Using a shore power isolation transformer at home?

Do not forget that you will pay for energizing the coils of the transformer and it can cost more when your equipment is off than on. I tried this and it was not cost effective IMO, 4 amp input draw at static with no output load. I put it on the back burner for now till I can figure out how to put it on a starter without tripping the breaker 20% of the time. Fuses may work I just have not the time to try it yet.

Mrtennis,

It is hard to know remotely, but wrong volage is probably the easiest thing to detect, just measure it. If it is indeed too low, might be possible to demand your power company to fix it.

ultimately, the amplifier needs sufficient current to do its job and the ac needs to free of noise. if voltage gets to low, some amps will have a problem. within a range, the actual voltage probably doesn't matter.

is it noise pollution or low or high voltage that causes changes in frequency response during the summer months ?

Face,

Isolation transformer is to address the input transformer vibration that is caused by something in the AC. Fluctuations are to be addressed by that servo-regulated variac. Sorry, I brought another topic under the same thread.

I don't understand how an isolation transformer would help with voltage fluctuations.

Oil change every 10,000 kWh, as usual :)

Seriously, mechanical? How Victorian. A modern classic. Hope you like cleaning and replacing brushes. Do you have to grease it or just refill the whale oil?

Sorry, I forgot to tell what Monsters AVS 2000. Here is a photo: http://www.bukutronics.com/?p=54. Besides those "high voltage suppressor" and "radio frequency suppressor" (see here) which I will surely bypass before I use a unit, this is nothing but a variable transformer (variac) with a motor that rotates its pickup contact, trying to keep sharp 120V.

The Monster bastards charge for a new unit 4-5 times more than what it is worth; besides, they almost surely limit the current by their "suppressors". However, to buy such a unit for under $500 (btw, the variac is 3 kW rated) and to slightly mod it into something less limiting starts making sense, at least to me. Of course, this type of a device does not give an instantaneous voltage correction if something serious happens to the AC line (that is why I want a non-limiting surge suppressor from PS Audio after the variac), but what I have most of the time in my place is a "slow floating" somewhere between 118..225, which is driving me nuts! To give you an example: those fluctuations are wide enough to cause the filaments on my 45's to go all the way from the allowed minimum of 2.45 to the allowed maximum of 2.55. Wouldn't you find that annoying?

What you are saying about transformer vibration is right, let me tell you what I have narrowed it down to. Two important things: first, it happens relatively rarely, and usually at nights. Second, similar thing start happening to other electrical devices - at least, to the ones connected to the same AC line from the panel. What I have not done, unfortunately, was to check whether other AC lines from our panel suffer from this also - probably, will do it as soon as this humming happens again (btw, the hum is rare but very obvious, nothing to blind-test here). To conclude, what I know for sure is that the transformer vibration is caused by something that occasionally comes from the AC; what I do not know yet is whether the cause is inside our house or something outside.

There are other methods of regulation but "servo" just means some kind of feedback and not sure what that means here. A household thermostat can be called a servo.

And not all tap switching implies a stepped sine wave, if it's done at half cycle.

http://www.contractorsav.com/article/2006/11/07/ac-power

I point out this article with the caveat of who it's written by, what they sell, and when it was written. It's sincere but an obvious bias in the tone.

In the regulation section, the last type is also known as "tap switching" and they have limits too. Also doesn't mention reaction speed and the resulting stepped sine wave.

Regenerators have gotten more efficient with SMPS but they're still expensive.

Tried a ferro-resonant 1000W Sola MCR that I got off Ebay for $20 (3% regulation along with substantial noise reduction) for the TV and they are noisy. Sola HD has an interesting online FAQ section that's informational.

Not entirely clear why you think you need regulation. Within specs required. Seen a lot worse.

Transformer vibration can be from any number of reasons, from a loose bolt to DC offset (caused internally to your house or external) or a defective transformer. Would like to narrow down the problem before throwing too much money at it. Maybe take it to a technician. Try a PS Audio Humbuster I think they have a trial period ;)

BTW, an isolation transformer will not pass DC to the component transformer but that also means that the problem MIGHT just get relocated.

throw away, I mean :)

Just looked at this diagram from Monsters of their AVS 2000.

Probably, I will through away all pre-transformer filters, to make it even less intrusive.

Voltage is unstable, and I want 120V sharp. Isn't a servo stabilizer the way to do that in a non-limiting, neutral fashion?

Why not?

Except for the dedicated lines, not really.

Thanks, that was very detailed!

I am planning to install a dedicated line, and I am comparing the possibilities. Right now I have two main issues with power:
(1) sometimes the power transformer of my amp hums much louder than it should, and some "fraction" of this noise even penetrates into the speakers;
(2) the AC voltage can be anything from 118 to 124.

The former I hope to cure with a dedicated line (probably w/o any isolated transformer to start with).

The latter (which probably does not affect the sounding too much, but drives me crazy when I want to set the optimal regime for the tubes in my amp) I plan to cure with Monster's AVS 2000 variac+servo (I am almost ashamed to use anything from those bastards, but it looks like these servo-stabilizers are their only product that does what it says and is priced adequately, if buying used).

To have a layer of protection just in case AVS 2000 goes crazy, I plan to put PS Audio's Duet between it and my tube amp.

Does this all make any sense?

Just attach both grounds together with the shield wire, if it has one. In the case where primary and secondary are on opposite sides of a transformer, both grounds screw down to the casing on either side. If it's metal encapsulated, that should be attached to ground as well. Continuous ground.

Ground and neutral are not, technically, the same. That's why they are different wires.

1) If you're using a 480/240-240/120 step-down transformer, such as the encapsulated Acme or Hevi-Duty, you must use 240V in. Cheap on Ebay - industrial recyclers. Can be more expensive for shipping.

Topaz/ Xentech/ Phoenix are available in 240/120 and 120/120V models. The former can be used with either voltage in. Surplus distributors, Ebay occasionally. More expensive than general purpose, industrial step-downs.

If you have dedicated circuits and you're hard wiring, 240V has some minor advantages. However, minimum code in many areas for 240V wiring is 12/3 with a 20A rating (12 gauge, 2 insulated hot, 1 insulated neutral, 1 naked ground which is not counted as a conductor. That's even if the neutral isn't utilized). If you're splitting that up before the transformer, that can lead to phase issues. If you already have dedicated lines, chances are they're 12/2 and not suitable for 240V. Locating the transformer near the distribution panel solves that issue as well as mechanical hum, if the panel is in an unoccupied area.

For either type, the maximum draw (aside from momentary start-up spikes) must not exceed 80% of the transformer rating. For audio, I prefer closer to 50%.

2) Usually a bad idea. Been discussed a few times on these forums. Even if they're bonded together, which is a must, there might be issues if they are not in close proximity. An additional ground rod for assurance, within a foot away from the original, should be fine, if you know what else is buried there. Of course, I'm just guessing. I'm not an electrician but I stayed at a Holiday Inn last night.

Ngjockey, thanks!

Can you please clarify what do you exactly mean by "grounded input"? Shortening the neutral THAT COMES FROM THE PANEL TO THE TRANSFORMER to ground? Why is that a good idea? I've never heard of doing that (I am not very experienced with "pre-receptacle" wiring and might be wrong here: when you take something right from the panel, you can, probably, assume that ground and neutral are, essentially, the same).

Let me ask two more questions:
First, is it a better idea to have 2:1 transformer, converting 240 to 120?
Second, is it a good idea to add "enhanced grounding" via some buried rod?

Thanks!

I've looked at them a couple times but have never purchased. Remember one brand that advertised a 3.6 KVA unit at nearly half the weight of their 3.8. Never been quite sure if they are shielded (more noise rejection) and the plastic enclosure would retain more heat, although not significantly compared to a potted unit. More importantly, they've always been more expensive.

Transformers must be grounded continuously. Input, output and shield to chasis. Usually center-tapped secondaries to ground in balanced configuration as well.

Thanks!

Ultra/extreme isolation transformers are built to specifically reject high frequencies (noise) from passing through too.

Why are they not the same, from the electrical point of view?

They really aren't the same thing exactly, but it might help, just to a (much) lesser extent.