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One more time: autoformers?

Not sure if this OP belongs in cables, speakers, or amps. Since I listed cables first -- it's cables. There are already some old threads which touch on the use of autoformers. Seems like most of the threads come up in the context of OTL and SET amps.

My Qs are: What are benefits and downsides to using autoformers? How does one know if an autoformer would be a good match for his/her rig?

As with most things in life, I suspect that autoformers must have downsides. Otherwise, everyone would use them. Open and intellectually honest responses are welcome.

Thanks?
bifwynne

Showing 2 responses by clio09

clio09
3,372 posts
 
If you haven't already check out the Paul Speltz Zero page where he discusses the benefits of using autoformers between the amp and speakers. I used a set we built between my OTL and planars to increase the impedance of the speaker which allowed my amp to drive them a bit better. My amp puts out more power as the speaker impedance increases so this was a benefit, but not all amps do this. I didn't notice any downside using the autoformer. I suspect with other types of amps what the autoformer does is affect damping factor and provide better amp/speaker matching.
clio09
3,372 posts
 
The Atma-Sphere amp I own will put out more power into higher impedances up to a certain point, which I believe is 32 ohms. After that point the power will drop. So you really need to know the impedance peaks of the speaker and where they occur as opposed to the nominal impedance.

Music Reference amps are designed for light loading. For example, the RM-10 I own will exhibit lower distortion and provide other benefits if you use the 4 ohm tap on an 8 ohm nominal speaker. The trade off is about 10 watts of power. I am not certain that this applies to all amplifier designs.

BTW - Some McIntosh solid state amps used autoformers and among the McIntosh crowd these amps are quite desirable.
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