Dissing the McIntosh Autoformers?

Has anyone read this?

http://groups.google.com/group/rec....eb249fe11b8/7cba237375d677c6#7cba237375d677c6

Seems there's a school of though out that the Autoformer idea is like a 5th and 6th wheel on a car. Add expenses without any gain. What's surprised me is that no one's argued FOR the Autoformers.
I've always thought there were many advantages to the Autoformers, and have always wondered why other companies don't use them. But my electrical/engineering knowleage is not quite up there to put my neck out and argue with them. Thought it might be of interest to people though.

Interesting link. The two main characters are Brent and Trevor. It seems to me that while Brent is looking for solid, intelligent reasons, pro and con, about output transformers, all Trevor is doing is bashing McIntosh and not backing up any of his claims.

Back in the 1970's I got fed up with this kind of crap from my "friends" that were also into audio. Perhaps I should say "some of my friends," because others were more intelligent and mautre about it - they enjoyed what they had and maybe discussed what they liked about it, and I did the same with my McIntosh gear. Neither of us would bash the other's choices or equipment. You'll notice that Trevor, the main opponent of output transformers in the Google discussion, gets pretty heated and insulting in his dismissal of McIntosh's reasoning about autoformers. Trevor even attacks Brent personally at one point: "You don't read very well, do you?" (addressed to Brent). This does nothing to make any point about autoformers, and is rude and insulting.

Trevor makes assertions, such as: "A constant load is neither necessary, nor desirable for SS amplifiers." But he never backs them up. I mean, why is a constant load not necessary or desirable in a SS amp? He never tells us why, just expects us to take his statement on faith. Some of his statements are so obviously false that it greatly diminishes his credibility. For example, in response to a question by Brent, about why McIntosh is the only company offering output autoformers on SS amps, Trevor asserts:
"Because:

* It is VERY expensive.
* It damages the performance of any properly designed SS amp.
* It increases the mass of the amplifier significantly, for no performance
benefit.
* It INCREASES output impedance figures.
* It buggers up the frequency response.
* It increases distortion.
* McIntosh are desperate to differentiate their product from all the other,
quite reasonable, products in the market place. It is their Unique Selling
Proposition."

Note that Trevor does not back up or support any of these erroneous conclusions. Why are they so? But, you doubtlessly noticed that they are not even remotely true to begin with, so he can't support them. Except for that autoformers are, indeed, very expensive. If he would drop the last part of his assertion about autoformers increasing mass of the unit, he would be right on that one too. They are heavy. But the rest of his claims - pure hogwash. Do McIntosh autoformer amps have distortion problems? NO! The MC 2105 I bought in 1971 was producing its rated output at less than a fifth of its rated distorion when it was seven years old, had been "marked as territory" by two @#$%#%!! male siamese cats (hmmm, what's that smell?), and later dripped on by water from the apartment above me until it shorted something out and blew its fuse. And the current MC1201 tests out to have only the residual distortion from the distortion analyzer's oscillator. Both have output transformers. Mc amps have "buggered up" frequency response? No. Check the specs and see for your self.

My point? Look for a reasoned argument ("argument" does not mean "fight") and mature conduct. Trevor demonstrates neither in his posts to Google. Most audiophiles appreciate a good, well-informed discussion, backed up by verifiable fact, and conducted in a mature and respectful manner. Most also have learned to ignore the type of angry, hostile, and unsupported rant put forth by Trevor.

To reply to your original post: The sum and substence of the thread at Google is that Brent has asked about autoformers, no one has put forth any fact-based answers, pro or con, yet.

I do have a McIntosh white paper, by Sidney Corderman, about transformers and solid-state amplifiers. While I am very busy with other things now, I will try to get to read it over and post some of the reasons for McIntosh's use of autoformers. Post will be here, not Google, as the discussions are more mature and intelligent here.

Here's some stuff posted by Ron_C on audiogon about autoformers.10-28-04: ron-c-mcintosh@msn.com
Sean,
. With todays modern high speed output transistors this bandwidth is obtainable where the devices were the limiting factor until the early 90s. The McIntosh output autoformer uses a grain oriented steel core with a very large winding made up of groups of wire. The actual gage is high and these are terminated at about 12 gage total for each tap. Unlike a tube amp where the transformer is converting an impedance ratio of 125 to 1 in a McIntosh unity coupled tube amp, or 250 to 1 in other tube amps, the solid state autoformer is 4 to 1 or less depending on the tap.
If an amp is to be reliable and stable something will have to be placed across the output section, either a cap or choke coil or speaker wires with little boxes of Zobel networks in them. The autoformer is less intrusive and has the advantage of impedance matching. The drawback is cost and weight while the advantage is cool operation, long life, and output impedance flexibility.
In the case of the Quad Balanced amps like the MC352 the two amp sections per channel are balanced in the autoformer and not to chassis ground. If a direct coupled amp is 'balanced' it is actually bridged to chassis ground and will have a max signal to noise ratio of -112 db. In the case of the quad balanced amps the autoformer allows the ground point to float and -124 dB SN is achieved.
The McIntosh autoformer will introduce 0 degrees of phase shift at 20 Hz and less than 3 degrees at 20 KHz. The average volume control on a pre amp will introduce about 15 degrees of phase shift.
McIntosh has never made a big deal out of dampening factor. The old amps from the 50s typically had dampening factors of 10 or 20 while the new ones are rated at higher, 40 in the case of the MC352. The main concern with deep bass performance is usually power and lack of phase shift.
I have an old MI200 tube amp running a double 12 inch sub, This is a mono, 200 watt amp using transmitter 8005 triodes at 1000 volts. This amp has a dampening factor of 10 yet very few transistor amps will deliver the clean effortless bass of this amp. A low dampening factor does

More on the subject from a Ron-C post: The two amps in each channel are floated above chassis ground. The autoformer is a transformer with a coil of wire that ends in a ground point. The two amps feeding the autoformer produce one half of the sine wave each and are combined in the autoformer. The amps crossover point will float to maintain balance and if one of the amps is shorted out the other amp will complete the sine wave at its 225 watts. This design is called Quad balanced by McIntosh and will result in a signal to noise ratio of over 124 dB. This design of course uses common mode rejection.
Like a direct coupled amp the MC352 will double power if say a 2 ohm load is put on the four ohm tap. Heat and current draw will also go up. Unlike a direct coupled amp the MC352 will not halve power as the impedance is increased. With the MC you get all the power you pay for regardless of the speaker used.
The output autoformer allows the amp section to be designed for maximum linearity and efficiency which may result in say an impedance of 2.37 ohms. Since there are not a lot of 2.37 ohm speakers the autoformer is then taped to yield the 2,4, and 8 ohm point. This results in an increase in power over compromised direct coupled designs.
The autoformer has a greater bandwidth and power capability than the amp section which drives it. The MC will put out rated power to 100 KHz and swing high output current. The autoformer is an audio 'transmission' to match the amp to a variety of loads. In no way is a properly designed and built autoformer a 'buffer'.
ron-C

Could not have said it better myself! The autoformer McIntosh amps allow you to get 'All The Power You Paid For'. All direct coupled amps (except the MC207 which has the same power into 4 or 8 ohms) must be designed to deliver full power into a specified impedance. If the speakers you use are not that same impedance as the amp designer had in mind you will not get the output the amp is advertised to have or the safe operating characteristics of the amp will be exceeded.

The autoformer in our latest designs allows lower distortion, higher signal to noise, and massive power output. The new MC2kW mono amp is 2000 watts at less than .005% distortion and -127 Db signal to noise ratio. It will do this at 10 Hz or 50 KHz through the autoformer by the way.

As far as hacking on the old MC2105 that first series of McIntosh SS amps are still going strong today where most of the competing designs are at the dump. We used the best output devices available then as we do now and these amps are still serviceable after 40 years.

Ron-C

Great discussion! Can't really understand why anybody in their right mind would bash McIntosh? First of all anyone who has used a Mac amp with some sincerity would attest how distinctly listenable their solid state amps are compared to anything else that was available in the 70s or 80s, and to a great extent even today. Tansformer coupled output provides a motion to the signal that capacitors can't do, and besides impedance matching is of utmost importance too. Way back, when Mac gear was out of my reach, I used to experiment with UTC transformers at the outputs of run of the mill SS amps to make them more palatable; a 4 ohm load will sound better if it can be made to appear as an 8 ohm load to the amp, etc., of course the tradeoff will be output power. I don't know of a good way to do this without an autoformer.

ron-c said:

If the speakers you use are not that same impedance as the amp designer had in mind you will not get the output the amp is advertised to have or the safe operating characteristics of the amp will be exceeded.

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Does this mean that Mc amps with autoformers will perform better than DC-coupled amps with speakers that have "difficult" impedance loads such as electrostatics?

On the 2 ohm tap Mc amps will drive a 1 ohm load all day long. Autoformer coupled amps do change there output as the load varies. The autoformer is a continuous wire back to the transistors in the output stage.

Ron-C

Ron ... I still don't fully understand. True, some ESLs go down real low in term of impedance, but the bigger issue by my understanding is the "wild" impedance swings. From as high 100 ohms down to 2 ohms over the frequency range. Do autoformers provide an advantage in this situation too?

Any of the taps, 2, 4, or 8 ohms on the autoformer will work below one half the taped value. So 1 ohm loads will work on the 2 ohm tap. A one ohm load on direct coupled amps set up for four ohms will cause problems such as current limiting, shut down, thermal overheating, fuses blowing, etc.

As far as a rising impedance the autoformer coupled design will lower power as the impedance rises, just like other amps. That is the way transistors work. There is no reason for the impedance of any modern speaker to swing above 10 ohms that I know of and these peaks are at the crossover points.
A speaker designer measures the response of their design as they sweep the speaker connected to an amp. This is all part of the design how the amp will react to the impedance swings.

Ron-C

I almost joined just to tell Trevor that he is retarded.

Here's a '59 Edsel, courtesy of edsel.com. I see a hint of a '58 Chevy on the rear quarter and the vertical grill, while unique, is similar in concept to the split grills on '59 and later Pontiacs. Of course, the Edsel grille is a lot more dramatic.

Murray

Well, I did and did a long rant. I had hoped this type of anti-Mc garbaged was going away. Not 1 of then even hinted at owning and using a Mc and simply not liking the sound. At least that would earn some respect. Sonic preference is personal to the person.

ron-c said:

There is no reason for the impedance of any modern speaker to swing above 10 ohms that I know of and these peaks are at the crossover points.

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That's interesting Ron because when I've often looked at the test specs by JA in Stereophile of speakers, I recall seeomg a lot of variation with peaks well above 10 Ohms. Maybe I should look more closely.

For example, my Klipsch Forte's which were tested way back when by Julian Hirsch in Stereo Review have an impedance peak around 60 Ohms (!) and a low of around 3.7 Ohms. Thank God they are super-effecient (99db/w/m) but I can imagine this is surely a "difficult" load for any amp. I've read that the Quad ESL 63/988 has a huge impedance swing.

So, I'm not going there....

responding to folks who talk with little reference to their comments do not interest me. I, for myself, know how the Mac stuff is designed and the fact that they've been doing it for over 50 years speaks louder than anyone online with their CAPS LOCK key stuck in the on position.

'Nuff said.

Cheers,

David

dshoaf said:

responding to folks who talk with little reference to their comments do not interest me.

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Somebody should take up Brad on his esteem for Crown gear. God, the DC-300A I once listed to was absolutely aweful. Fine for a PA system, but not the home.

Golly. Edsels, dog turds and now Waffen SS. Edsels with 5 and then 6 wheels.

Here's a '58 Bonneville (thanks to kingoftheroad.net.) One look at this and you can see why no one bought Edsels. I'll try and find a '58 Impala.

Murray

So, here's a '58 Impala with appreciation to classicroad.com. It's easy to see the family resemblance to the Pontiac. When I was a kid, I thought these and the Pontiacs were the best looking cars. Don't care for the "continental kit" and actually these were pretty rare.

Oh. Some of you may be wondering what the heck this has to do with McIntosh autoformers. Nothing.

Murray

Murray, your point is made beautifully and with elegance.