electrical noise affects amp - solution?

[firedog]

Hi-

 

I've been getting an intermittent hum/vibration from my amp. Not heard through the speakers, but heard coming from the amp. Consulted with the manufacturer and he suggested it is caused by lack of current to the amp and/or noise from lights or appliances such as the fridge. My observations would seem to back up the idea that the fridge and other devices are producing noise that goes to the amp.

 

question: is there anything I can do about this? I don't want to limit current to the amp or make it sound flat. Would adding an independent circuit just for the stereo system or amp help?

 

Thanks

[Raym87]

If the noise / hum is heard all the time then your diagnosis is likely correct. However, if the hum is internittent then the likely cause is DC on the mains.

If its the former than a decent mains conditioner should help to clear it up. If the latter then there are DC blockers available. A Google search will provide more info. Just to get you started....... POWER DC X-TERMINATOR - DC offset hum transformer noise brom

Look at their product sheet. It helps with diagnosis.

Adding a dedicated circuit will help reduce, not eliminate pops and clicks from fridges etc. it is usually considered a good move to do so. It wont make any difference if the problem is DC though.

It may be worth getting you mains checked as the idea that you arent able to supply enough current to your amp is a concern.

[firedog]

After reading the material, it seems that the problem is DC offset. I came across this (avahifi - AVA Humdinger) and it seems like this is just what I need.

[Raym87]

Another option would be to consider a balanced transformer. It will help with common mode noise rejection and would block any DC on the mains. As you may know, a transformer will not pass DC.

This would probably be more expensive but maybe worth a look.

[4est]

Then wouldn't that transformer hum instead?

 

Mains DC and Transformers

Another option would be to consider a balanced transformer. It will help with common mode noise rejection and would block any DC on the mains. As you may know, a transformer will not pass DC.

This would probably be more expensive but maybe worth a look.

[Raym87]

Then wouldn't that transformer hum instead?

 

Mains DC and Transformers

 

Yes. But theres the option of putting it down the line so its out of the way.

[Speedskater]

The real solution is to track down the offending appliance if you can. Sometimes electric water heaters, room heaters or cooking unit generate this trash. Try other circuits, also look to nearby neighbors, does it happen at a certain time of day or weather conditions. But if you have nearby commercial building you may be out of luck.

[speavler]

I used to get transformer buzz from my krell amps in my old house. used the ps audio humbuster iii. worked like a charm.

[flatmap]

The real solution is to track down the offending appliance if you can. Sometimes electric water heaters, room heaters or cooking unit generate this trash. Try other circuits, also look to nearby neighbors, does it happen at a certain time of day or weather conditions. But if you have nearby commercial building you may be out of luck.

+1

When the family's out of the house (so they won't think you've gone crazy) go ahead and flip off the circuit breakers to everything else in the house and then unplug everything else on the circuit your amp is using. This rules out interference from other appliances... or that new display lighting in the trophy case upstairs. If that eliminates the hum then you can add stuff back in.

 

You haven't, perchance, just installed a new dimmer switch somewhere have you? I've had trouble with those in the past.

[gmgraves]

Hi-

 

I've been getting an intermittent hum/vibration from my amp. Not heard through the speakers, but heard coming from the amp. Consulted with the manufacturer and he suggested it is caused by lack of current to the amp and/or noise from lights or appliances such as the fridge. My observations would seem to back up the idea that the fridge and other devices are producing noise that goes to the amp.

 

question: is there anything I can do about this? I don't want to limit current to the amp or make it sound flat. Would adding an independent circuit just for the stereo system or amp help?

 

Thanks

 

I Don't know anything about your particular amp, of course, but I think the manufacturer misunderstood your problem.

In my long experience, that kind of noise - coming from the component, itself, rather than from the speakers - is indicative of a faulty or loose power transformer, not by any "lack of current to the amp" or noise from a 'fridge, or lights or other appliances. I would think that those faults would cause hum and noise in the speakers, not from the physical assembly of the amp itself. Remember that the current load of the amp itself might cause the severity of the problem to change with whatever the amp is playing, or with the line voltage of your household mains. Yes, other appliances could affect that voltage, but a properly coupled (to itself and to the chassis) power transformer won't sing if it's tight, even if the load or voltage do vary.

 

My last amp (before my current one) was a Krell and a good sounding piece it was, however, it hummed and buzzed like a beehive. I finally got tired of listening to it and opened it up. Sure enough, the torroidial power transformer was loose in the bottom of the chassis. Tightening the screw holding it down, fixed the problem. Other amp designs might use laminated transformers. Laminated power transformers can have another problem other than just being loose from their chassis moorings. The laminations that make up the transformer's core are comprised of alternating sheets of soft iron. some are shaped like an "E" and the others, like an "I". The result is a laminated pack shaped like a squared-off figure "8", where the windings are wrapped around the center bar of the "8". The laminations need to be tightly coupled together. If the pack becomes loose the laminations will hum and buzz at the line frequency and at harmonics of that frequency. Sometimes the laminations are held together with srews and nuts, and in that case, one can just tighten them with some hand tools and pack the laminations back together stopping the humming and vibrations. Unfortunately, many power transformers, especially large, heavy ones used in power amplifiers are often "potted", that is to say, they are housed within a metal enclosure (usually for cosmetic reasons) and the area between the transformer itself and the housing is filled with a solid, tar-like substance that goes in as a liquid and then sets-up. This usually keeps the transformers quiet, because it's difficult for the laminations to move when surrounded by a solid matrix of material with damping properties. As unlikely as it seems, these too can develop a vibration, and when that happens, I'm afraid that the only fix is to replace the entire transformer.

 

Check your power transformer first before looking for the reasons the manufacturer outlined (again, I think they misunderstood what you were saying). If you are having trouble locating the source of the buzzing within the amplifier chassis, try this old car mechanic's trick for finding the source of unwanted noises from an engine: Take a screwdriver and hold the handle-end tight to your ear. Place the screwdriver tip against various components in the amp (careful now, there could be high voltage!), then against the power transformer. If the transformer is the source of the noise, the noise will get much louder through the screwdriver. If it is the transformer, you might be lucky and be able to tighten it. I hope this helps.

[firedog]

George and flatmap-

I'm suspecting from what I've heard and read that the problem is DC related. The descriptions of that seem to match what I'm hearing.

 

However, your suggestions for tracking down the source of the hum/vibration are good ones and I will try them to make sure I'm not barking up the wrong tree. I am, by the way, pretty sure the transformer is screwed in tightly, but I will check again.

[firedog]

Okay, so I did this. Unplugged everything and turned off all the circuit breakers except the one to the amp. The circuit breaker to the amp also controls the lighting in the room with the amp.

 

One by one engaged each circuit breaker. No noise.

 

Starting with the lights in the room with the lamp, gradually turned everything back on. No noise. The amp and all the

other appliances have now been on for about 15 minutes and everything is quiet.

 

I’m assuming the noise will come back at some point and then I will try the screwdriver test to what inside the amp is vibrating.

 

But for now, as the noise seems to be intermittent, I’m thinking the idea of intermittent DC pollution in the line must have something to do with it.

 

Comments?

 

You guys have been VERY helpful. Thanks

 

+1

When the family's out of the house (so they won't think you've gone crazy) go ahead and flip off the circuit breakers to everything else in the house and then unplug everything else on the circuit your amp is using. This rules out interference from other appliances... or that new display lighting in the trophy case upstairs. If that eliminates the hum then you can add stuff back in.

 

You haven't, perchance, just installed a new dimmer switch somewhere have you? I've had trouble with those in the past.

[gmgraves]

George and flatmap-

I'm suspecting from what I've heard and read that the problem is DC related. The descriptions of that seem to match what I'm hearing.

 

However, your suggestions for tracking down the source of the hum/vibration are good ones and I will try them to make sure I'm not barking up the wrong tree. I am, by the way, pretty sure the transformer is screwed in tightly, but I will check again.

 

 

OK, obviously, I have no real idea what you might be hearing, except what you have said in your earlier post. But I don't really see how buzzes and hums can be DC related in a well-designed power amplifier. But I suspect you have a better handle on that than I have. You're there, I'm not. You're talking to the manufacturer, I'm not. Good luck.

[firedog]

OK, obviously, I have no real idea what you might be hearing, except what you have said in your earlier post. But I don't really see how buzzes and hums can be DC related in a well-designed power amplifier. But I suspect you have a better handle on that than I have. You're there, I'm not. You're talking to the manufacturer, I'm not. Good luck.

 

low-level DC voltage sitting on your AC power line that causes the power transformer to hum or buzz.

"This type of mechanical transformer hum may be caused if other devices on your power line, or devices on nearby power lines, use AC power asymmetrically. This quite common low level DC tends to make toroid power transformers hum and overload. The effect is often seen in products with toroid transformers, but it’s not limited to just toroids; thus, the non-toroid transformers can also hum depending on the level of DC voltage on the AC line."

 

{DC on the mains)

causes cores in audio-power transformers to saturate, causing them to hum...

 

not arguing, just quoting what I've read.

 

About an hour after my previous post, the hum started at a very low level again. At that level it is almost not noticeable and I'm going to wait until it gets stronger, and then try to see exactly where in the amp the vibration seems to be coming from. I have checked the transformer and it is not loose, so that's not the problem.

 

Thanks again, George.

[gmgraves]

Okay, so I did this. Unplugged everything and turned off all the circuit breakers except the one to the amp. The circuit breaker to the amp also controls the lighting in the room with the amp.

 

One by one engaged each circuit breaker. No noise.

 

Starting with the lights in the room with the lamp, gradually turned everything back on. No noise. The amp and all the

other appliances have now been on for about 15 minutes and everything is quiet.

 

I’m assuming the noise will come back at some point and then I will try the screwdriver test to what inside the amp is vibrating.

 

But for now, as the noise seems to be intermittent, I’m thinking the idea of intermittent DC pollution in the line must have something to do with it.

 

Comments?

 

You guys have been VERY helpful. Thanks

 

In the old days, dimmer switches for incandescent lamps, which worked by chopping the AC line voltage to the lights and varying the lamps' duty cycle to alter their brightness could get into amplifiers and cause buzzes as could fluorescent lamp starters and ballasts. But modern dimmers and fluorescent lamps don't work like that any more, and shouldn't cause that problem.

 

See if you can borrow an oscilloscope from some electronics hobbyist friend and put it across your mains near where the amp is plugged-in. If you have that kind of noise on your line, it should show up on the o'scope. My whole house has fluorescent bulbs that have replaced incandescent types and I have heard none of the noise you speak of. I also have a (physically) very noisy fridge as well as a big window AC unit as well as various computers. Today's electrical appliance manufacturers are very conscious of the possibility that their products could produce interference that would get into TVs, radios, and stereo systems and they try to design it out. And , of course, parts can fail, and therefore "gang aglee" the best laid plans of mice and men.

[speavler]

I have newly installed dimmers that create noise on my line. Hear it through my subwoofer. And this with a dedicated line for my AV system. Have also had issues with CFL's with no dimmer.

 

I went through this transformer buzz thing years ago when I was living in an old house that still have knob and tube wiring in half the house. Had a dedicated line put it, but still didn't help. It wasn't that loud, but any sort of hum or buzz in my system drives me insane. There were some very helpful threads on audiogon that lead me to the ps audio product. The humbuster worked for me. Completely eliminated the buzz. My new house has no such issue and the Krell amps are quite as can be without the humbuster.

[sandyk]

See if you can borrow an oscilloscope from some electronics hobbyist friend and put it across your mains near where the amp is plugged-in

 

George

That is very dangerous advice. A CRO should never be connected directly across the mains without special isolation measures taken.(Current clamps, Isolation Transformers etc.)

Regards

Alex

[gmgraves]

George

That is very dangerous advice. A CRO should never be connected directly across the mains without special isolation measures taken.(Current clamps, Isolation Transformers etc.)

Regards

Alex

 

 

Hmmmm I've been doing it for decades, never had a problem. Obviously you don't want to touch bare leads or connectors while doing this. That's about the only danger that I can think of.

[sandyk]

George

There are very clear published warnings in several publications on this subject, as well as published projects.

You might get away with it in the USA, but 230V AC is a different ball game.

 

Regards

Alex

[dc2bluelight]

Hmmmm I've been doing it for decades, never had a problem. Obviously you don't want to touch bare leads or connectors while doing this. That's about the only danger that I can think of.

 

Scope probes include a ground connection. Many scopes have that connection tied to their chassis. Clipping that ground on the wrong wire will blow a breaker/fuse at least, with the added entertainment of some fireworks and a damaged 'gator clip, with personal injury as an unpredictable added bonus.

 

I'd vote for isolation too, unless you're trying to look for a DC component. AC waveform asymmetry and DC are two different things, asymmetry will mostly get through a transformer, DC won't. So in that case, take an old motor starting cap and a series resistor around 15K-20K, but them across the AC line, measure the DC across the cap. Only a few DVMs will handle full AC line voltage on the DC function, so this little circuit filters most of it out.

[sandyk]

Ever tried looking at the DC side of an old transformerless colour TV with a typical scope connected to mains earth ? (embarrassed smile)

[gmgraves]

George

There are very clear published warnings in several publications on this subject, as well as published projects.

You might get away with it in the USA, but 230V AC is a different ball game.

 

Regards

Alex

 

Ah, yes. I'd forgotten that you hail from 50 Hz, 230V territory

 

It's not really a problem here. In fact, my GP Oscilloscope for many years was a Dick Smith model from OZ, and I have had that across my mains line many times over the years.

[gmgraves]

Scope probes include a ground connection. Many scopes have that connection tied to their chassis. Clipping that ground on the wrong wire will blow a breaker/fuse at least, with the added entertainment of some fireworks and a damaged 'gator clip, with personal injury as an unpredictable added bonus.

 

Yes it can. Good scopes have the signal ground separate from the chassis ground. I started life with an Eico 'scope kit my dad built when I was a kid. Even it, as cheap as it was, had separate signal and chassis grounds. My old Australian Dick Smith 'Scope likewise has isolated grounds and needless to say my Tektronix 465 has that feature to (although I use a 10:1 probe with that one).

 

I'd vote for isolation too, unless you're trying to look for a DC component. AC waveform asymmetry and DC are two different things, asymmetry will mostly get through a transformer, DC won't. So in that case, take an old motor starting cap and a series resistor around 15K-20K, but them across the AC line, measure the DC across the cap. Only a few DVMs will handle full AC line voltage on the DC function, so this little circuit filters most of it out.

 

Yeah, that will work fine if one doesn't happen to have a attenuating probe handy.

 

Guys, I didn't mean to start a donnybrook here, I merely meant to point out that the best way to find what's causing our OP's noise is for him to look at the waveforms involved and see whether the problem comes from interference on the mains, a low-voltage situation, or is a function of something amiss on the amp itself.

[One and a half]

There are scopes that can measure up to 600V directly with the isolation built into the scope. Amec, Tektonix, Agilent and Fluke produce these models.

[sandyk]

Ah, yes. I'd forgotten that you hail from 50 Hz, 230V territory

 

It's not really a problem here. In fact, my GP Oscilloscope for many years was a Dick Smith model from OZ, and I have had that across my mains line many times over the years.

 

Which CRO do you think I was using when I stupidly blew up rectifier diodes in that old Sharp transformerless TV?

Some DSE CROs may have had this feature, but mine didn't .