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Variac vs. Isolation vs. Balanced Transformer? ALL

Hi,
I am looking into the different types of power transformers to fix a few things.

First is a slight hum from speakers using Class A ultra wide bandwidth amplifiers, caused by common mode noise between the Ground and neutral lines from my understanding.

This is not really all that critical as its well under noise heard 3 feet away, but we are picky otherwise we would not be on this site!

Second and maybe even more important is I am getting a pretty continuous 128 volt output from all my outlets. I would like to use a product or build one to step this down to the best possible 117 volts or so for most gear.

I see many variacs for about 100 bucks on the ebays etc... That can do at least 500 watts or 5 amps each.

I was considering just buying about 3 of these one for each mono block would cover the amps, and one or 2 more for the source components.

Anyway that's really the basis of the question, I will not pay 2000 for a used or new piece of gear, like a regenerator or powerplant etc...

I do not want to restrict the dynamics to the amps or other gear.

And I can not put just one unit at this point due to running power cables are in 3 different spots in the room and I will not be running 15 ft power cables all back to one point. Also due to the fact I prefer to split this all up over 2 or 3 circuits in the house anyway.

So where to go?
I see Balanced transformers, are these considered "Isolation" transformers as well? Also will these automatically put out a continuous voltage at the 115 to 117 range? Or would you still need a variac to adjust to the needed voltage and frequency?

Thanks
undertow

Showing 1 response by zargon

zargon's avatar
zargon
453 posts
 
I would stay away from Variacs. Five in a room would make more noise than the current noise level you are trying to eliminate, generate a good deal of heat, and you would never get the voltages the same across all equipment without constant fiddeling.

To both reduce hum and reduce the voltage, I suggest you run consider a subpanel driven by a 4 or 5 kva isolation transformer, with 2 or 3 star grounded dedicated circuits. Many of these isolation transformers have taps on the secondary to allow you to adjust the voltage output and can reduce common mode noise by up to 120 db. They can be found used in electical surplus houses for under $500.

See my system as an example.
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