Help I think my AC is polluted

I have had similar experiences that occur when line voltage is low. I have 2 Arcam amplifiers and came home one day after dark around Christmas when all the houses were lit up with Christmas lights. Both of the amplifiers transformers were humming loudly. Scared the heck out of me. Unplugged the equipment and hooked it back up the next day. No hum in the transformers, everything fine. Later in the day when all the Christmas lights started coming on, back came the transformer hum.

Talked to the local dealer who sold me the amps and they had experienced the low line voltage problem when they first opened. After some research they had isolated the low line voltage and were able to make the local power company adjust the transformer feeding their shop. In our area (Cincinnati) the power company has responsibility to maintain a minimum working line voltage.

In my neighborhood the power transformer that feeds our house blew up shortly after that, and I never got to confirm the low voltage with meter readings or to request the power company check the voltage. I haven't experienced the transformer hum problem again with the replacement by the power company.

Not sure it is the same issue you are having, but just something I had experience with.

Jim S.

since you have the system on dedicated circuts shut off all the other breakers in the house one at time (when the hum is active and with your system on) see if you can locate the hum to something in the house.
imho i think the problem is coming from outside the house

Thanks for all the quick responses. I'll try to answer all your questions in order.

Kr4 - Presently I don't really have a way to run the system on battery power. If I go in that direction, is there a product on the market that can power my entire sytem?

Nsgarch - Yes. It occurs whether using the CD player or tuner as the source. A power regenerator may be the answer, although I'd rather go to the source of the problem. I've also read that a power regenerator may inhibit current flow and dynamics depending on the system. What did you find with the ExactPower.

Tbg - When I have the hum, nothing I do can change it. What makes me pretty sure it's dirty AC from outside the house is yesterday I disconected everything from the Equi=tech and still had the hum when I put my ear up to the conditioner while powered up and on standby. Today it's gone and the Equi=tech is dead quite. I'm not quite sure how to scope a line. Can you give me more info on that?

Stilljd - You may be right about low voltage. I've been living here for six years and we used to get quite a bit of power surging. I would often see the lights brighten and dim at night. I haven't noticed this recently though. I will complain to the power company and see where it gets me. The odd thing is the hum happens on the weekend and that's when the power grid should be cleanest. Unfortunately, it's also when I have most free time to listen to music.

Hotpanley - I will try your suggestion but given the two week intervals between this problem, I'll be surprised if it's something within the house.

I appreciate all your responses to help solve this problem.

Happy listening, Mike

All transformers will hum to some extent, since they are being energized with AC. Audio tranformers are designed for 50/60 cycle operation and are designed and mounted to be as quiet as possible. One would expect those with iron cores mounted on a heavy chassis to be the quietest, as opposed to those without iron cores mounted on a light chassis.

The transformer/chassis combination is subject to resonance just like any material. If the external power is contaminated with large amounts of repetitive noise, one would expect the transformer noise to increase, especially if it gets near a resonant point. Also, sources of external AC noise can be very intermittant, such as air conditioners, industrial pumping, maintenance cleansing etc., which can explain your symptoms.

A really good solution to this is an isolation transformer on the AC mains ahead of the fuzes to the dedicated lines (e.g., a 4-5kva Topaz). The iso has the advantage of reducing common and transverse mode noise by up to 120db, eliminating any DC on the line, and blocking large voltage spikes. Some iso's also have additional taps to raise or lower the output voltage, if that is a problem in your area. Consider this approach as well as the power conditioners you are looking at.

Zargon - Thanks for the informative post. What is the cost of an isolation transformer such as the Topaz? How much work is it for an electrician to install? I had one hell of a time getting an electrician to do two dedicated lines. Would this be a better/more cost effective solution than a power regenerator?