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
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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.