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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
jea48
4,764 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.
Post removed 
hevac1
812 posts
 
Guys do not forget it is going to cost money just to power the coils of these items, even with no load. Also most transformers above 1kva will not like being turned off & on and can trip breakers on inrush. It is better to leave them on all the time but again at a cost.

I had a GE 5kva 240vac to 120vac balanced center tap transformer and it drew 5 amps just charge the coils on power up with no load. I was told by the GE that the draw is normal. I even tried switching it on and off via a starter but it tripped the 40 amp breaker 3 times out of 10. I wanted to try fuses but the type required cost too much to risk for testing, $30 each 5 minimun per order, they are used in most VFD's.

Too much cost for me, I use PS Audio equipment if I need volt or Hz control. It may cost more but they worked out the bugs and it can be turned off & on at will, by button or the new ones by remote.

I did not read all the issues here but Variacs do not change hertz only voltage and can hurt the a/c motor on your TT if connected to it.
gbart
290 posts
 
Jea48, after posting I did some research and found out that ANSI Standard C84.1 covers residential voltage regulation in North America and that the limits are ± 5 percent of 120V.
undertow OP
1,033 posts
 
My Results:
Okay so the Balanced transformer does not seem like a bad thing! Meaning for the little I got to test listen it did not seem to remove anything from the music or overall dynamic presentation, however what it did do was remove a slight amount of "Anxiety" maybe in the presentation… Seems to have very slightly laid back the soundstage where it moved backwards about a foot and became about a foot wider, might have a little better balance from left to right so to speak.

Vocals have a bit of a more left right quality of being less accurate and more blended with air, the bass is VERY tight, it may have literally made the low frequencys lose a little of the Bloat and more of a dynamic yet buttery type punch, more cushion if that makes sense. There is not a final verdict, but its pretty cool! Worth the money?

Very tuff to justify something like this one way or the other, its worth it due to knowing it has an effect to the AC power in the house whether its gonna be detrimental or beneficial depends on a lot of things… In this case I would say I give it a 5% effective rate, that means a bit better control and distortion is minimized even further, for 5% at this level it costs money because there is very little you can do to make perfection, and this system was damn good already so just a little bit is nice but maybe not gonna make miracles..

For the time being I am of course happy with it, I like having it, and it does solve one Ergonomic problem that is not a big deal but being picky, it gives me ONE power switch to turn on and off the amps without opening 3 doors on my unit everytime! Anyway and of course the pride of ownership, and I upgraded the CRAP out of it last night removing the ground shunt capacitor pack setup in it to the AC recepticals, and put in buss bars replacing the cheap terminal strips… I am told these ground shunt filters are great for eliminating common mode noise but can end up being a downside to audio applications robbing you of some dynamics and they are somewhat dangerous if they fail and you don't have a GFI outlet connected to it… From what I am told these shunt filters if one cap fails and there is no GFI outlet your done.
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