How much transformer hum is normal?

John Garcia · 10-03-2005, 01:01 PM

I got my brand new Marantz PM-7200 about 2 months ago. It sounds great, but recently I noticed what sounds like transformer hum. I put my ear up to all my other amps/receivers and they all hum, but the 7200 is audible from across the room when nothing is playing. I disconnected everything from it, and the hum is still audible. My dealer said they would swap it out, but what if the new one is exactly the same? Should it be quiet or is this normal?

Leo Kerr · 10-03-2005, 03:53 PM

My general impression is that when you have nothing (including speakers) plugged into it, you should not hear the amplifier!

Not unless it was, say, 2kw/channel and needed a serious power supply with 480v input...

ColinM · 10-03-2005, 03:59 PM

Should be silent from 3 feet, my personal rule. I don't have anything right now that violates that rule, and in all cases, are lesser gear than the Marantz you have.

JackS · 10-03-2005, 06:22 PM

John- What you might be hearing is a high speed rattle caused by the power supply. I've seen others post this question in the past and a few have gone to extremes to get rid of it.
Since your receiver is new, I wouldn't advise that you open it up but, one thing you might try is a slight tightning the case screws.
A longshot maybe, but easy to do and doesn't void your warranty

John Garcia · 10-03-2005, 07:19 PM

I put my hand on the case to see if it stopped, and it didn't I put my ear up to the case and it is definitely an electrical sounding hum from one particular spot, but it is not audible through the speakers. I will try that though, thanks.

While all of my other amps/receiver hum (Marantz 8300, 2X MA500 monoblocks, Audiosource Amp One/A), it is only noticable if you stick your ear right up next to them, which is the main reason why I noticed this one being out of the ordinary. I also didn't notice that hum when I initially purchased it, and that was while I was doing a LOT of critical listening with it. It doesn't matter if I have it in class A or AB, it does the same thing, even if I have both speaker outputs turned off.

I currently have the Amp One swapped in place of the PM7200 and there is no hum.

Thanks guys, I will most likely have them swap it out for another and see what the new one does.

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Wayne Ernst · 10-03-2005, 08:13 PM

John,

Do you have any friends who own a Monster power conditioner that you could try? It would be interesting to see what the transformer does in relation to the hum.

Also, what if you were to take the receiver to a friend's house and plug it in over there to see if the hum exists?

Shiu · 10-03-2005, 08:29 PM

All transformers hum, but as Colin said, you shouldn't be able to hear it from 3 ft away.

John Garcia · 10-03-2005, 10:19 PM

Quote:

Do you have any friends who own a Monster power conditioner that you could try? It would be interesting to see what the transformer does in relation to the hum.

I have it on a Panamax M8-EX. I'll try it on my 5100, but I doubt it will make any difference.

John Garcia · 10-04-2005, 10:01 AM

As I thought, no difference on the 5100.