Using autotransformers

The term 'autotransformer' is a new one on me, and I have been a technician and engineer since 1974. I suspect that you mean something else. Which of the two below seem like what you are looking for?

An autoformer has no ability to regulate voltage. It can change the voltage, that is all.

If you want to adjust the line voltage, a variac can do that.

Perhaps Puerto is referring to something like this, which is essentially a motor-driven variac/variable autoformer/variable autotransformer, with a control circuit that causes the output voltage to be automatically readjusted whenever it deviates from some nominal value by more than a small amount.

I have used one in the past for non-audio purposes. During times when the motor runs, it makes way too much noise for it to be positioned within earshot of the listening room.

I have no idea what its effects on the sonic performance of an amplifier would be, if any. But I would imagine that whatever effects it might have would vary depending on the design of the specific amplifier.

Regards,
-- Al

Puerto, exactly what kind of incoming voltage "irregularities" do you have ?

It has been suggested to me that the best way to avoid incoming voltage irregularities from the street to my Krell mono blocks is to add an autotransformer to each amp's dedicated 20 amp line.
Puerto

Buck / Boost transformers can be configured as autotransformers.

If you have a constant low voltage you can Boost the voltage to a higher voltage.

If you have a fairly constant high voltage you can Buck, lower, the voltage.

Autotransformers do not have any regulation or isolation properties.

http://www.toddsystems.com/geninfo.html

http://en.wikipedia.org/wiki/Autotransformer

http://www.writenowcommunication.com/PDF_Files/Apps/App11.pdf

http://www.acmepowerdist.com/pdf/Page_104-109.pdf
.

Al, we use such a device in our MA-3 amplifier http://www.atma-sphere.com/Products/#MA-3

Otherwise the amp would draw the line voltage down in a lot of situations and not make full power.

Depending on the power requirements you might be able to use an automated variac, but IME what is needed is an additional isolation style transformer that is much larger, and the automatic variac is used to buck the line voltage to it. This allows you to use a smaller variac and control a much larger amount of power that might be needed in a larger amplifier.

When I referred to voltage irregularities I was talking about constant variances in the incoming voltage. Often as high as 130-135 Volts and on other occasions it would drop to below 110. Already I have spent big bucks on the repair of a Krell FPB 350 because the caps overheated and leaked all over the circuitry.

Just got back into town so will review the comments above and respond. Don't go away!

I have read (and re-read) all of your posts - Thank you! Yes, Al, you were right. I was considering an autotransformer as defined in Wikpedia. The idea was not mine but someone who works on all forms of electronics. Now I am wondering if looking for something that would control the entire house might not be a better choice. We currently have voltage regulators on most large appliances, including the APC battery back-up but nothing on the amps.

All of the options look expensive, OTOH, paying 1,000 to repair an amp is not cheap either.

I will look harder at the Variac and see if that makes sense.

Thanks to each of you for the input.

Often as high as 130-135 Volts and on other occasions it would drop to below 110.
04-28-13: Puerto

Your profile says you live in the USA.

If you live in the USA contact your power company. Power companies here in the US are regulated by the state. Most if not all require a max voltage variation of + or - 5% average, RMS.
120V being the base line. + 5%) 126V - 5%) 114V.

Now if you are experiencing low voltage at times in some parts of the house and high voltage in other parts of the house at the same time that is a horse of a different colour.
That usually indicates a loose service entrance neutral conductor.

I do not live in the USA. I now live in Mexico.

I do not live in the USA. I now live in Mexico.
04-29-13: Puerto

Puerto,

You do have a few options.

* Sell the Krell mono blocks and buy amps with auto input voltage sensing.

* Install a Constant Voltage Transformer, CVT. Also known as a Ferroresonant transformer.

* Buy an Automatic Voltage Stabiliser, AVS.
Example of, http://www.monstercable.com/productdisplay.asp?pin=2137
.

Ferro-resonant transformers don't work so well for audio. They make a lot of physical noise and electronic noise too.

The AVS looks interesting. I can contact them for more info but do you know, of hand, if the AVS would handle the load for 2 Krell Monos or would you have to buy an AVS for each amp?

Hard to say. Monster's website seems pretty bad, and does not say how much current the device can handle. You will have to call a dealer or such and find out.