I live in a small apartment, with what is apparently subpar wiring. I recently completed my chipamp.com 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.
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.
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.
-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.
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Hi schmalex,
I have the same problem with my chipamp.com 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.
Ian
I have the same problem with my chipamp.com 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.
Ian
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.
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.
I would want to test the wall outlet for a possiable mis-wired outlet.
Using a device like this:
http://tinyurl.com/yyduxn
just to be sure everything is A-OK. Also be sure to check the Fridge and other outlets too.
johnm
Using a device like this:
http://tinyurl.com/yyduxn
just to be sure everything is A-OK. Also be sure to check the Fridge and other outlets too.
johnm
For what it's worth:
I built my first gainclone with amp and power supply in the same enclosure. I had the same problems you had and more. I tried everything that the very helpful forum members suggested.
Then, just for the heck of it, I rebuilt it in two separate enclosures. All the problems disappeared. I've built 3 more since, in separate enclosures, and have never had a problem with hum or EMI.
Again, for what it's worth.
I built my first gainclone with amp and power supply in the same enclosure. I had the same problems you had and more. I tried everything that the very helpful forum members suggested.
Then, just for the heck of it, I rebuilt it in two separate enclosures. All the problems disappeared. I've built 3 more since, in separate enclosures, and have never had a problem with hum or EMI.
Again, for what it's worth.
burnedfingers said:
Along the lines of wacky (or not so wacky) solutions...here's AndrewT's favorite
Take off the mains AC ground and do not connect it to chassis...isolate it with a piece of electrical tape. Then go out and buy yourself a little GFCI plug-in device for safety like these little Leviton items.
http://www.twacomm.com/assets/pdf/19157.pdf
VOILA! No more hum...guaranteed. Do the test for yourself. Run the amp with along with the other noisy appliances in your swanky place and disconnect the mains AC ground for a second.
The EMI filters mentioned thus far should help... I use them on EVERYTHING I build.
Also, consider putting a couple of TVS, Transient Voltage Suppressers, across the outputs of your PSU. These are really nothing big zener diodes. They will clamp transients that can ride through PSU when the app's switch.
Also, consider putting a couple of TVS, Transient Voltage Suppressers, across the outputs of your PSU. These are really nothing big zener diodes. They will clamp transients that can ride through PSU when the app's switch.
An interesting side benefit to floating the signal and DC power grounds off the chassis is that all the concerns about using an LM3875T (nekkid LM3875) versus the plastic package LM3875TF and accidentally grounding the exposed chip tab on a chassis part (thereby ruining it if the chassis is grounded to the DC power ground) go out the window. N'cest pas?
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