Amplifier Hum - A Problem Solved
I thought I would post this hoping it may be helpful to someone troubleshooting amp hum or buzz.
I have a Belles 150A Reference amp. It always had a little hum from the transformer, but nothing real loud or what I thought was out of the ordinary. Funny thing is, the hum was always loudest either early in the morning or late at night; times when you would think the grid was cleanest. The hum was never sent to the speakers.
I do have three dedicated 30A circuits. It didn't seem to matter which circuit
or which combination of equipment was plugged in where; still that same hum and most noticeable at those certain times of the day.
About a week ago, I received my new pair of Belles MB-200 mono-blocks. I cleaned up my rack, created some room, and by 8 o'clock had those babies plugged in. No hum. Glorious. By 10 o'clock the hum was back and 5 times louder than my other amp. WTF! I started plugging into different circuits, tried unplugging everything but the amps. HUM. The hum on the mono-blocks was much louder than on the 150A-they have a much larger transformer. It was getting late, so I turned them off and went to bed. Early the next morning, I turned them on - no hum. Later that morning I called my electrician, explained my problem, and asked him if there was any way that noise could get into those circuits or if the grid could cause that much noise. He didn't think so. (We live in a rural area with no industry and always had, what I thought, was pretty clean power.) He said voltage fluctuations can cause torroidal transformers to hum and asked me to take some readings on my voltage at different times of the day. I have 123V morning, noon and night.
I talked to a number of other people about the problem. Most said power conditioning. I knew I had "dirty power", but I just had a feeling that this problem was not going to be solved by a power conditioner.
This past Friday night I had the house to myself, so I was going to do an extended session. About 7 o'clock I turned everything on and by 8 I was cranking. My system had never sounded so good. Of course, there was no hum. I listened to well past midninght. I was excited. The gremlins had left. Or so I thought.
I awoke Saturday morning and immediately went to my listening room. No hum.
About 9 o'clock that night, I sat down to see if I could get a repeat performance of the night before. No such luck. The Gremlins were back and they had brought friends. The hum was louder then ever. I could hear the "swarm of bees" from 15' away. My wife was on the computer, so I had to do my searches on my iPod touch. I went to the Audigon forums and did a search for "transformer hum" and "amplifier hum". I learned a few things. Torroidal transformer hum can be caused by voltage fluctuations (which I do not have) and stray DC current. Stray DC can pollute the whole panel; it is not circuit specific. So I wandered around the house thinking DC current? DC current? I don't think I have any DC fixtures or appliances in my house.
I walked into the kitchen and there it was staring me in the face-the soft illumination of under-cabinet lights. I rushed to the switch, turned them off and ran back to my listening room. NO HUM. I ran back to the kitchen, switched the lights back on, ran to my room. HUM. Laughing hysterically, I ran repeatedly between the rooms switching the under-cabinet lights on and off (Hum, No Hum). Then I thought, why is the hum so much louder tonight than other nights? So I stared at those damn lights until I noticed that they were dimmer than usual. I checked the individual switches on each light and sure enough my wife had switched them all to low (must have been that evening). So now I'm running back and forth switching those lights on-high, switching on-low, switching off (Hum, Loud Hum, No Hum).
So there you have it. Something as innocuous as under-cabinet lights can cause real problems. The light is so subtle and pleasant that I just overlooked them as the "Cause". My wife always turns them on later in the evening, and since I'm an early riser I'll turn them on early in the morning, hence my amp hum at those times of the day I mentioned above. The lights in question are the 12V xenon under-cabinet lights with an electronic transformer. I am a custom home builder and I have unwittingly polluted a lot electrical panels. These types of lights are extremely popular. We audiophools are few and far between, therefore I have not had any feedback from clients with similar problems.
I want to do some really neat 12V or 24V lighting in my listening room, but now I am having second thoughts. I have read that the more expensive magnetic transformers do not have the problem of stray DC current "back charging" the whole panel. Any thoughts on this?
My audio habits have been a source of friction between my wife of 29 years and me. Now I have to add one more to the list: "Honey, I'm going to listen to music for a little while. Could you leave the kitchen lights off?"
I hope this helps someone down the line.