Getting Rid of Transformer Hum

Sounds like the amp needs a new/better toroid. I seriously doubt if any power conditioner/regenerator is going to solve the problem.

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.

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...

05-02-08: Rakuennow
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.

Like most things, there are toroids that are better (quieter) than others. The cost of an amp may have no relation to the quality of toroid installed.

I have not heard of toroids degrading with age. Voltage dipping 10% or more from a toroid's rated voltage can cause hum.

Why not have a technician check it out? Perhaps tightening the screw, or adding damping material would solve the problem. A new toroid would certainly be less expensive than a replacement amp.

Channel Islands Audio makes a power conditioner designed to eliminate or reduce transformer hum. You could give it a try.

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.

The way I read it the Amp has three toroid transformers.

Good chance the hum/buzz is being caused from DC voltage on the AC mains.

Nelson Pass.
If you are experiencing mechanical hum from your
transformer, it is often caused by the presence of
DC on the line. Usually this comes from some appliance
using current asymmetrically, such as a lamp dimmer.

The hum comes usually from toroidal transformers, which
saturate easily with DC, and when they recover, they
draw an extra pulse of current, causing the noise.

You can put a pair of back-to-back electrolytics in series
with the AC power line to block this, and it works fine.
Makes sure the current rating of the electrolytics is
high enough, and the they are joined at a like polarity,
such as + to +.

>>

Eva.
I've done some measurements that show what's really hapening when you connect a transformer to mains

Using a lowpass filter [100k + 47uF] I have measured about 50mV average over time of DC on my mains supply

I also have an old electric heater that in half-power mode uses a diode in series with the heat element to pass only half of the mains waveform. When I plug this heater in half-power mode I get an additional 1V of offset on mains supply

To test the need and the efficiency of DC filtering, I've done some measuremens of the current through the primary of a 750VA toroidal transformer

This oscillogram shows what happens when I connect the transformer to mains and let it deal with the 50mV DC offset

Blue trace is mains waveform at 100V/div [230V AC], it looks more like a clipped triangle wave instead a sine wave due to the line inductance limiting the slew rate and all the rectifiying applications consuming all the current only during the peaks [30% of total time]

Red trace is the current through the primary at 200mA/div. Transformer saturation towards the negative side is evident, reaching 350mA peak of leakage current. The transformer buzzs slightly due to the saturation

The noise present in the current waveform is common mode and was suppressed in further measurements adding a common mode filter between mains and measurement point

The second oscillogram shows what happens when I plug the electric heater in half-power mode

Red trace this time is in 2A/div so the leakage peak current exceeds 6A. The transformer is heavily saturated towards the upper side and buzzs loudly.

The third oscillogram shows what happened when I placed a DC filter consisting of two 1000uF 16V and some diodes in series with the primary

This time, red trace is 20mA/div and shows the small leakage current due to both the magnetizing inductance and the parasitistic capacitance between adjacent turns. The transformer is no longer saturated and performs silently

the fourth oscillogram shows the induced voltage in a loop of wire of 10cm diameter placed vertically, paralell and 1cm away from the transformer [placed horizontally] obtained when the transformer was saturating with more than 6A peak [with the electric heater plugged]

The red trace is 2mV div and shows the induced voltage in the loop of wire

That measurement demonstrates that when a 50-60Hz transformer is saturating, it produces electro-magnetic-interferences that induce noise voltages on everything in the nearhood

Actually, I think that +-5mV of low frequencies induced in a loop of wire of 10cm diameter near the transformer is a serious thing since this EMI is at audio frequencies, it's not RF so it's 100% audible and it may be happening in all your transformers

In the other hand, all the tests were performed with open secondaries but if we add load so that primary current has peaks of 6A, then the EMI radiated would be the same or higher

With load, the EMI is produced due to flux in the leakage inductance, resonances due to parasitistic inter-turn capacitance, RF ringing due to diode turn-off characteristics and the fact that the peak current through the transformer is 3 times or more the average DC current after rectification

In conclusion : Rectifiying the output of 50-60Hz transformers produces EMI as any SMPS does and this phenomena gets aggravated when the transformer is saturating due to direct connection to mains without a DC filter

50-60Hz transformers are nothing but big, bulky and crappy antennas.
Eva

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

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.

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

Read this article. It's written so a layman can understand it.

Essentially, there are two causes of transformer hum: magnetostriction and DC. Magnetostriction is what I referred to above in which the voltage on the AC line drops more than 10% (or increases more than 10%) from the toroid's voltage rating.

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...

The CIA XDC-2 can be tried and returned for a refund (less restocking fee) if it doesn't work. That's where I'd start.

If you own other components with toroids, and if they don't hum, then you know the problem is confined to the one component.

If the CIA device doesn't work, then I'd consider buying a different amp rather than throwing money at a problem that's likely inherent with the component itself.

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.

Rakuennow
However, the consensus seems to be that all quality Toroids and modern electric equipment should be sufficient at removing DC.

Ain't gonna happen..... It's the nature of the beast. DC voltage interring the primary winding of a toroid transformer will cause mechanical noise.
That is, if there is DC voltage on the mains.
==========

The ones proposing DC as a main problem all seem to be selling something..

Nelson Pass nor Eva Manley are trying to sell devices to filter out DC voltage.
For a few bucks you can build a DC blocking filter as Pass and Manley talked about in their posts on DIY
==================

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 suggest you first check the back of the Amp and see what the manufacture voltage rating is. Is it 120V or 115V?
Even if it is 120V 10% under would put the voltage at 108V.
Then there is your meter...... How accurate is your meter?

>>>>>>>>>>
.

Ngjockey
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.

Ngjockey, if it is a concern a fuse could always be placed ahead of the filter circuit.
.

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...

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.

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 !