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Old 24th September 2004, 04:00 PM   #1
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Unhappy Oscillating transformer buzz problem, please help!

Hi everyone I was hoping someone could let me know if they have experience with this kind of thing.

I own a Chiro Kinergetics C-500 5 Channel Amplifier. Sounds great except...

Hereís the problem. I have been getting a buzzing in the transformer over the past couple of years. The volume of the buzz raises and lowers over a couple of minutes. It doesnít always do it either. Sometimes it will go a week without a problem and them sometimes it will happen for 2 months straight. I talked to a Plitron Engineer that doesnít think itís a transformer problem. He mentioned it would probably be constant in volume and duration if it was. He pointed to the power supply and maybe the caps especially. I opened it up and saw 2 large Philips 20000uF power filter caps after the transformer on the output stages and then saw 4 1000uF Nichicon caps before the transformer near the switch relay. I wonder if it could be one of those? I also wondered why there is another transformer on the switch. It unfortunately is a little noisy also, but nowhere near as bad as the main toroid. Man, should I just toss this thing?

I know that AC noise and dirty power can cause this kind of buzz but I have moved 3 times since this started and it is always present. I have tried switching outlets and even a Monster Power conditioner and it didnít seem to help.

Also, the sound still seems fine on the outputs (except for a faint buzz in my center channel) and doesn't get worse or better as the buzz increases or decreases. This leads me to believe the problem is before the output stages. Would this make sense?

Any advice on what this could be or even schematics would certainly be appreciated. Thanks for your time
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Old 24th September 2004, 11:37 PM   #2
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Default Buzz

When it is buzzing, try pushing on the transformer in various placed. If the noise changes, it is mechanical noise (very common). If it goes away do something to simulate your push and leave it there.

If none of this helps, there is some electrical problem (very rare) making it buzz.
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Old 25th September 2004, 01:07 PM   #3
djk is offline djk
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Add a bridge rectifier, from a Bryston 3B schematic.

http://www.diyaudio.com/forums/attac...?postid=328821

If you want to spend money, add the same circuit to the primary side of an isolation transformer and go to balanced power (120:60-0-60).

What causes DC on the mains?

Your NEIGHBOR using a crock pot, a hair dryer, a space heater, or one of those 300W halogen floor lamps on 'low'.

Those devices use half-wave rectification that causes an imbalance in the transformer out on the pole that feeds YOUR house too.
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Old 25th September 2004, 05:07 PM   #4
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DC on the mains is very, very rare. If that was the case, also power amps would be banned. They also pull unbalanced power from the mains, even if a little.
Very likely you have a mechanical issue, the transformer wasn't impregnated correctly or long enough and now there is some 'play' in the core and/or windings. The giveaway is the vague reply by the plitron tech.
This generally cannot be fixed other than by replacing the transformer. You CAN try to tighten the bolts/nuts that fix the transformer (is it a toroid?) but if that doen't solve is (and probably won't) you'r out of luck.

BTW, to check if it is the DC, just get yourself a large (10+ uF/ 400V) non-polarised cap and put it in series with the primary. That will remove any DC.

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Old 25th September 2004, 09:15 PM   #5
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"DC on the mains is very, very rare."

You stated that exactly backwards. Clean AC is very, very rare.

Because of cost issues, and ignorance, BUYERS of toroids don't get what they need to do the job.

"BTW, to check if it is the DC, just get yourself a large (10+ uF/ 400V) non-polarised cap and put it in series with the primary. That will remove any DC."

Just build the Bryston circuit, it will cost about $10 to try it.

"This generally cannot be fixed other than by replacing the transformer."

If it is of an E&I construction you can take it to a transformer/motor repair shop and have it vacume varnished. I would still try the Bryston circuit, Mark Levinson uses it in some of their amplifiers too.
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Old 25th September 2004, 09:34 PM   #6
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Quote:
Originally posted by djk
"DC on the mains is very, very rare."

You stated that exactly backwards. Clean AC is very, very rare.
[snip]

Sure, clean AC IS very rare. But that doesn't mean there is DC. Generally there is lots of harmonic distrotion, noise, spikes (often in the kV area), but not DC.

Jan Didden
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Old 25th September 2004, 09:37 PM   #7
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Quote:
Originally posted by djk
[B[snip]If it is of an E&I construction you can take it to a transformer/motor repair shop and have it vacume varnished.[snip] [/B]

Would that work? I've never thought about that, but it seems a good idea.

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Old 26th September 2004, 02:43 AM   #8
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"This generally cannot be fixed other than by replacing the transformer"


That is a stupid idea, a Chiro amplifier is not a cheap amplifier, and it's power transformer is especially not cheap.

How could you give this poor man an idea like that? His transformer is buzzing, not smoking, I don't like this at all, you must work for Best Buy or Rent-a-Center, when we get a buzzing transformer, let's replace it and throw a perfectly good transformer in the trash! I don't mean to come down on you, but use your head!

Transformer noise can be dealt with, the transformer must be removed from the amplifier and depending what type it is, whether it is a toroid or EI core, if it is an EI core, soak it in shellac and let it dry, then reinstall it in the amplifier. If it is a toroid, try to isolate where the noise is coming from, (it's unusual for a toroid to hum), and fix the noisy winding in place.

I apologize for coming down on you janneman, but your answer of replacing this man's expensive power transformer was unacceptable!
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Old 26th September 2004, 10:01 PM   #9
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Perhaps it is just vibrating against the case. Transformers emit magnetic noise around them when operating and can cause a 60Hz rattle against the case. Try mounting the transformer in the case using some rubber gromets between them to absorb the noise.
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