MAC Autoformers?

Ralph,
I did read your white paper before entering this discussion. Lets just agree to disagree. Peter Walker designed the 57 to be used with an amplifier with a damping of 20 and even specified the series inductance. To say that these speakers will play with a damping factor of 1 is not fair to the speaker, no matter that some people like a widely altered frequency response. How can we discuss little differences in distortion when the frequency response has been so altered to make the speaker unreconizable?

Thats a nice little list of expensive speakers that represent a vanishingly small part of the market. I agree a single driver speaker like the Lowther will work just fine with your amplifier. 

As an antique radio collector I have given a lot of thought to how early SE amps (the 45 in particular) got relatively flat response without feedback. In that case the driver was a single cone in an open baffle cabinet so the impedance rise was not so severe and relatively flat. These early radios sound pretty good. However that does not represent modern popular speakers. 

ramtubes
Ralph,
I did read your white paper before entering this discussion. Lets just agree to disagree. Peter Walker designed the 57 to be used with an amplifier with a damping of 20 and even specified the series inductance. To say that these speakers will play with a damping factor of 1 is not fair to the speaker, no matter that some people like a widely altered frequency response. How can we discuss little differences in distortion when the frequency response has been so altered to make the speaker unreconizable?

Hear hear, good to see someone else thinks the same, about amps becoming tone controls with wild speaker impedance curves. Low output impedance (damping factor) and current are the only fix to make the amp stay reasonably flat.
Or I suppose you could have an "inverse tone control" to counter it, but the amp in question will start to gag itself very early in volume level.

Cheers George

I have started a new topic to explain how conventional output transformers differ from Autoformers.

https://forum.audiogon.com/discussions/autoformers-the-benefits-in-matching-amp-to-speaker

I also would like to note that the OP of this thread, Paul R owned a RM-9 Special Edition. We miss Paul, a really good guy.

I did read your white paper before entering this discussion. Lets just agree to disagree. Peter Walker designed the 57 to be used with an amplifier with a damping of 20 and even specified the series inductance. To say that these speakers will play with a damping factor of 1 is not fair to the speaker, no matter that some people like a widely altered frequency response. How can we discuss little differences in distortion when the frequency response has been so altered to make the speaker unreconizable?

You may not remember one of your customers, Bill Toberman (RIP, lived a few miles from me), but he had a set of RM-9s which beat out any ARC introduced to his system. He had Quad ESL63s. At the time I didn't think our amps would work with ESLs, but when Bill convinced me to bring them to his house, I was proven wrong- the MA-1s and Quads proved to be a match made in heaven. No loss of highs either, and this in direct comparison to the RM-9. The ESL57 proved even easier to drive and more accessible, since one of my employees had a set. In a nutshell, the FR is not as unrecognizable as you suggest!

We've also gotten Best Sound at Show using our amps with ESLs... all I'm saying here is there is more to this than meets the eye at first blush.

As we all know, there is theory, but there is also practice and we have many happy Quad customers. The thing is, OTLs can provide far more current than most people realize; I've seen one of our 12-tube output sections take out a 15 amp fuse...

As an antique radio collector I have given a lot of thought to how early SE amps (the 45 in particular) got relatively flat response without feedback. In that case the driver was a single cone in an open baffle cabinet so the impedance rise was not so severe and relatively flat. These early radios sound pretty good. However that does not represent modern popular speakers. 

If you recall the old days, speakers like Altec, Klipsch, JBL and others had level controls for the midrange and tweeter. These controls were not for room adjustment, they were there because the amplifier to be used had an unknown voltage response. **That** was how frequency response was handled in the old days prior to the introduction of the Voltage Paradigm. This practice persisted into the early 1970s as the industry switched over; KLH had level controls for their tweeters as did the AR-1, the world's first acoustic suspension loudspeaker. Of course, now open baffle speakers are back- one of them is in that list I posted above and its not the only one by any means. Google:
https://www.google.com/search?q=open+baffle+speakers&client=ubuntu&hs=UEV&channel=fs&...


Nowadays there are entire generations of audiophiles that grew up thinking that the voltage rules are the only game in town. In mid fi, that's certainly true but in high end the power rules have been in play for decades. That is why SETs are around. We've been making zero feedback OTLs now for over 42 years. The reason all this is going on is due to objectionable distortions-  and what kinds the ear doesn't care about. That latter statement is why the tubes/transistor thing has been raging on and on, and is why tubes are still in production (horns too), 60 years on after being declared 'obsolete'...


Just to be clear, we've been working on our own take on a class D amp for the last 2 years; not using anyone's modules, since we realized we had something to bring to the table. That amplifier acts as a voltage source; please don't think that I don't understand what's going on here. The paper was written because many people ask why we don't use feedback, and an explanation was needed that went beyond 'we don't like it'.


The reason 'paradigm' is used is because someone inside the paradigm (which is a platform of thought) will regard that which is outside the paradigm as blasphemy or heresy- it can't possibly be right. But this is history: the Power Paradigm used to be how everyone did it. These days our understanding of physiology has greatly expanded so we can better see why there can be a benefit to this approach.  

ramtubes
I also would like to note that the OP of this thread, Paul R owned a RM-9 Special Edition. We miss Paul, a really good guy.

Totally, "top bloke" had many late night discussions with him.
He really loved his RM-9 Special Edition which he said was a perfect match with my "Lightspeed Attenuator" which he also started thread on, which exploded to over 18 million hits, made my life hell and interesting at the same time, rip Paul miss you heaps.

Cheers George