MAC Autoformers?

The autoformers restricts the ability to vary power with impedance / sensitivity and ergo compromises frequency linearity with the vast majority of loudspeakers.
There’s a good reason so many other amps don’t use them.

Why hinder the performance of a well designed solid state amp with an autoformer, unless it was a bad designed one to start with.
A simple test is to put a well known Auto Former that’s used on OLT’s to make them "sort of work" into speakers they can't drive without them, on the rear end of good solid state amp (say a Pass Labs) and watch it transform into rubbish.

Autoformers are "band-aid fixes" for amps that are not right before them to be able to drive into loads they shouldn’t be on without them. Get the right amp to start with, don’t just put a band-aid on.

This statement is false. Most solid state amps will sound better when driving a higher impedance load as they make less distortion. This is easily seen in the specs.

The autoformers restricts the ability to vary power with impedance / sensitivity and ergo compromises frequency linearity with the vast majority of loudspeakers.
There’s a good reason so many other amps don’t use them.

This statement is false as well. The use of an autoformer or full on output transformer does not prevent an amplifier from acting as a voltage source.

Mac built tube amps in the 1950s that behaved as voltage sources (and just so we're clear, a voltage source will put out the same voltage into all impedances the speaker presents, which is what any good solid state amp will do) and many tube amps with output transformers act as proper voltage sources. In fact Mac lead the way in the 1950s and 1960s (along with ElectroVoice) in getting the idea going that a loudspeaker should be driven by a voltage source. To suggest that somehow 60 years later their ideas suddenly no longer work is ludicrous. 

Personally I don't think that having an amplifier that behaves as a voltage source is the most neutral way to go because the factor that is left out here is the function of loop negative feedback, which is used in the vast majority of amplifiers. But it is this design aspect that allows amps with output transformers to behave as a voltage source- add enough feedback and almost any amplifier will! I don't like feedback as it adds distortion of its own, but if you are going to take the position that an amplifier won't act like a voltage source (which is exactly what is posed in both quotes above), then you'll have to deal with the facts which are in contradiction to that position.

"A simple test is to put a well known Auto Former that’s used on OLT’s to make them "sort of work" into speakers they can't drive without them, on the rear end of good solid state amp (say a Pass Labs) and watch it transform into rubbish."

georgehifi,
Did you perform this test?

+1 Good question roxy54,  my guess is of course not......geez.....

roxy54
Did you perform this test?

Yes I had a customer trade a pair in, he tried them on his Lamm 1.1’s and didn’t like them, I put them on my very good solid state amps with my ML ESL speakers to see what they did, and it made them sound like old an Williamson tube amp soft polite and rounded. As I said the same years ago in Audiogon.

Mac did build good amps, they were the 275's, should never have gone to ss with transformers. 

Cheers George

my guess is of course not......geez.....

Really!!!