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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
gbart
290 posts
 
Undertow, you raise an interesting point about the relationship between line voltage and bias. I have high line at my house and its something I've taken into account when adjusting the bias of my amps. I don't understand though why gear should sound best between 115-118V when its designed to operate on 120V. In stock form, final bias readings would be set at the factory with line voltage held firmly at 120V, and obviously the amp should perform best at that voltage, not something lower.

Regarding the balanced isolation transformer, I don't understand why you would get a 5% loss just from going through it unless it has been designed that way. I have worked with quite a few different isolation transformers of various brands over the past few years. All of them in stock form start out with some percentage of no-load boost, not loss. I have ordered transformers and specifically asked that they be wound without the boost, to compensate for the high line at my house. A decent, appropriately sized transformer with good regulation should not lose 5 percent under load.
undertow OP
1,033 posts
 
Gbart, well hopefully there is no loss! But for some reason there is a claim of up to like 5% maybe saturation or something with most transformers? Still it should be better due to obviously cutting the voltage in half on and spreading on 2 phasesÂ… As for sound in the lower voltage range they are not really designed to be on 120 from my understanding, but most is tested on the lower range of 110 - 115 v. However as for sound the higher voltage I believe adds certain noise at certain frequencys in the line. The U.S. standard for the most part is 120 volts, and the fact is they have to be able to spike to 130 I guess.

No real scientific reason on my end this is just what I have normally experienced so some type of regulation beyond just saying okay whatever I am being fed from my garage on the circuit box is good enough seems a little off now having high grade power supplys in each audio component.
jea48
4,668 posts
 
Gbart, well hopefully there is no loss! But for some reason there is a claim of up to like 5% maybe saturation or something with most transformers? Still it should be better due to obviously cutting the voltage in half on and spreading on 2 phasesÂ…
I might be wrong, but if you feed the transformer with 128V you are going to get 128V out on the (2) hot ungrounded secondary leads. Just because the center tap of the secondary winding will be connected to ground will not have any effect the output voltage.
undertow OP
1,033 posts
 
Jea48 actually this is a "Balanced transformer" so it will output if there is no loss 128 volts / 2 = 64 volts to the hot and 64 volts to the neutral on the duplex.
jea48
4,668 posts
 
06-03-09: Undertow
.... actually this is a "Balanced transformer" so it will output if there is no loss 128 volts / 2 = 64 volts to the hot and 64 volts to the neutral on the duplex.

Balanced is a fancy word for split phase..... The same type of transformer the utility power company uses to feed your home. (120V 0 120V)

128 volts / 2 = 64 volts to the hot and 64 volts to the neutral on the duplex.
Equals 128V.... The center tap of the secondary of the transformer is the neutral and it is connected to ground.
The two wires that will connect to the power contacts of the receptacle are both hot. Neutral from the transformer does not come into play. The equipment ground of the GFCI receptacle will connect to the same point as the grounded neutral conductor.
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