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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
bigshutterbug
379 posts
 
Yes, a dedicated line is the first step, a good outlet, properly treated room, and correct speaker placement are often the least costly "tweaks" that all add up.
I am using the Signal DU-2 transformer. It is rated at 2Kv and 18 amps as an isolation transformer, and about half that when wired to produce balanced power. Mine ran warm and made an audible hum when wired as an isolation transformer. I did not notice any gains in sound quality running the amp through it this way, but it did reduce the voltage. When I wired it balanced, it runs extremely cool with no audible hum. There was a noticeable change for the better in detail and soundstage, but it was not not quite as dramatic as my previous BPT 3.5 Ultra power conditioner I was running. It sure was a LOT less money though, and my tube amp should last me a long time.
I can send you a diagram showing how to wire it if needed. It is not as difficult as you would think. It only took me an hour or so...
undertow OP
1,033 posts
 
Actually where can you buy that transformer now? Any links? I just hooked up another transformer balanced, yes it is easy, I was just curious what the one you are using looks like. What gauge wire is coming off there? Mostly I noted that even some of the higher power transformers are only in the 22 to 18 gauge range, strange as you would think even though that is enough to carry pretty high amperage mostly for what we are talking about somebody would make one with some at least 12 gauge beefed up wire. Anyway thanks
bigshutterbug
379 posts
 
Mine had no wires coming off of it, just screw terminals with nuts to wire your primaries and secondaries to. You can just do a search for Signal DU-2 transformer and you will find some electronics dealers that either stock or order them for you. Last time I checked, new ones were around $350 plus another $50 for shipping. There is a smaller Signal DU-1 on E-Bay right now for around $150, and a HUGE Signal DU-10 (10kva) unit for $900+ ( this thing weighs 175lbs!). If you wait a while, you can find a used DU-2 on there for a sane price. If you view the picture of the big Signal DU-10 on there, my DU-2 looks very similar to it, but a smaller 65lb version.
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