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amp hum :( Faulty ac power?

Donny

Donny

Big Damn Hero
I have a mcintosh ma252. I have recently noticed a hum that wasn't there before. The hum come and goes. I would have thought this to be the amp except I had the same problem with a vintage receiver awhile back. The vintage unit had the problem in the same room and in another room that I tried in the house.
I checked the breaker box to ground and that looks fine. I am now wondering if it's the power coming into the house. If so would a power conditioner help?
 
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If you can trace the hum to the amplifier you can then use something similar to stethoscope to check the transformers. If you can hear a hum or buzz in a transformer the transformer itself can be faulty or you could have DC present on the AC power line. Many (most?) power conditioners have a circuit designed to remove DC from your AC power, or you can purchase an add-on device made for that purpose, such as the Emotiva CMX-2 which is inexpensive and really works!

Ask me how I know :thumbsup:
 
CFL's and other appliances might be the culprit especially if there was no hum before. It might be time to replace capacitors if the hum is volume independent.
 
I would hear hum from time to time, finally realized it was noticeable when the air compressor was cycling (220) far in another part of my space. I went to grounded power cables and it went away. Can’t say why but it worked.
 
Check if anything else in your setup has changed - ie: do you have grounded and non-grounded appliances plugged into the same power outlet/circuit?

Does the hum continue with no input source connected?

If the above items check out OK then I would next look at internal issues - Ie: powersupply caps as others have suggested
 
I did try disconnecting the source. Same hum.
The mcintosh is new as in only a few months old.
I am considering a power conditioner. That Emotiva CMX-2 sounds interesting.
 
Donny said:
I did try disconnecting the source. Same hum.
The mcintosh is new as in only a few months old.
I am considering a power conditioner. That Emotiva CMX-2 sounds interesting.
Click to expand...

You said in your OP that the hum comes and goes and that it's happened with a receiver and your McIntosh. I experienced a similar problem. A long distance diagnosis is very difficult if not impossible, but you very well could be getting intermittent DC voltage through your AC mains, which would cause a transformer hum in your amplifier. I have a power conditioner that I like, but found out that it lacks the circuitry that eliminates DC voltage on the AC line, but I wanted to keep it so I went for the CMX-2 and it worked for me. I'd advise you to give it a try if you can rule out the other possibilities. I think I paid under $100 a few years ago for mine.
 
Keep track of what's turned on or running in the house when you hear it. If it will stay on long enough, go around turning things off one by one - including unplugging the refrigerator, etc.

You can also try a ferrite bead on the power cord although that's more for RF noise (hash) rather than hum.

Make sure your interconnects are not laying next to power cords.

BTW AC power is 100% hum - at 60 Hz that is. If hum is getting through the amp's power supply, that's a fault in the power supply. Just as likely it's coming through the air from somewhere, or from one cable to another behind your setup.
 
I have noticed that the hum tends to go away at night... It's cool enough outside not to need air conditioning this morning. No hum this morning. I think maybe a neighbors ac is feeding back through the ac lines,if that's possible.
 
Very possible for appliances or other stuff to feed back noise into the lines. Certainly not the first time I've heard of this kind of thing. Question is whether there is anything else amiss that is allowing it to get through into your house, or it's just unavoidable. In which case the gadget should take care of it.
 
DC in the AC line can cause hum in the transformer(s). If you do not hear hum through the speakers (at the same time), there is a good chance that this is the problem. The Emotiva cmx-2 is one device that can eliminate this problem. I run one of these in my vinyl room. There is no hum problem. Audio by Van Alstine also has one called the Humdinger, that may work well for this problem.

The cause of DC in the AC lines is from poor power supplies in various electronics that may be in the house, and might be from one particular device. You offered some clues to this fact that it went away at times and then returned. I suggest that the next time it happens and you don't get the cmx-2, go around your house and start disconnecting things from the outlets.

Remember that many devices are still on even when they are off, like a TV or garage door opener, waiting to receive a code from the remote. Wireless phones, kitchen and laundry room appliances, maybe even a dimer for lights could be a culprit.
 
We have sold many HumDingers to McIntosh owners. It is specially effective if the McIntosh is used in a HT system with a plasma TV. Plasma TVs are notorious for putting low level DC on the adjacent power lines. The HumDinger is only $140 and you can return it if does not cure your problem.

Frank
 
How do these gadgets actually work? Usually to block DC in a low power circuit you can just use a cap. Is it a big cap that passes 60 Hz with no impedance or is it something else? Just curious to learn.
 
avahifi said:
We have sold many HumDingers to McIntosh owners. It is specially effective if the McIntosh is used in a HT system with a plasma TV. Plasma TVs are notorious for putting low level DC on the adjacent power lines. The HumDinger is only $140 and you can return it if does not cure your problem.

Frank
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I happen to have a plasma tv...Thanks for the heads up!
 
I received the cmx-2. It show no fault on the ac current. It however did not stop the hum :( I'm going to neaten up my cables in hopes of resolving my problem. Then I will look into the humdinger
 
Sounds like your AC is using a two wire system with out the 3rd wire and you may have a bad connection to the neutrals. If the neutrals are Ok and you have copper water pipes you may want to ground the system to the water pipes or drive a 8 ft ground stake and connect a number 10 or 8 awg wire to the system. If you have very efficient speakers. you might need Mac Quad SS balanced amplifiers to gain an extra 20 db signal to noise.
 
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twiiii said:
Sounds like your AC is using a two wire system with out the 3rd wire and you may have a bad connection to the neutrals. If the neutrals are Ok and you have copper water pipes you may want to ground the system to the water pipes or drive a 8 ft ground stake and connect a number 10 or 8 awe wire to the system. If you have very efficient speakers. you might need Mac Quad SS balanced amplifiers to gain an extra 20 db signal to noise.
Click to expand...
thinks it is next doors aircon causing the problem .. no idea about fcc rules .. probably does not apply here .
 
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