MAC Autoformers?

Saying that autoformers are a fix for a flawed amplifier design as Stanwal said is in my view just ignorant.

I don’t think Stanwal meant that, they didn’t purposely go out and design a flawed amp.

I believe he meant that with an autoformer an amp can be designed with lax’ed parameters eg: that make it stable. And that an autoformer can then isolate it from the bad outside world speaker emf etc, that may make it go into oscillation or ring or whatever. This this autoformer makes this amp listenable and reliable. It's a Band-aid.

But if the amp had great design in the first place as not to have any lax’ed performance issues, the an autoformer is definitely a backwards step regarding sound quality.

Cheers George

George,
You are still saying that it's a Band-aid, and I disagree.

 I’ll hazard a guess that Mac chose to use autoformers way back when early transistors weren’t as reliable. They chose to use the autoformers to increase reliability (which way back was part of Mac’s separation from much of the competition) and because it fit in with design parameters that they were already comfortable with. Most speakers of that era were thought to be used with tubes by the end user, that might not have realized the compromises that the autoformers introduced. IMHO, there is no good reason to use autoformers with the rugged transistors that have been available for almost 5 decades since then.

Ralph wrote:

"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!"

Based on past posts with Ralph and Al (Almarg), I get Ralph's point.  As I mentioned above, my ARC Ref 150SE uses about 14 db of negative feedback and has "low'ish" output impedances off the 4 ohm taps (about .5 ohms or thereabouts ) and the 8 ohm taps (about 1 ohm or so).  But even still, I can hear a discernable difference in tonality when I play my speakers off each set of tabs because the speakers do not have a flat input impedance function over their frequency ranges.  So much for a flat speaker output frequency response, ... even if that was really ever possible with a pure voltage paradigm amp.  And that doesn't even touch on TIM distortion caused by using negative feedback.  

For pure tube enthusiasts, the only solution is to find speakers that have flat and high'ish impedance functions (say 16 ohms) over their entire frequency ranges.  I do not think there are a lot of beasts like that out there.  Ralph, if you can make some suggestions, please do.   

Btw, another knotty subject that Ralph and Al have posted about some years ago is low damping factor with high output impedance tube amps.  Ralph, I forgot what you posted.  Care to re-educate us?

Thanks.

BIF

unsound
I’ll hazard a guess that Mac chose to use autoformers way back when early transistors weren’t as reliable. They chose to use the autoformers to increase reliability (which way back was part of Mac’s separation from much of the competition) and because it fit in with design parameters that they were already comfortable with. Most speakers of that era were thought to be used with tubes by the end user, that might not have realized the compromises that the autoformers introduced. IMHO, there is no good reason to use autoformers with the rugged transistors that have been available for almost 5 decades since then.

Yes this is well pointed out by unsound, they continued today because of a market niche they made for themselves back then with the "new questionable semiconductors" of the time. They continued with it even though it’s not with today’s semiconductors, and has become the opposite, a compromise rather than an aid.
Or roxy54, a band-aid fix for poorly designed amps that can’t drive certain speakers. In this case your better off with the right amp.

Cheers George