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
Oh and it seems most variac deals are a type of Brush run motor, due to needing brush replacements on some of them, this would mean to me they make some noise… That will not work, I would rather have a passive type method to accomplish all this anyway if possible, but I guess for the most part iso and balanced transformers will be the only possible way while stepping up and down voltage in the process.
Oh and it seems most variac deals are a type of Brush run motor, due to needing brush replacements on some of them, this would mean to me they make some noise…
No, they're not a motor at all . . . they don't move (unless you like to twiddle the knob constantly while you're listening). It's not the brushes themselves in a DC or "universal" motor that cause noise, it's the fact that they're constantly making/breaking connections across a spinning commutator.
i had a slight hum from my system that was eradicated by the use of a bpt bp3.5 signature. the bpt also lowered the overall noise floor. obviously, ymmv.
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.
Thanks Zargon!
Yeah sweet system you have there. I would love to just go all Dedicated like that, but for the time being I am looking to keep the system self contained and moveable vs. hardwired built in. I will have to take advantage of existing circuits for the time being. it
Undertow, although on the high side, 128V is within the ± 10% utility company voltage tolerance in North America. The voltage at my house has always varied between 121.0V and 124.5V depending on the time of day. Coupled with the small no-load voltage boost from my isolation transformers around 1.5% and I'm typically looking at peaks of around 126.4V. I once called up the manufacturer of my equipment to enquire about maximum tolerable line voltage and was told not to worry, that the components are designed to tolerate up to 130V with no problem.
Gbart, You are absolutley right… They are built to tolerate 110 to 130 volts… However that is not the range they sound best in! For sure the best sound comes from most gear in the 115 - 118 range… Mainly this is due to circuits sound more hyped up or "Grainy" with higher voltage mostly from amps bias being thrown off, gotta remember this gear is built and tested on a bench running a variac of sorts feeding them dead on dialed in voltage for testing. I have heard regenerators and even cheaper monster power centers (yeah the ones with the cheesy red digital readout) sound pretty good when knocking that voltage down.. The higher the voltage the less beef you get it seems, thinned out, less amperage, bass is not as strong, and most people complain their gear sounds bright but its simply the wall outlet is really high!

Trust me I had one time solid state amps that had manual adjustable bias banks on the transistors.. I was running about 126 volts from the wall… Brought the bias MA into range to counteract it and bam they went from ragged, tipped up mid fi sound to nearly the best smoothest balanced gear I had experienced! Now of course this was not a solution, because as you say you would go crazy daily going inside with mini screwdrivers adjusting the gear each time to get optimum bias etc… due to your varying voltage from the house.. This is why killing the issue off at the front right from the outlet and leaving the gear at the factory set adjustment would be best. Anyway I have made a decision and purchase..

Balanced / isolation transformer… It will have about a 5% loss bringing my wild voltage down to about 122, and in theory in turn give me 61 volts per phase on the output plenty low enough now being split into a balanced load for any gear to run much more optimally for the most part. Nothing fancy, nothing current limiting or adjustable just one continous clean output more or less regardless what the wall is doing, each leg will not vary much more than between 58 to 64 volts lets say which is not gonna be any kinda real shocker vs. how much difference there seems to be when running straight AC at 115 vs. nearly 130! Big difference in audio and video in my opinion.

By the way hi grade test equipment for accuracy and hospital gear and instruments are of course very sensitive much like your audio gear and for best consistent performance trust me they DON'T trust the Power company to get them 110 to 115 volts all day! They take many steps and pieces of power gear to make sure this is done internally.

Thanks for the suggestions.         
As far as iso vs balanced...

http://mysite.verizon.net/vze22yzp/id10.html

There are regulated transformers such as Sola (MCR series), Stabiline and Powerware (50Hz) that will correct (95V to 130V) but I doubt you'll want to be in the same room.
Undertow,

128V is pretty high. You must go through a lot of burned out light bulbs.

Are you sure the volt meter you are using is giving you a correct reading of the voltage? Is the meter displaying true RMS or peak?

I am looking to keep the system self contained and moveable vs. hardwired built in. I will have to take advantage of existing circuits for the time being. it
Undertow 06-02-09:

You still could get by using one main isolation transformer and a small panel. Especially if your main electrical panel is in a basement and is exposed and easy to connect to.

Of course you will need to hire an electrician to do the job.

Install the transformer and new panel close to the existing panel. The electrician can easily move the existing audio branch circuits to the new panel.

I would suggest buying a transformer with a 240V primary and 120V secondary. You may have to get one with a 120/240V secondary and just parallel the two secondary windings, 120V out.

Here is the kicker though... You will need one more smaller transformer. This transformer will be a buck transformer connected between your main electrical panel and the primary winding of the main iso transformer. The buck transformer, (configured as an autotransformer), will lower your now 256V mains down to 240V.

Balanced / isolation transformer… It will have about a 5% loss bringing my wild voltage down to about 122, and in theory in turn give me 61 volts per phase on the output plenty low enough now being split into a balanced load for any gear to run much more optimally for the most part. Nothing fancy, nothing current limiting or adjustable just one continous clean output more or less regardless what the wall is doing, each leg will not vary much more than between 58 to 64 volts.........
5% loss? Please explain the 5% loss.

NEC 2005 Code Article 647. Same for 2008.
http://www.equitech.com/support/647.html

Note, the neutral is connected to ground. The 120V out for power use is two ungrounded hot conductors.
.
Jea48, I purchased a Balanced transformer that will be 60 - 60 v out… The 5% loss is supposedly just from going thru the transformer, it is a 1000 va size, and I am told by the manufacture there will be about a 5% loss in voltage essentially giving you a slight step down in the process.

AS for light bulbs I have been using the ergo style flourescent newer curly Q looking type with no issue, but they have their own balast circuit built into the base which is why I think they cost more so this is probably why they don't burn the element as they are stepped way down from that internal ballast anyway unlike a cheapy 50 cent incandescent bulb.
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.
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 phases… 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.
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 phases…
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.
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.
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.
...although on the high side, 128V is within the ± 10% utility company voltage tolerance in North America. The voltage at my house has always varied between 121.0V and 124.5V depending on the time of day.
06-02-09: Gbart

Gbart,

Power utility companies are regulated by the State. My understanding is that most States require a + or - 5% for residential customers. 120V being the nominal voltage.
114V on the low side and 126V on the high side. Voltages are average not peak.

Here are a couple of Links for example. But as I said it really depends on the State one lives in.
http://ase.org/content/article/detail/2291

http://www.cmpco.com/UsageAndSafety/electricalsafety/powerquality.html
Jim
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.
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.
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.
I posted a similar question about 6 months ago on Audiogon, in reference to a high voltage problem I have at my location. I have been using an older tube amp that was not designed to run on higher voltages, and my lines are giving me a pretty consistent 124 volts. The voltages inside my amp run beyond the ratings on power supply caps. and other components, which can cause premature failures.
I needed to reduce my line voltage in order to extend the life of the amp, and tried a variac as the first affordable solution. I tried a good quality 10 amp unit, but unfortunately, it degraded the sound. I did not have the budget for some of the more expensive $1000+ line conditioners that could also regulate voltage, so I tried the following suggestion I had from a fellow Audiogon member: http://www.geocities.com/jonrisch/catch2.htm
It is a D.I.Y. high current transformer that can reduce output voltage AND be configured to output balanced power as well. It is a Signal DU-2 transformer, which can be purchased new for a bit over $300. I got mine on the used market for under $100 (E-Bay). I made my own enclosure for it, and wired it with a high quality AC outlet and power cord to the wall. I am now getting a constant 113 Volts for my tube amp, with the benefits of cleaner, balanced power. It works like a charm, and throws off very little heat and no hum. After re-biasing my tube amp for the lower voltage it puts out, it sounds fantastic with no loss of dynamics, and with a slightly deeper and more detailed soundstage. My amp runs cooler and all the new power supply caps, signal caps and other components installed from a recent re-build should last for decades.... Problem solved, and for well under $150!
Bigshutterbug, I believe it! As I stated above most audio gear regardless of its "designed voltaged range" will perform better the closer you get it to 110 volt side of things opposed to the high 120 and above in my experience.. Some don't understand it, or don't want to believe it, but it does work. By the way what is the exact make and model of the transformer you purchased? Do you have a diagram to configure it to lower voltage and balanced operation? I have seen the website and this project you refer too, I saw it was from like 1999, not that the year makes a difference, but anyway what size is the transformer? 500 va, 1000 va? Thanks

And again remember this kinda very specific and really major foundation stuff of an audio system in most peoples minds that get done last!! Room acoustics, and the power feeding your system is totally overlooked and probably accounts for 75% better results than a 1000 dollar preamp to a 10,000 dollar preamp.
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...
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
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.