[yeldarb]

I've got a plate amp in one sub that hums or buzzes.  This is not hum expressed at the driver, this is hum I can hear when the amp is off but still plugged in.  Pretty sure it is the transformer vibrating with ac.  Anybody got any suggestions about lessening it or stopping it altogether?  I can't hear it, normally, when listening to music, but it has to "muddy" the bass. 

[avahifi]

Do you have two identical subwoofer/plate amp combinations?

If so swap the AC power to both of them and see if the buzz follows the AC power line.  If so you have a dirty AC power line that the power transformer does not like. This can happen from low level DC on the line, coming from other devices on that circuit that use diodes to vary their input power.

If it does not swap, then the issue is likely a loose plate in the transformer of the noisy plate amp, or possibly loose mounting hardware for that transformer.  If tightening (or slightly loosing) the plate amp mounting hardward does not fix it, then the only cure is a replacement power transformer (or plate amp - -  depending upon its warranty status).

Regards,

Frank Van Alstine

[roscoeiii]

I had some nasty transformer hum on my amp's toroid at my old apt, which was due to DC on the AC line. The two commercially available items that can deal with that are the PS Audio Humbuster, and a similar CI Audio device. Both are around the same price and come with a return policy, so you can purchase it, and if it does not fix the problem you can return it with no problem.

IIRC, the CI Audio version has a couple options that allow you to get a device that is most suited to the gear that has the hum.

Hope this helps.

Roscoe

[Rocket]

Hi,

I am at my wits end with my Ampzilla monoblocks and I have had persistent hum/buzzing from one of the amps.  I even bought a ps audio humbuster III and whilst it did reduce the hum the buzzing is still ever present.  I spent a lot of money on this amplifier and I'm not getting any help from the manufacturer.

Good luck with fixing the hum/buzz.

Regards

Rod

[Speedskater]

Does the Ampzilla (or any other amplifier) buss or hum with:

1] Only the AC power cord connected (mechanical buzz)?
2] AC power cord and speaker cable connected?
3] As above with a battery powered portable music source?
4] How about on a different AC power circuit, room and/or building.
5] Does it always hum or buss (day/night and summer/winter)?

Each problem has a different solution.

[raindance]

Two types of possible noise here:

(1) On the sub issue, it is mechanical vibration. The transformer probably needs tightening or damping using some sort of rubber, or it is a crappy transformer and buzzes internally. I don't buy the "DC on the AC" theory.

(2) On the Ampzilla issue, you don't say if the noise is through the speakers or mechanical noise at the amp. This would be helpful.

[roscoeiii]

Raindance, I am curoius why you don't buy the dc on the line theory. It was certainly the case in my old apt.

[Speedskater]

Raindance is not the only one who doesn't buy it!
I have never seen a serious paper on audio and AC power EMI/RFI even mention the subject.
Never read an explanation on how true DC would get on the AC power line (save for obsolete heating elements).

[roscoeiii]

Well, I hardly have a technical background. But when I inserted a Humbuster, which IIRC is only designed to take DC off the line, my toroid hum immediately disappeared. PS Audio and CI Audio also freely admit that toroid hum may be the result of something else. Thus the generous return policy. You will know immediately when their devices are plugged in if that is the problem or not.

Moved into a new apt, plugged in my amp with no Humbuster, no toroid hum. Sold the Humbuster. But when I had the nasty AC in my old apt it was a godsend.

And to be very clear, this is for hum that comes from the chassis, not through the speakers.

If you need an explanation, give CI Audio or PS Audio a ring. I believe this has been discussed in some diyaudio threads as well.

And ultimately what is more important, an explanation or a solution to your audio problem. The Humbuster solved my problem. Before Humbuster, a hum I could hear from my seat. After Humbuster, silence. Problem solved. And thank goodness PS Audio and CI Audio devoted some resources to a problem that it seems not many audiophiles have (only those of us lucky enough to live in an area with exceptionally poor AC power).

[Wayner]

Some home appliances, that use questionable power supplies can put DC in the lines. It is well documented that toroidal transformers are prone to internal winding noise when a DC component is present. This isn't a theory, it's well known.

Iron core transformers that hum usually suffer from plate separation somewhere in the structure and the magnetic fields generated by the transformer itself are strong enough to make the transformer buzz, the metal plates actually rattle .

Remember as a kid, hanging around the street light at night, listening to the transformer buzz of the cheap HID ballasts.

Wayner

[Speedskater]

What home appliances operate 24/7 all year?
No one reports this buzz suddenly coming and going.
I have 3 excellent papers on my desk about AC power and audio systems. About 140 pages in all, yet not  one word about DC on AC power lines.

[Speedskater]

Now in building that have 3 phase power (or even near 3 phase power) deriving single phase from the 3 phase can be plagued with problems!  But the problems are not DC.

[roscoeiii]

Maybe ci audio and ps audio can refer you to the relevant literature

[yeldarb]

Well, I tried different circuit last evening, still hum / buzz.  Tried floating the ground to no effect.  So, I took the amp out of the sub and out of its housing (cheap plastic tub).  The tranny is the usual sheet metal and plastic bell cased crap.  There were rubber insulators under the mounting tabs but the trans was screwed down tight.  So, I loosened the lower two mounting screws a bit, wrapped a band of self annealing rubber tape (stretchy stuff used for plumbing and electric work)around the trans, and crammed a bit of same under the cheap sheet metal part of the trans case.  Put the housing back on and put some rubber tape and duct tape on the "tub" to damp it a little.  Put it all back together and, cross fingers, it seems to have helped.  Thanks for the hints, folks. 

As far as DC in the line goes, there is a small machine shop about 1/2 mile away.  I once tried a switching power supply type sub, as well as power amps with switching power supplies, on this circuit.  So much crap came through those "switchers" that my preamp was getting the backwash.  So, I can believe that DC or 3 phase could have an effect.  And I had to pay to ship the unusable stuff back.  At least the transformer blocks out some of the trash.

[Rocket]

Hi,

The buzzing is definitely coming from the amplifier and not thru the speakers.  I disconnected the ic and speaker cables and this does not fix the problem. 

The buzzing does not happen immediately but does take a few minutes to warm up I guess.  Perhaps dampening might help?

Regards  Rod

[Speedskater]

Maybe ci audio and ps audio can refer you to the relevant literature

I did find 3 good discussions on the subject:

http://sound.westhost.com/articles/xfmr-dc.htm
http://www.diyaudio.com/forums/solid-state/2080-dc-filter.html
http://www.diyaudio.com/forums/solid-state/161428-variations-dc-main-filter-against-buzzing-toroid-transformers-what-right.html

Consensus was that these filters sometimes help.
However there was no agreement on what the actual problem is!
Or what the correct circuit is!

[Rocket]

Hi guys,

I received amessage from the manufacturer that it may be a bad core.  I  have to remove the tranny and send it back to the US.  After a year of dealing with this it would be great to fix the problem.

Regards Rod

[Wayner]

What home appliances operate 24/7 all year?
No one reports this buzz suddenly coming and going.
I have 3 excellent papers on my desk about AC power and audio systems. About 140 pages in all, yet not  one word about DC on AC power lines.

Refrigerators, stoves, clocks, microwave ovens, garage door openers, water softeners, TVs just to name a few. Apparently, your excellent paper didn't tell you that these appliances are "on" all the time. 24/7/365.

Even shitty designed hifi equipment can put crap into the electrical system. I think you need to go find a new 140 page paper that is even more excellent.

Happy Thanksgiving.

Wayner

[Speedskater]

Wayner, did you read my post #15?

My home has most of the above appliances and save for the clocks, none of the others operate continuously.
Yes, the supplies generate harmonic distortion on the power line but not true DC.

[Wayner]

Something as simple as a TV is on all the time, even when you think it  is off. It is powered to receive a signal from the remote control. Same  with garage door openers, and a host of other products. Those devices  are capable of putting garbage into the line, especially poorly designed  power supplies.
 
 How do I know this stuff can cause noise? I had a cheap Magnavox TV (now  in the garbage) that was doing that very thing. I discovered it by  accident when I had it unplug, that a certain noise went away.
 
 This TV also gave off RFI and interfered with AM radio.
 
 This is why I suggest that you have not explored all of your noise generating options.
 
 Wayner