Is it possible for the power fed into an Amp to cause the amp to buzz/hum? - AVS Forum
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post #1 of 7 Old 11-15-2013, 01:52 PM - Thread Starter
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I purchased an emotiva xpa-5 at the beginning of last month and sent it back the other day because it had a buzz/hum from the speakers that I could hear at my listening position about 10' away. The unit itself had a vibration and buzz/hum but it was faint.
I don't think this was a ground loop, I tested with just the speakers hooked up and one rca to mini connecting the front L/R to my cell phone and it still had the buzz/hum.

So, I somewhat assume there is some type of internal grounding issue in this amp but I am curious if there is some type of power related issue that could cause this type of problem. I did test the amp plugged into another plug and circuit in the house as well.
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post #2 of 7 Old 11-15-2013, 02:10 PM
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Toroidal transformers have been known to buzz. They are usually dipped and rubber mounted to isolate them from the chassis to minimize this though.

It's not out of the realm of possibility that there is DC voltage on your AC line voltage, this is usually a bigger problem for the power company transformer than it is for the gear in your house though.
Most equipment has power factor correction built in so even if there is some DC on the AC line it should not cause a buzzing problem.

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Charlie

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post #3 of 7 Old 11-15-2013, 02:24 PM - Thread Starter
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Would that buzz bleed into the speaker output? I may not have been clear the amp had a faint buzz/hum but the problem was that the speakers were producing a buzz/hum that could be heard at my listening position.
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post #4 of 7 Old 11-16-2013, 05:07 PM
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Sorry, you wrote the question correctly, I misunderstood.
No amplifier should produce an audible buzz through the speakers.
If you have no input signal and the volume is set to max you may hear a very faint hiss (and I do mean very faint) right next to the speaker, never a buzz or anything else audible at 10 feet.
Since this particular one physically vibrated and had a problem you heard out of the speakers it was a dud.
What other gear do you have?
Oddly enough if you have an AVR that is high enough up the food chain to have pre-outs 99.9% of the time external amps are not needed.

Regards,
Charlie

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post #5 of 7 Old 11-16-2013, 06:04 PM - Thread Starter
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I am using a Yamaha 7065( http://usa.yamaha.com/products/audio-visual/av-receivers-amps/htr/htr-7065/?mode=model) to drive some Polk LSiM that are 88db efficient. It's 95 watts it sounds anemic compared to the Yamaha 820 running in another world. I got the external amp just to ensure it wouldn't clip when up at reference volume.
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post #6 of 7 Old 11-16-2013, 07:42 PM
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It's probably DC in the AC line causing speakers driven by power amps to buzz. I have this issue in my home so I am stuck using receivers as all power amps cause audible buzz through speakers from several feet away. So I just get the most powerful receiver I can find instead.
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post #7 of 7 Old 11-20-2013, 06:41 AM
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I have seen this happen before with a PA setup. I am not sure if the buzzing noise came from the amps or from the other gear in the setup. When we opened the circuit breakers in the building except those feeding our rack, the buzzing stopped. We still don't know what caused it.

Our fix was to use a online (aka double conversion) UPS and feed everything off that. I figured that if I only used amps with switch mode power supplies the UPS would be OK with it. I wouldn't dare to try this with an amp with a big transformer in it because it would pull allot of current out of phase which the UPS would not be able to handle. (read: blow up)

We used a second hand MGE Pulsar, while the batteries are likely worn out it did do the job and provide our rack with clean power.
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