Loop Problem

Started by RDV, May 07, 2006, 09:35:25 AM

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RDV

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

RDV

joecool85

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.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

RDV

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.

RDV

joecool85

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.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

RDV

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.

RDV

joecool85

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.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com