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Old 15th January 2012, 11:50 AM   #1
seebert is offline seebert  United States
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Default Either all my amps have problems or .... ??

Hi all. Going slowly insane. I thought I had a fault with a Threshold amp - a buzzing/rattling power transformer - quite loud. Changed it out to a different Threshold - quiet for a moment and then the transformer noise just like the first amp. Changed it out again for a Muse160 and ... quiet at first then the buzz/rattle.

BUT it is not constant I've found. Sometimes the noise goes away, sometimes I switch on an there's no transformer noise for quite a time but the time varies from minutes to an hour or so. It just comes and goes.

I don't know if this is in any way related (I can't see how it could be) but all of these previously heat stable amps are heating up on one side more than the other by a definite amount that's easily felt by hand; not red hot but way hotter than the other channel.

There is no (hum/buzz etc) noise through the speakers. No distortion.

I have both an anti-surge strip and a Panamax 4300 - amp noise as above. I've tried plugging into the mains directly and it makes zero difference - the transformer noise (and heat) problems stay the same.

Live in a tiny town (500 residents) with medieval facilities and get brown outs pretty often but checked the line voltage and it's 122VAC with and without the noise. There are be some big 'farm factory grain do-somethings'
a block away but nothing much else. The local emergency radio controller lives and transmits from next door and have had problems with RF in the past but that doesn't seem to be the issue here I don't think.

ANY ideas please - I'm just about ready to go off bang.

Thanks, Mike.
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Old 15th January 2012, 11:54 AM   #2
dhaen is offline dhaen  Europe
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Possibly a small DC component on mains. There are threads here with countermeasures.
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Old 15th January 2012, 12:04 PM   #3
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Possibly a small DC component on mains. There are threads here with countermeasures.
That can explain everything except the hot channel...

I would believe there are some HF oscillation in one channel in the chain prior to the poweramp.
What you hear are the transformer delivering higher current than normal standby caused by the HF oscillation.

Normally transformers will make noises when you play loud due to increased currents, but normally this in masked by the loud audio level.
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Old 15th January 2012, 12:07 PM   #4
Bonsai is offline Bonsai  Taiwan
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Yes, sounds like DC on the mains. As a first suggestions, turn off ALL your appliances in your house. If the problem goes away, your problem is on one of your appliances. Solution is simple: turn it off when you use your system. However, if after turning all your appliances off the problem is still there, then your problem is coming in on your mains feed. That's more to solve.

I had this problem on my Ovation amp when I was in Japan - quite scary when a 2KVA transformer starts singing and buzzing. I found out is only happened when the dish washer (an old Westinghouse model) ran. Looks like they were feeding some part of the the circuitry with half wave rectifier and that is what was causing the problem.

Anyway, hope you solve your problem!
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Old 15th January 2012, 12:09 PM   #5
Bonsai is offline Bonsai  Taiwan
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RayCtech, that's also a possibility! But, would it happen on all the amplifers?

Seebert, try turning yout mains plug thru 180 degrees and see if the other channel gets hot. Just a thought.
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Old 15th January 2012, 12:13 PM   #6
system7 is offline system7  United Kingdom
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Don't know about DC on the mains. Guess that is possible. I was thinking some sort of oscillation on one channel too. You might think about whether your speakers/cables are presenting an awkward load at HF causing oscillation in what looks like a simple Nelson Pass (low feedback?) design. You can do something about high frequency speaker loading with Zobel networks and like.
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Old 15th January 2012, 12:20 PM   #7
Bonsai is offline Bonsai  Taiwan
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DC on the mains is a very common problem - and especially an issue with large torroids (they have low DC resistance primary's). Take a look at Rod Elliot's side for details below

Mains DC and Transformers

Rod's site BTW is a gold mine of information. Highly recommended.
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Old 15th January 2012, 12:21 PM   #8
seebert is offline seebert  United States
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Thanks to all for the information and helpful comments.

What I don't understand is that I have changed absolutely nothing in this house and all was okay previously right up until today.

I did go around the entire house (a small cottage really) and make sure nothing was amiss or even switched on!! No difference with everything including the refrigerator and entire heating system switched off. Also I am at a loss to understand why the noise is on ... and then gone ... and back again ... and so on.

If it's DC on the mains it should be fairly constant yes? Or at least not off-on as it is right now. And the odd 'one channel' heating thing - I've just got no idea why this would suddenly develop on all 3 of the amps I've switched out. Unbelievable coincidence or ???

Haven't moved the 'guts' of the speaker cables - just the 'ends' to hook up the amps - and again that's why I'm so confounded - if there was no HF oscillation before today what on earth could I have changed out that I've missed or forgotten about?

Mike.

Last edited by seebert; 15th January 2012 at 12:26 PM.
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Old 15th January 2012, 12:25 PM   #9
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RayCtech, that's also a possibility! But, would it happen on all the amplifers?

Seebert, try turning yout mains plug thru 180 degrees and see if the other channel gets hot. Just a thought.
DC on the mains should not be able to cause only one channel to get hot...
And the hotter channel was replicated to the other amps.

Normally DC on the mains will affect some amps more then others.
Thus both transformer noises and a hotter channel also on a totally different brand of the amp indicates something more than DC on the mains.

Valve / tube preamps can cause this.
Either a DC leakage in the output capacitor or a valve / tube that are defective and oscillates.
Both cases can give a varying DC offset to the poweramp.

I would have measured the DC offset on the outputs of the poweramp and preamp when the transformers are making noises.

The interconnect cable between the preamp and poweramp can be disconnected to check if the transformer noise stops..
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Old 15th January 2012, 12:27 PM   #10
Bonsai is offline Bonsai  Taiwan
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No, DC on the mains depends on whether or not the quipment causing the problem is turned on or not - so it will be an on-off problem.

Can you tell us what speakers you are using and something about your cables?

If you disconnect your speakers, do you still get this problem?
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