One more time: autoformers?

Well, as far as I know, OTLs are the only amp design that increases power into higher impedance. Though many amps may struggle when impedance dips too low (not sure if autoformers help this or not).

Amps certainly can push power into 40 or 60 ohms. These are not unusual impedance values for headphones (and some headphones have much higher impedance values). But a SS amp and a tube amp with transformer and speaker taps for 4,8,16 ohms would be putting out considerably less power into these impedences.

That's about as much as I can help here (if this could be called help).

+1 on reading Speltz's webpage.

Thanks Roscoe. There's a number of "EE" type members who I hope chime in too.

No +1 point for reading the Atmasphere white paper too??

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.

Thanks again Clio. I recall reading somewhere that certain Atmasphere amps had a 32 ohm ceiling. I tried the 4 ohm tap. The music su*cks. Went back to the 8 ohm tap.

Btw, been using my sub-woofer a bit more aggressively than before, i.e., raised the gain a little and raised the cut-off frequency to about 80 Hz. Going by ear, I think the sound stage opened up quite a bit. I don't know why. Maybe my finished basement is a giant bass (or is it base? - LOL) trap.

I'm speaking from experience and don't really care about theory or numbers. My Atmasphere MA-1's were not doing a good job of controlling the lower frequencies of my Aerial 10t's. They sound flabby. With autoformers the bass dramatically thighten up and allowed for a more linear presentation without a loss of sound stage. I already owned the 10t's when I bought the Atmasphere amp and preamp so I had to do something to solve the mismatch. In my case it worked very well but I must add the cavet that I'm in the process of setting but my brand new Merlins which should be a much better match to the OTL's. Autoformers are only suitable for certain very specific situations. If all works well with the Merlin's my autoformers will be for sale as the 10t's are headed for the Man Cave and will be driven by a Bryston amp. No autoformers necessary.