MAC Autoformers?

For us non Mac enthusiasts the autoformer has always been proof positive that Mac had no idea how to design a transistor amp, perhaps they are coming to their senses at last.

I'm not even sure what the autoformer does. It seems like an effort to provide the same level of power no matter what the impedance load of the speaker is - which in theory sounds like a good thing. But I don't understand much of this. I did not know there was controversy regarding autoformers - so I wait to be enlightened in the issue here.

I agree with Stan. I just wrote this a few minutes ago:
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1262654269&read&3&zzlNolitan&&

Mac's autoformers kills the amps transparency characteristics.
Also some used to refer to them as having poor transient response(the autoformer). That was a big edge companies like Accuphase had over Mac transistor amps years back,plus other companies now.

I'm not nearly as knowledgable as our "in-house" expert, Aball, on all things McIntosh, but I do know that my MC7200 does not have the autoformers and it is one very nice sounding amp, probably one of the best McIntosh built for the money. As usual, opinions will vary...

I am not a Mc fan, nor am I a proponent of auto-formers such as speltz's, but I wouldn't be so quick to shun them or their use by Mc. Transformers are a mature technology that modern audio has only begun to tap (pun intended), ie- amorphous (metallic glass) cores are seldom used. One reason comes to mind, transistors typically don't have the same transfer characteristics between P and N types (PNP/NPN) and transformers allow use of one type for push pull operation. For me the "whole" is far more important than the parts.

go with a model with autoformers.

The MC7200 is one of the finest amps ever made by McIntosh BECAUSE it does not have autoformers (another being the MC122 - no meters though, 80w).

You have to admit this is confusing. Now it seems that Mac uses the autoformers in the "higher end" units. Why would the do that if it hurt performance? I can't imagine they don't have technical competence and the autoformer is some kind of bandaid for inferior SS design chops. Aball, where are you?

I would guess that that a Mac with autoformer will sound good => better => best depending on the speaker load. A very demanding speaker load, the autoformer will be of a benefit, therefore, in theory, better sounding. A speaker with a very benign load will sound better when used with a non-autoformer amplifier due to the simpler topology. Or, you can listen to both amplifiers and pick the one that sounds the best to your ears, but that makes for a very poor forum discussion.

If it gives such great benefit why don't other companies use them? It is quite true that transformers are a mature technology so if they gave an improvement in this area it should have been seized on by many of the "cost no object" amplifier designers. Krell , for example, will drive very low impedance loads at least as well as the Mac without transformers. The question here is whether their prime purpose is to improve the sound or protect the amplifier. Since the transformer is the prime weakness of tube designs it is hard to see how it will help SS ones.

I think that the McIntosh autoformer is utilized for a number of reasons. I have had a few amps with and a few without. The ones with sound better than those without, IMO. The cost, weight and size of the autoformer is probably the main reason McIntosh doesn't use them in certain amps. I have found that the non-autoformer amps lose detail and that "tube warmth" and seem to have a brighter less musical presentation, again IMO. The question as to why other manufactures don't use autoformers is probably due to them not wanting to add the circuitry to the output stage. But keep in mind that McIntosh designs their amps knowing they will use it and design with it always in the grand scheme. The non- Autoformer amps have a totally different topography it is not like they just add it to some and not others. I am quite sure that McIntosh realizes that the autoformer causes a level of diminished performance by it's employment. But I think in the overall scheme of things McIntosh builds their products with a few goals: Sound Quality, Product reliability, protection of circuitry and speakers. Maybe they are willing to sacrafice some sound performance to acheive a "built like a tank" amplifier that will provide years of reliable service, and let me add here, that this is my theory not fact. I have bought as mentioned many McIntosh amps and preamps. The one constant in all of these is they always work and they always sell quick and hold the majority of my investment.
McIntosh is not for everyone, but then neither is Chevrolet, Levis, or asparagus. Pubul57, my advice is buy the Mc amp with autoformers. You will receive maximum McIntosh performance and maximum resell when you move on.
If you want the best amp ever made, then spend the rest of your life reading the opinions of audio enthusiasts, myself included, among those found in many many forums. But in the end make your decision must based on 2 things 1)what you hear and 2)what you can afford at the time. This is all of course my OPINION only and I could debate this for weeks on end with those who disagree. But this is what I feel and you must adhere to the 2 decision makers listed above. As a final note, in my years of buying audio equipment and reading forums I can think of no other brand that receives more bashing than McIntosh. I have dealer that bashes Mcintosh all the time but in his secret room it is all McIntosh, go figure. However, I see them holding the some of the best resale values. Do what makes you happiest and enjoy your music the most that you can.

I am pretty sure that MAC had or has a patent on the autoformer. It is expensive to manuf. I have had both.
I would not refrain from a MAC purchase because it did
or did not have them. They do put them in their more expensive equipment. The autoformer does keep that sweet MAC sound with all loads. MAC's without autoformers do not have problems with loads either.

I would not call them degrading.....I saw the ad the poster
was referring to.........it is an ad. I would not give the same opinion. I have sold a few amps that were more powerful to the ear and went back to MAC.

Oh Boy! This is an old argument, and when it pops up, you invariably hear someone say that Autoformers add distortion, decrease detail etc. It is all nonsense. The proof is in the sound, and the amps with Autoformers sound fuller and more effortless and authoritative (to me) than those without. Bottom line, the "Mac Sound" is best expressed in the amps with Autoformers, and it's a great sound, so if you are going to get a Mac amp, I would say get one with Autoformers.

Different circuit designs accommodate different components. To say any amp is good or bad based on the fact that it has either transformer or direct coupled outputs without listening is just a foolish generalization.

I have used many Mac amps over the years (since 1978) except for the latest models, whose prices are truly hideous! My conjecture is the same as ONTJESR, the 7200 was/is the best amp they've made, and with no autoformers.. In my experience, all the autofromer models had a "flabby, not tight" bass. The 7200's bass is deep and tight. I always thought what most of you express, if they're so great, why don't other manufacturers use them? Mac claims it lets them match the loads to any speaker impedance. I own the 7200, and have yet to hear the un-tube-like sound some of you claim to hear. This is their best amp I've heard! THEO says it about right!

The reason I though the autoformer was a good thing is that my speaker manufacturer (Merlin)suggested that if I want to add an SS am (I own two tube amps that I switch around)to consider the MacIntosh with the autoformers, which is interesting in light of some of what has been said here in that they have a very easy load and very smooth impedance curve, where the autoformer would seem to be less needed. Well I think I'm going to decide based ergonomics and not worry too much about the AF/non-AF issue. Any opinions on differences in sound quality, or other considerations between the 6300, 6500, and 6600. Power is not an issue, my speakers run perfectly fine on 50 watts or more.

I think the 6300 is a sleeper......It does use THERMAL TRAK
which keeps it running cool all day.....it does not have
BASS/TREBLE controls but the pre-amp section is great.

It uses LED's instead of bulbs.......I thought the 6500
was quote unquote "louder" but the 6300 sounded better to me.

I like balanced inputs my self which the 6300 has.
With MAC people do not talk enough how important your source (cd player, dvd player, server etc.) is relative to your sound. Do not get me wrong, I know it is on all equipment, but you can REALLY hear the differences
on MAC stuff. Only as good as what you plug into it.

All three are good pieces of equipment. Never understood why the 6600 has such a bad rap.

That is funny about the guy who always bashes Mcintosh and has it himself. I know someone similar. According to my friend, McIntosh cannot do anything right except in his own listening room. Go figure.

Hi all, After reading this discussion I just thought I'd mention that I've noticed on the used market McIntosh amps that have autoformers seem to go for more money than the ones without. I've seen some Mac amps from the 70's go for more money that ones with out autoformer that were made in the 80's and 90's. Also I have a Mac MC2105 and I think it sounds much better than the Adcom or the Belles amps that I had prior to it. And go figure, the Mac is close to 40 years old and still works like a charm.

My System:

McIntosh MC2105 Amp
McIntosh C504 Preamp
Sansui TU666 Tuner
California Audio Labs Alfa DAC
California Audio Labs Delta Transport
Micro Seiki DDX 1000 Turntable w/ Sumiko Premier MMT tonearm/Linn Asak MC cart.
Musical Fidelity X-LPS phono preamplifier
Vandersteen 2CE Speakers

Loving my MA 6600 with the AF's. My understanding autoformers give you full power at any impedance. That's a bad thing...I don't think so. And after some many decades I think MAC could employ there use without degradation. That other makers don't use them, cost and the thinking it is not necessary for their designs. But McIntosh has always tended to go the extra mile, and have the philosophy of "bonus built" components.

As for some of the differences in their integrated amp line up. Along with the very musical presentation some nice features, such as electronic tone controls and level matching. Secondary output to drive another amp. Led lighting among others makes for a very nice package in the MA 6600.

Had the 2105 and the 7270,havent heard Mac amps without them so cant compare.I can say both came close to Ayre,CJ,Counterpoint and a couple others.This would be with Merlins,YMMV,cheers,Bob

McIntosh is simply making some different design decisions in using autoformers. Comparing an autoformer amp to a Krell, for example, one notices a distinct difference in how they're rated. The Krell tries, and usually succeeds, in having the ability to output a consistent maximum voltage level regardless of the impedance of the load. Because the voltage limit is fixed the maximum output current varies. So the Krell puts out X volts into 8/4/2/1 ohms, and that might correspond to 300/600/1200/2400 watts, for example, depending on the load.

The autoformer amps have a different design goal, output a consistent maximum current regardless of the load's impedance, using the autoformer to "match" the load to the amp's output stage. So a McIntosh amp might be rated at 1200 watts into 8, 4, and 2 ohms.

Which is "better"? Well, that depends. Assuming your maximum listening levels cause a current draw well within the limits of the amplifiers, I can't believe there will be much of an audible difference in sound attributable to the autoformers. They don't add distortion, but they *can* affect the system's frequency response.

The autoformer adds some resistance in the output path, so the so-called damping factor, or the output impedance of the amplifier, is probably going to be a lot higher than a direct-coupled amp, like the Krell. It's all that wire in the autoformer; it adds resistance. How is this audible? It may not be, but if you have speakers that present a very low impedance load you could have a roll-off or dip at those frequencies where that happens, I suppose. Will the roll-off be audible? I don't know, but some speakers do present very low impedance at some frequencies (early Legacy Focus, Apogees, and Wilson Watts come to mind), so if you own one of those I'd stay away from autoformer amps, but that's not intended to be some deep pronouncement.

Autoformer designs allow a manufacturer to spend more on producing high current into higher impedance loads, so assuming there was some real relationship between cost and price (there really isn't for products like this) for X dollars you could get more watts into 8 ohms than with the non-autoformer design. Take a look at the MC1.2 for example. 1200 watts/ch into 8 ohms. What does Krell offer that puts out 1200 watts into 8 ohms, and how much does it cost? Of course, the MC1.2 will still put out 1200 watts into 4 ohms, while the Krell is putting out twice the watts into 4 ohms, but since the MC1.2 starts out so much higher in power, you don't really see the two design approaches differ until very low impedances, when even a low-end Krell amp is putting out over 2000 watts, assuming you have a 220v/30amp power line running to the silly thing.

So are autoformer amps better or worse than direct-coupled amps? For most speaker loads you'll never hear a difference, but I admit to strongly preferring the direct-coupled approach, assuming you can afford a good enough amp that it does indeed act like a good voltage source, like a Krell. I think a very low output impedance is indicative of a better design, but I wouldn't bet five cents on my ability to tell the difference in a double-blind test. It's just my opinion, but I'm the buyer so I get to have one that counts!

I don't own McIntosh, but for the last 10-15 years, their amplifiers have been excellent and increasingly desirable sonically. I am a SET tube amp listener, yet ironically I am most likely to become a McIntosh owner when I can find the money and space for a pair of MC1201 mono blocks or their MC1.2kw successors.

Philosophically, as someone who has built amps and as a listener, I am inclined toward direct coupled designs, but the proof is in the listening. Forget your topological biases and there will be no doubt that no existing direct coupled McIntosh solid state integrated amp equals the musicality, tone density and overall fidelity of the autoformer-based amplifiers above them in the line.

The 6300 and 6500 are certainly quite good for what they are, and well-made too. The autoformer 6600, 6900 and 7000 are as a group distinct step-ups in musical truth. The next step function boost in fidelity comes when the quad differential circuit is added to the mix, in the power amps from 402 and up. I'd love to see a 7000 add the quad-diff circuit.

Go have a listen and decide for yourself.

Phil

I noticed I made a grammatical error in my last post that could mislead people. Autoformers increase the output impedance of the amp relative to direct-coupled designs, which leads to a LOWER damping factor. My apologies for being such a lousy editor.

I wonder if you run a bunch of drivers , in series, which means higher impedance if the wattage stays constant... -with an auto former-

So let's say... Since I like to use DJ'ing as an excuse to buy audio gear for my home system.....(lived that lie since I was 17 in 1981) could I run several JBL Alinco magnet 18" subs in scoops in series and not continuously half the power as I run into higher impedance loads??? That to me is better than running low impedance loads and stressing the amps and generating tons of heat and a lower dampening factor.

I know there is no free lunch... but would I be better off running say... (8)18"
woofers (8 ohm each) in series parallel arrangement to give a 8 ohm load with a Mcintosh as opposed to running them in parallel for a 1 ohm load with a Krell?

Read what Mac's designer says. A push-pull amp has, by its nature a lower output impedehttps://yesonazsolar.com/nce in the bottom stage. The autoformer corrects this mixed-matched problem and matches the sometimes large fluctuations in total output impedance some the speaker always gets the same current no matter its impedance so it will not blow because of a demanding signal. It is BOTH a sonic and safety issue.

My 2 cents is after talking to Mctintosh Tech Teryy somebody in Knoxville TN, research,the verdict is that autoformer as opposed to direct is a different but very d=techniacal approach. Your own ear is the judge. Mu experience is with MC 2200 paired with Martin Logan motion 10 +sub. Results were very Impressive used 3 different venue's (rooms).

So my Net answer is I think due to dedication & quality, Mcintosh had a game winner.

 Very versatile  amp with rich smooth Mcintosh sound, attention to quality, is the defining difference but people forget how dedicated Frank WAS.
RobyK

other companys don't have autoformers because mcintosh has a patent on it!

If you read Ken Kessler's book, there's significant disagreement about Autoformers between the various designers.  I think it might've had marginally better relevance in the very early days of Solid State.  Now there are even CAR stereo amps that can run .5 ohms all day at negligible distortion.  It has to be a cakewalk for well isolated AC.

This is an old topic...literally.  In the times when tubes were dominant amplification devises, the output transformer was a necessity (one might say a necessary evil.  The tubes are amplifying voltage, so that they work with high impedance loads. The loudspeakers normally have quite low impedance. Thus a transformer is required to match the output of tube amplifier and the loudspeaker.  When first transistors have emerged, the schematic design did not evolve immediately. Thus, early transistor amplifiers were very similar to the matured at that time tube amplifiers. 

However, over time it was realized that transistors work better and amplifiers of  current as opposite for tubes which work better as amplifiers of voltage. Thus, transistor amplifiers can and do work well with low impedance load such as loadspeaker directly. 

Now, still transformer (autoformer) can assist with the loudspearkers with various impedance...i.e. 4 Ohm vs. 6 Ohm vs. 8 Ohm providing more stable load to a SS amplifier.  However, transformer alone is not a perfect transfer devise and making quality transformer for audio output is difficult and costs a lot of money. The typical issues with output transformers are: reduced damping factor and difficulties with driving complex loads, slew rate reduction, additional distortions, etc. 

From my perspective, McIntosh polished out the technology and because of the quality, manages to make very good sounding amps. The majority of other brands simply moved on ( which at this point seem to be the right thing to do) and still makes good amps. At the end of the day it is not the technology but the end result that matters.  

I have a C40 preamp driving an MC150. The C40 has an onboard 20 watt monitor amplifier. For low level listening in the evening, I use the monitor amplifier; for performance listening, I use the MC150. Both of these amps are wired into an "A-B" amplifier switch box that can instantaneously switch between both amps. On occasion, I have switched between the two trying to hear any differences. They both sound identical to me. 

I also have an MC754 driving some old JBL's for the TV. One of these days, I'll have to get of my lazy caboose and rewire to see if there's any difference between it and the MC150. I suspect there won't be much difference, if any, in the sound.

I've also demoed a pair of MC601's along side a new model MC275. Again, both amps sounded outstanding, but I heard no notable difference between the two. In that case, I'd go with the MC601's because they (a) have more power, (b) don't require tube maintenance and (c) have those lovely blue meters.

I personally prefer any McIntosh amp with an autoformer, but it's based purely on aesthetics and emotions -- not on what I can hear.

Lots of amps use autoformers. It's just another kind of transformer. 

I completely agree with Stan. The entire point of the autoformers in a Mac amp are to allow the gain devices to behave in as linear a manner as possible by relieving them of the responsibility of actually taking control of the speakers. That's fine and dandy if you like speakers that make it a point to present the most benign load possible to the amp. But if you like speakers that actually get reactive and expect the amp to actually take control, as most speakers do, then a Mac isn't the amp for you. Because the autoformers isolate the output stage from the rough and tumble world of speakers, the amp is limited in it's ability to drive more current into an impedance dip or less into a spike, as the speaker designer expects an amp to do, and that drives the speakers into nonlinear response. 

I believe Ralph Karsten (Atmasphere) has weighed in on this topic many times in the past.  I recall that Ralph has suggested the use of Zeros, an outboard autoformer, in certain instances, e.g., driving extremely low impedance electrostats.  

As to the points above about tube amps and their use of output trannies, ... the answer there can depend.  For example, my amp is an ARC Ref 150 SE.  It is a tube amp that uses output trannies.  However, ARC also uses some negative feedback to lower the output impedance and extend the bandwidth.  For example, the output impedance off the 8 ohm tap is about 1 ohm or less; about half that off the 4 ohm tap.  

What this means in practical terms is that my amp can perform "somewhat" like a low impedance solid state amp when driving speakers with varying impedance and phase angle curves, …. within reason.

I only use my amp as example.  For those interested in tube amps, check Ralph's white paper that explains the Voltage and Power Paradigms.  For most tubes amps, it is not an all or nothing proposition.  It's a spectrum issue.

BIF   

Now there are even CAR stereo amps that can run .5 ohms all day at negligible distortion.

The problem with not using transformers, even with solid state amps is that 'negligible distortion'.
It is the mark of a good engineer to know what is negligible and what is not.
The slight amount of distortion made by most solid state amps is not negligible. The reason is that the distortion is composed almost entirely of higher ordered harmonics, and the human ear is tuned to these harmonics in several ways, a sort of convergence.
First, there is Fletcher Munson- the loudness curve. If you take a look at it, you will see that the ear is most sensitive at birdsong frequencies- up to 7KHz. This is why alarms are higher frequency. There are a lot of instrument fundamentals that are a lot lower- in particular, instruments that are near 1KHz will have a 7th that high- but here's the tickler: the 7th is also one of the harmonics that all solid state amps have in common (which we've known since the 1930s imparts a metallic quality to the sound), and the ear is insanely sensitive to this (moreso than good quality test equipment), because it also uses that and other higher orders to sense sound pressure. This is why solid state sounds bright and harsh, its why tubes are still being made and why we argue about tubes and solid state endlessly on the internet.

So this is a problem, but actually an easy solution is to simply present a higher impedance load to the output section of the solid state amp. Right away it will make less of these higher orders and so will sound smoother and more detailed. That's what the autoformer is for!
One other point- its not to anyone's advantage to make **any** amplifier work hard! You can know right away that if you do so, it will have higher distortion. In this regard, if the most realistic audio reproduction is your goal, your amplifier investment dollar will always be better served by a speaker that is higher impedance- 8 ohms or more. There is little point to 4 ohms unless sound pressure is your goal rather than sound quality.

I'm by no means an engineer, but very much appreciate the technical descriptions of why some amplifiers are designed with autoformers.

One comment about McIntosh owning the patent.  The patent on that invention expired long ago.  I think the more viable reason more amplifier manufacturers don't use output transformers for solid state amps is the cost and how much weight it adds to the unit.

I spent about a year visiting all sorts of shops to shop for a new pair of speakers.  The pair I finally selected (Focal Sopra No2's) match up with the MC452 "quad balanced" amplifier from McIntosh.  I've heard those speakers driven by amps which were called "fast" or "more detailed" (higher damping factor?), but the Mac (to me) just sounded more "musical" than the others.  Could it be the autoformer?  Maybe.  But I wouldn't sweat it if it was not!

There is a reason why they retain value, and I really don't believe that it is the blue meters. They sound good, and from my experience, the amps with autoformers have more authority and "gravitas" I guess I'd say.

The only negative with Mac autoformers is in doubling the amplifier cost and weight.

I have been looking at integrated amps and when researching the Mac I noticed the only ones without auotformers are the lowest rated at 100w. I wonder why that would be the case are they not needed in the low watt amps? I assume they could use them just as easy in a 100w integrated as a 200w integrated. I belive they use the autoformer in all the new power amps even the lowest 150w mc152. I don't own one or know  that much about it just curious why only the low watt amps don't have them ? Could it be they are meant to be used in smaller rooms with easier to drive speakers? 

" The only negative with Mac autoformers is in doubling the amplifier cost and weight"

So true!  I had to get help from my neighbor to get the carton from my car into the house, get the beast unboxed, unbolted from the plywood base, and lifted up onto my wall unit!

"I have been looking at integrated amps and when researching the Mac I noticed the only ones without auotformers are the lowest rated at 100w. I wonder why that would be the case are they not needed in the low watt amps? I assume they could use them just as easy in a 100w integrated as a 200w integrated.

My guess is that this is strictly a marketing issue, by not including autoformers in low power amp they are offering entry level Mac products  for those who do not need big power, big weight and big price tag but still like to own a McIntosh.

After owning a newer solid state amp from McIntosh with autoformers, I have come to believe it is their attempt to have the amp take on some of the characteristics of a tube amp. This myself was confirmed that the bass produced was loose and did not have the impact/slam of a Direct Coupled amp. Further I felt the midrange was more on par with a tube amp in that it was full and fleshed out.

That is the first time I’ve heard a claim that the autoformer was a hindrance to better performance;

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.

stanwal
For us non Mac enthusiasts the autoformer has always been proof positive that Mac had no idea how to design a transistor amp, perhaps they are coming to their senses at last.

+1

nsgarch

I agree with Stan. I just wrote this a few minutes ago:
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1262654269&read&3&zzlNolitan&& Report this

+1

Cheers George

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!!!

Thanks George.

Honestly, I think the big thing is taste. 

From the perspective of creating an ideal voltage source, the autotransformer is garbage, but if that tickles your ears, and it is your money, then that's what you should get. 

That simple. 

Best,

E