Low hum in amp.

amplifiers, receivers and loudspeakers
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dancinnyc
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Low hum in amp.

Post by dancinnyc » 21 Jan 2020 01:29

HI, I have a low hum on my McIntosh mc275 tube amp (1972). dose not increase when you add power output ,not really noticed when listening . any ideas? Thanks Dan

chgc
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Re: Low hum in amp.

Post by chgc » 21 Jan 2020 03:20

If you put you ear next to the transformers, does that seem to be the source?

lenjack
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Re: Low hum in amp.

Post by lenjack » 21 Jan 2020 17:49

Try reversing the power cord. Call McIntosh for advice.

dancinnyc
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Re: Low hum in amp.

Post by dancinnyc » 22 Jan 2020 20:25

chgc wrote:
21 Jan 2020 03:20
If you put you ear next to the transformers, does that seem to be the source?
Hi, Yes all (3) transformers have a low hum. I hooked-up a dynaco st-70 & had no hum in the transformer. Sorry I got back to you late. I was trying different combos of amps & pre-amps. The mc-275 has the same hum with any pre-amp I used. Guess its in the transformer or the power supply. It is going on 50 years old. Do you have any ideas? Thanks Dan

dancinnyc
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Re: Low hum in amp.

Post by dancinnyc » 22 Jan 2020 20:36

lenjack wrote:
21 Jan 2020 17:49
Try reversing the power cord. Call McIntosh for advice.
Hi Lenjack the power cords in the 70's were not polarized. You can plug them in both ways, no difference still have a hum. Thanks Dan

lenjack
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Re: Low hum in amp.

Post by lenjack » 22 Jan 2020 22:04

"Yes all (3) transformers have a low hum." That's not really hum. That's mechanical vibration., caused by laminations in the transformers. It should not be coming through the speakers, and you say you don't hear it when listening to music, so it's probably best to put up with it.

dancinnyc
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Re: Low hum in amp.

Post by dancinnyc » 23 Jan 2020 00:18

Yes its not a distraction when playing . Just never noticed it before. Thanks Dan

trevortron
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Re: Low hum in amp.

Post by trevortron » 26 Jan 2020 20:15

If it is mechanical 'hum' from the transformers you might reduce it somewhat by simply placing the whole amplifier (or its feet at least) on something soft to absorb the vibrations & prevent them being transmitted to the surface it is standing on - which will be acting like a soundboard.
I have tinnitus and I find any continuous noise unbearable after a short while. I run a NAS near my workbench and it hums so I simply sat it on some old packing foam and the noise all but disappeared.
If you want to go a bit further and silence the transformers themselves you could try what I did in the mid 80's with a Commodore 64 power supply. It buzzed like hell when it was warm so, with nothing to lose I prised it open and 'dunked' the transformer in a runny varnish/thinners solution (while hot) removed it later & let it dry out. After that, not only was it completely silent, it also ran a lot cooler.

dancinnyc
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Re: Low hum in amp.

Post by dancinnyc » 26 Jan 2020 23:09

Hi, sounds cool ,Iam using my dynco ST-70 amp right now, it's a great amp. I'll get back to the mc275 later. Need some time to see the difference. May sell the Mcintosh Prices are really good now. Thanks Dan.

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