Amplifier transformer hum: what to do?

[Feanor]

I have tried several amplifiers in my system and they all show transformer hum; (there's no hum from the speakers). Clearly this isn't the fault of the particular amp.

The hum often increase after the time the amp is switched on. If music is played at louder volumes, the hum generally gets more pronounced and stays that way even after the volume is reduced.

= What causes this sort of hum?
= Does it harm the amplifier?
= Does it degrade the music? (I haven't noticed this myself.)
= What can be done about it?

[Beckman]

I have tried several amplifiers in my system and they all show transformer hum; (there's no hum from the speakers). Clearly this isn't the fault of the particular amp.

The hum often increase after the time the amp is switched on. If music is played at louder volumes, the hum generally gets more pronounced and stays that way even after the volume is reduced.

= What causes this sort of hum?
= Does it harm the amplifier?
= Does it degrade the music? (I haven't noticed this myself.)
= What can be done about it?

Transformer hum is caused by eddy currents in the transformers core. Transformer cores are made up of many thin layers of steel and the edy currents cause these layers to vibrate back and fourth. The reason the hum increases with volume is because more current is flowing through the transformer and the eddy currents are incresed. This will not hurt the amplifier in any way. This will not degrade the music. The only way to fix this would be to replace the transformer with a higher quality one. I personally have never listened for a transformer's hum in a piece of audio equipment, and have never heard of anyone saying it is a problem.

[skeptic]

The first thing to do is to find out the real cause of the hum. Transformers themselves rarely cause hum coming through loudspeakers. Most high quality audio gear have well shielded transformers. Most times when there is hum, the source is elsewhere. First turn off the amplifier and disconnect all other equipment including unplugging them from the wall outlets and all antenna and cable TV connections. Turn the amplfier back on. If there is still a hum, try placing the amplifier someplace else. Sometimes direct induction of stray 60 cycle fields occurs. I saw this once happen to an amplifier sitting on an aluminum bridge table. When we lifted the amplifier, the hum went away. If there is still hum, the amplifier may need repair. The problem may be with a large electrolytic capacitor in the power supply used to filter hum, not the transformer. If there is no hum, turn the amplfier off and reconnect one piece of equipment. Then turn it on to see if the hum returned. Keep repeating this process one piece of gear at a time. Sooner or later when the hum returns, you will find the real cause. That will indicate the remedy. Common causes of hum in audio systems are poor cable routing and inadequate shielding, especially for phono cables, improperly grounded turntables, and ground loops from cable TV antennas or multiple wall outlets on different circuits. Don't spend any money on tricky expensive fixes until you determine the cause. Most uninformed wild guesses turn out to be wrong and the money spent to cure phantom causes that actually don't exist is wasted.

[Beckman]

The first thing to do is to find out the real cause of the hum. Transformers themselves rarely cause hum coming through loudspeakers. Most high quality audio gear have well shielded transformers. Most times when there is hum, the source is elsewhere. First turn off the amplifier and disconnect all other equipment including unplugging them from the wall outlets and all antenna and cable TV connections. Turn the amplfier back on. If there is still a hum, try placing the amplifier someplace else. Sometimes direct induction of stray 60 cycle fields occurs. I saw this once happen to an amplifier sitting on an aluminum bridge table. When we lifted the amplifier, the hum went away. If there is still hum, the amplifier may need repair. The problem may be with a large electrolytic capacitor in the power supply used to filter hum, not the transformer. If there is no hum, turn the amplfier off and reconnect one piece of equipment. Then turn it on to see if the hum returned. Keep repeating this process one piece of gear at a time. Sooner or later when the hum returns, you will find the real cause. That will indicate the remedy. Common causes of hum in audio systems are poor cable routing and inadequate shielding, especially for phono cables, improperly grounded turntables, and ground loops from cable TV antennas or multiple wall outlets on different circuits. Don't spend any money on tricky expensive fixes until you determine the cause. Most uninformed wild guesses turn out to be wrong and the money spent to cure phantom causes that actually don't exist is wasted.

"I have tried several amplifiers in my system and they all show transformer hum; (there's no hum from the speakers)."

There is no hum from the speakers.

[skeptic]

If you are referring to a mechanical hum due to vibrations of the transformer itself, it is due to loose mounting hardware or lack of damping from rubber bushings, or internally loose construction of the transformer itself.

Why do transformers hum?

Because they don't know the words.

[Beckman]

Why do transformers hum?

Because they don't know the words.

...

[Feanor]

If you are referring to a mechanical hum due to vibrations of the transformer itself, it is due to loose mounting hardware or lack of damping from rubber bushings, or internally loose construction of the transformer itself.
....

What I hear you saying is that all four amplifiers I have tried are poorly mounted, poorly designed, and/or poorly made transformers. That would included my brand-new Bel Canto eV02i, and the relatively new NAD C270 it replaces. This is truly unhappy.

What do you suggest I do? I don't think I want to keep trying different amplifiers, most of which would hum, I suspect.

[uncooked]

i had the same problem with one of my receivers about a month or 2 back. even when it was off it was making a hum like the sound high voltage power lines make. i put it onto a outlet with no other equipment on it, and also a power bar. "a cheapy, probably 20 bucks" with nothing else plugged into it. and its worked fine ever since no hum.

[Feanor]

i had the same problem with one of my receivers about a month or 2 back. even when it was off it was making a hum like the sound high voltage power lines make. i put it onto a outlet with no other equipment on it, and also a power bar. "a cheapy, probably 20 bucks" with nothing else plugged into it. and its worked fine ever since no hum.

I've move both power cords and interconnects around, but the problem hasn't gone away. I think the solution might require for a dedicated line for the hifi equipment.

But what about power conditioners and/or an isolation transformer??

[uncooked]

u might as well give it a try, buy a power bar conditioner, and if it doesnt work take it back.

[Feanor]

[QUOTE=Feanor]I have tried several amplifiers in my system and they all show transformer hum; (there's no hum from the speakers). Clearly this isn't the fault of the particular amp.
...QUOTE]

I guess it doesn't get to the root cause, the quality of the AC supply as suggested by Beckman, but it seems to suppress the symptom. I placed my amp on a set of three Gutwire NotePads, one of them directly under the transformer. I now hear no hum at all.

The NotePad is basically an "audio grade" gel pack. It serves to dampen vibration whether external or internal to the device where its deployed. In my case it seems to dampen the transformer as it begins to hum, effectively suppressing the hum altogether.

BTW, my new Bel Canto is sounding great after its initial burn-in. It's a very substantial improvement over my previous Apt Holman/NAD C270 combination. Sometimes you get what you pay for!

Thank you all for your advice!

[boba]

often the cause of audio amplifier transformer hum is DC current in the AC line. This DC current mixed in the line causes the plates in the transformer to rattle. Usually the problem is not the transformer. Not sure how, or why DC current gets into an AC line, but it does. There are power conditioners to use, PS Audio Power Plant is one. If the hum is not a grounding issue, nor from another electrical device it is almost certain to be from DC current in the line.

[JohnMichael]

often the cause of audio amplifier transformer hum is DC current in the AC line. This DC current mixed in the line causes the plates in the transformer to rattle. Usually the problem is not the transformer. Not sure how, or why DC current gets into an AC line, but it does. There are power conditioners to use, PS Audio Power Plant is one. If the hum is not a grounding issue, nor from another electrical device it is almost certain to be from DC current in the line.

Thanks for your input almost 11 years after the post. I hope the problem was previously resolved.

[Feanor]

Thanks for your input almost 11 years after the post. I hope the problem was previously resolved.

Thanks, JM. The Bel Canto amp with the transformer hum is long gone. Most of my current equipment, including my Pass Labs amp, is silent; there is no hum through the speakers. The only exception is my Belkin PF60 surge protector/power filter which has a slight hum you can hear if standing closer than about a foot away.

BTW, I don't recommend the Gutwire NotePads I mentioned earlier in thread; the gel inside eventually dried out. The good news, though, is that they didn't leak and cause a mess