Getting Rid of Transformer Hum

@rakuennow 

 

Two things, one it concerns me that you are seeing such a large drop under load. Some drop is expected. That large a drop could be indicative of a poor connection somewhere or undersized wires.

DC offset on the AC line is caused by unbalanced loading on the positive and negative going sides of the AC wave. It does not happen often, but it also does not take much to cause hum. Old 2 position dimmers (popular on range hoods), 2 position motor speed controllers (some ceiling fans) may in one switch position only conduct for 1/2 a cycle. With other electronic equipment performing poorly, the conduction on one 1/2 the cycle may be lower. Result is DC offset on the AC line.

iFi, Isotek, audiolab, ATL audio, etc. make these. There is not a lot in them. Couple of capacitors and some diodes. The diodes are to ensure the voltage on the capacitors never gets very large. If it does not have a safety certification (UL, TUV, ENEC, etc.), then get one in a metal box in case there is a failure.

I had same problem in our 120 yo house even though I have dedicated AC lines.

It's called “DC offset” and it was fixed instantly by installing an Emotiva CMX-2.
 

 

I appreciate your response. A new halogen desk light set at 1/2 on a different circuit solved my AMP5 Hum eight years later. I also noticed an annoying pulsating hum that reminds me of a lightsaber match from Star Wars once it was connected to a power source.

Magnetostriction. It’s usually another item in the home that will cause amp hum (not heard through the speakers)
Most common items are:
LED lights, Fan Speed controls, Some lamp dimmers, proportional temp controls on old range tops, coil heaters with thermostat fans, etc. None should be leaking DC back into the mains but they often do.

tone222,

Thanks ! 8 years later and your post solved my AMP5 Hum, a new  halogen desk light set at 1/2 on another circuit.

Salute ! 

I have a pair of Aragon 1Ks and one night I turned them on to hear a loud humming buzz comming from both units. I have a pair of dedicated 20 amp power lines running from the main household fusebox (one to each amp) so nothing else is on those circuits. Then I remembered my home theatre subwoofer making a similar humm/buzz when the halogen lamp in that room was set to half power - on the same cicuit as the subwoofer. So today I went across the house into the home theatre area and sure enough that same halogen light was turned on at half power, so I turned it off and the humm/buzz in my amplifiers dissappeared. Hence, even though it was across the house on a different circuit that light was still feeding DC voltage back through the main fusebox and into the dedicated lines going to my amplifiers. Hope this post helps others.

Here's a post from Roger A. Modjeski on AudioCircle.

"One thing to keep in mind about toroids. If there is any DC on your power line the transformer will audibly buzz and the magnetizing current will go up. This is because they have no air gap. EI transformers have an unintentional air gap of about .001 inches. That's all it takes to keep a transformer happy with a volt or two on the line."

This is exactly in line with my own experience: toroidals all hum/buzz to a certain extent; amps (e.g. most tube amps) that use different styles of transformer tend not to...

Sorry if that confused you. The irony is that transformers hate to have DC provided to them on the inlet but they do a great job of eliminating DC on the outlet side. Then, it usually gets rectified anyway.

That's why I didn't suggest using an isolation transformer in front of the amp. Although it would probably solve the noise in the amp by eliminating DC to it, the iso tranny would be just as likely to hum. The problem might just be relocated. And I like iso trannys.

Should also mention that the reason you don't see a lot of the Channel Islands type of thing and why the DaBlok is DIY is because capacitors aren't intended for AC mains and there is a slight chance of the caps going "poof" or "bang". No, we're not talking dynomite here but it's scary enough for manufacturers. Thus, the heavy duty case, expensive components and the cost.

Have you gone to your breaker panel yet and turned off everything except the wall outlets to the stereo? Unpugged the TV cable and any dimmers or 2 or 3-way lights? You might find the source of the DC is something that seems completely unrelated.

Tvad is right, there are other causes for noise besides DC but I'm stickin' to my story unless you prove me wrong. Maybe even after that.

The irony mentioned by Ngjockey is what confused me. I've since read plenty of articles like the one Tvad provided (btw, thank you), on magnetostriction and DC. However, the consensus seems to be that all quality Toroids and modern electric equipment should be sufficient at removing DC. The ones proposing DC as a main problem all seem to be selling something. Still, there are people as there are here, in this thread, that says an isolation transformer, or a device like the Channel Islands Audio XDC-2 solved all their problems.

So here, I'm at crossroads with my wallet since I really don't want to spend colossal amounts of money (to me) on all these devices, which in my opinion, are being marked up ridiculously.

I'm entertaining, though, one alternative option. I could try to sell my Panamax "line conditioner", and buy a used voltage regulator, which should take care of magnetostriction, and to my underestanding, DC as well. Are there any opinions on this?
i.e. Monster AVS 2000, PS Audio Power Plant...

I'll probably end up getting the CIA XDC-2 if it turns out the Monster would be insufficient...

Core saturatuation caused by DC. Period.

Question is whether it's coming from inside the house or outside.

The irony is that transformers are great at eliminating DC.

http://diyparadise.com/dablok.html

I had this problem with my Spectron Musician ii and subwoofer amplifier, and it did end up being a result of DC in the line. As far as a I know, the only company selling a solution right now is Channel Islands Audio. It is a two outlet box called the XDC-2, $299. It solved my problems completely. Call them and tell them what you have, and they can recommend the proper configuration.

I had a loud hum from what was a well designed amp, with a toroid reansformer, a Karan K180. As I understand it Toroids are prone to hum and it is mechanical, at least in part. I found an Audience AU 24 power cord cured it immediately, a bit to my suprise

An amp will hum without interconnects hooked up and speakers and power attached. Does it hum with the interconnects attached? If so, is it hum or vibration? If it is hum it may be fixable if vibration, probably not, unless the transformer has become loose. If the transformer is loose, you may be able to tighten it.

But I had a Krell amp that had a noisy transformer years ago and Krell had to send me a new amp.

Tvad, do toroidal transformers usually degrade with age, or is there anything specific that would make it go bad? I doubt a high-end amp would employ a cheap toroid to begin with. If amps/toroids do regularly go bad over time (5 years?), I would be more weary making future audiogon purchases...

I had a similar problem couple of times. First try and lift the ground anyway - in a safe manner of course. I would suspect though that you have some bad DC on the line - try plugging the amp into a different circuit in your home. You can also try the noisehound from Blue Circle or one of the PS Audio devices to take out the DC.