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schmalex 19th December 2006 11:49 PM

Help, my refrigerator is interferring with my Amp
I live in a small apartment, with what is apparently subpar wiring. I recently completed my 3886 amp. It sounds fantastic, but everytime the refrigerator turns on in the other room, there is an audible pop through the speakers. Likewise, when the electric stove is on, I can hear the element cycling on and off. Also, if I charge my ipod with the AC adaptor and plug into the amp, there's a LOUD hum. When I unplug it from the AC, the hum goes away.

I knew I had problems with a clean electrical line before. My subwoofer is plugged into the same wall and it makes a slight hum too, apparently from a grounding issue.

I've tried plugging the amp into different outlets, a decent quality separate power strip. I suppose I could move the amp to the other side of the apartmet - maybe a different circuit? - but that would make it less user friendly.

I'm quite sure this has to do with grounding, but what do I do about it?

PS - I know this question has been answered in some form or other, but I've tried searching and can't locate the answer. Thanks.

gmilitano 20th December 2006 12:19 AM

You can try an EMI filter or an isolation transformer.

Leolabs 20th December 2006 01:14 AM

You may need a input RF filter too.

MikeW 20th December 2006 01:22 AM

What kind of power supply are you using? Do you have some bypass caps? I had the same problem with noise. When I put a .1 uf. if parrallel with the 36000 uf of caps it seemed to help. This power supply as just a 30A bridge rectifier with a c-r-c-r-c. It was not snubberized.

BrianDonegan 20th December 2006 02:35 AM

I would first ask how you have it set up now. Power supply layout, grounding, etc. There may be something simple that will reduce the problem (don;t know what until we know more though). But maybe not ;)

schmalex 20th December 2006 03:31 AM

2 Attachment(s)
OK, I'm reading about EM filters, etc. Here's a picture of my amp. The ground wires are white, wound together, and sealed off with tape. Not real pretty, but effective. I've been running it like this for about 20 days. It's simply BrianGT's 3886 amp, with an Avel transformer. The schematic should be widely known, but I can dig it up, if needed.

-The amp is plugged into a power strip, into the wall outlet.
-The input is an Adcom preamp
-The only source (other than the tuner in the preamp) is my ipod
-The amp's power strip shares a wall outlet with one other power strip (which powers my laptop, external monitor, subwoofer, and afformentioned preamp).

Given that my subwoofer also has a groundloop problem, I suspect it has less to do with the construction of the amp (grounding of the case and electronics) and more to do with the wall outlet and wiring of my apartment. That said, it may be most effective to solve the problem with the wiring of the amp. There isn't much room in the enclosure, as you can see from the pic.

ianpengelly 20th December 2006 07:53 AM

Hi schmalex,

I have the same problem with my amp and like the advice above some form of mains filtering / noise suppression is required. There are a few schematics about on the forum and on the web generally for these or you could buy a noise suppression IEC inlet or get a plug in filter such as those sold by Russ Andrews (The Silencer) and the likes.

I have yet to try any of the above, but I do know that I don't have this problem with the rest of my hi-fi and all it i has noise suppression, so it must work.

Hope this helps.


BrianDonegan 20th December 2006 11:27 AM

Here's a simple test. If you have your mains (AC) ground connected to the amp circuit, try disconnecting it temporarily and see if it lessens the problem.

jackinnj 20th December 2006 03:07 PM

First off, you built your amp in what appears to be a wooden cabinet -- so there's no hope for ridding EMI/RFI -- and that IPOD power supply is going to sing like a buzz-saw.

let's now imagine that you have decided to use a aluminum cabinet -- place a 200pF cap between the inverting and non-inverting input pins of the amp.

connect 100nF ceramic caps from the V+ and V- pins ofthe chip to ground -- this will decouple some of the EMI to ground.

if you can, get a Corcom EMI filter -- one that will handle 10 amps is about $12 -- Digikey carries them.

i have taken to this grounding scheme -- the green mains line is attached to the chasis at the point of entry with a 8-32 screw and solder lug, using a star lock-washer -- I run a #12 green line from this point to the ground of the filter cap

when EMI is a problem, try to cure it at the source -- the manufacture of the fridge and stove have a "Part 15" problems -- FCC rules with respect to emissions -- some of the cheap stuff sold into the US from overseas has no forethought on EMI problems.

Burnedfingers 20th December 2006 09:47 PM

Get rid of the stove and refrigerator.

Sorry, couldn't help myself.

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