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Autotransformers - why does McIntosh use them?

The one major item people miss is the autoformer enables an amplifier to have a large power output using lower voltage rails that use the output devices as current amplifiers well within their safe operating areas thus giving less distortion and higher reliability. The ability to give the devices an ideal match no matter what load is presented allows the designer to concentrate on lower distortion and higher reliability using lower voltage high current output transistors.
 
Well, there's a good point!
It's consistent with Mac's early vacuum tube philosophy, too, as I know that some if not all of the vintage Mac vacuum tube amps tended to run the tubes quite conservatively.
 
The small added cost of quality autoformers would not deter manufacturers of the best ss amps such as Boulder, Gryphon, DarTZeel, Mark Levinson, Lamm, Pass, and many others in their class, if it was felt they provided a sonic advantage; but they don't. Let's see if we can find out why . . . . . . . . .
 
nsgarch said:
The small added cost of quality autoformers would not deter manufacturers of the best ss amps such as Boulder, Gryphon, DarTZeel, Mark Levinson, Lamm, Pass, and many others in their class, if it was felt they provided a sonic advantage; but they don't. Let's see if we can find out why . . . . . . . . .
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I suspect that the focus on certain aspects of the design criteria are different between each of those companies and I'd bet that sound and build quality are at the top of each of there lists as 1A and 1B on their list of importance. It's the other items in that criteria that will have more an effect on the path they take to reach their high quality sound. I don't think that you'll find any of those companies having more or less focus on sonic purity than any other. And that "small added cost" would probably be sitting at position number 1 or 2 in highest cost component on the BoM. Might be a smallish percentage of retail costs, but in terms of the parts used in the amp, it would be one of the single most expensive parts.
 
:the question I was asking was about autotransformers affecting the sound negatively.
thanks,

It's not the autoformers that affect the sound, It's the Power Guard circuit:thumbsdn:
 
dnewma04 said:
And that "small added cost" would probably be sitting at position number 1 or 2 in highest cost component on the BoM. Might be a smallish percentage of retail costs, but in terms of the parts used in the amp, it would be one of the single most expensive parts.
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As parts go it isn't expensive; it's just a single winding (usually air core) transformer, once again see Paul Speltz's website. My point was that even if it was an expensive part, those other manufacturers wouldn't hesitate using it if it meant better performance. I think Mac has them chiefly to make their equipment more user friendly (i.e. harder to damage by those without any audio smarts at all). I'm not sure how or how much the inductance of the autoformer affects sonics, but has to to some degree. The device doesn't seem to reduce damping factor to any great degree though, which is the main problem with tube amp iron core output transformers.
 
Next to possibly the power transformer, what part of the amplifier would cost more than the autoformers? Perhaps, it has negative effects on sonics but maybe the advantages of the autoformers having a more consistent operating point overcomes any detriment the inductance causes? Different strokes for different folks, I suppose.
 
A power transformer is a whole different animal. It generally has an expensive (and heavy!) laminated core, at least two windings, and miles more wire.
 
nsgarch said:
A power transformer is a whole different animal. It generally has an expensive (and heavy!) laminated core, at least two windings, and miles more wire.
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Are you intentionally being evasive? Autoformers aren't cheap to mfg and would be one of the most expensive components of any amp they are used in.
 
I for one am rather bored with this topic. Detriment to the sound, why, why not... having had no less than a dozen of high end ss amps that didn't have autoformers not to mention a half dozen tube amps and having listened to just about every respected brand out there over the years whether at the dealer or one of my friend's houses, I think I would have heard something if the difference was even there. I don't think I am deaf just yet, nor do I think are all the people who have praised the McIntosh autoformer amps in various publications over the years and the numerous awards they won.
 
I for one am rather bored with this topic. Detriment to the sound, why, why not...
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Well, I am not bored with this topic. It's interesting to me that I still haven't heard a explaination of whether autoformers add or subtract from the sound and why others state that autoformers are not necessary in modern amplifier designs. I am not bashing McIntosh. I own McIntosh equipment. I am interested in why other people feel this way about autoformers. Just a friendly exchange in ideas. No reason to get worked up about this topic.
Jim
 
How can you know with any certainty whether an autofromer negatively impacts the sound. The MAc amps are sepciofically designed with the autoformer as part of the circuit topology. Other high end amps like Levinson, Krell, Ayre, etc are specifically designed without autoformers as part of the circuit. Can you test a Mac amp with and without the autoformer? No. So how do you know if the autoformer negatively impacts the sound as the original post asked? You can't. What you can do is audition Mac and non-Mac amps and decide which one you like best and live with the decision. Clearly there are a lot of very good, very well made amps (and other components) both Mac and non that are available. We're starting to get into the realm of how many angels fit on the head of a pin.
 
jjay said:
It's interesting to me that I still haven't heard a explaination of whether autoformers add or subtract from the sound and why others state that autoformers are not necessary in modern amplifier designs.
Jim
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Jim, I believe your original question and continued interest is somewhat intuitive. You seem to be assuming that there might be an adverse affect just because of what you read on other forums. Unless you and others can be more specific, this notion is without merit. To my knowledge there is no imperical evidence that autoformer design necessarily improves or detracts from sound compared to other designs under optimum conditions. However, we do know that that autoformers provide a successful technical solution to some engineering problems outside of optimum conditions that other designs do not solve. I believe the previous explanation by Serge adequately addresses how autoformers improve overall operation and thus contribute to the avoidance of inferior sound characteristics.
 
Jim, I believe your original question and continued interest is somewhat intuitive. You seem to be assuming that there might be an adverse affect just because of what you read on other forums. Unless you and others can be more specific, this notion is without merit.
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William, You are correct. I wish I could be more specific but I do not have the expertise or knowledge about autoformers or other amplifier designs. That is what is so great about the forum. Many members with tons of experience I can get advice from. As I stated before, I was just curious about autotransformers. I was not commenting positively or negatively about McIntosh amplifiers. I own one and love it.
Jim
 
I do not have the knowledge to understand what autoformers do and how they impact sound quality, All the Mac amps that I have owned in the past 30years came with the autoformers and they do sound just fine but so do some other top brands that do not have them.
One thing is certain, these things double the weight and the cost, perhaps this is one reason why some manufacturers do not see enough benefits to justify implementing autoformers in their designs.

Vahe
 
I can imagine a lil break room in the high falootn' amp makers office...The engineers want to use autoformers but the power people dont want to as it would be a tilt of the hat to McIntosh for sticking with what works..

Mr Levinson, I recommend we use Autof'rs...
nah...we dont wanna be bunched up with McIntosh..

To the original poster: There is no answer to the question...its all opinions. Do you really think that McIntosh would be what it is today if they used a designed that compromised sound quality? no...so its all a matter of opinion, conjecture, and bias.
 
just to add my .02c - I've owned a few solid-state amps in my time (even though I'm a tube guy at heart) and none of them have come close to the sonics of my ancient 250. I recently bought it on a whim, admittedly just for the looks of the beast and was quite surprised how good it sounds.

I do believe the autoformer plays a large part in this - allowing the output transistors to work into an optimal (static) load. This will also protect the output devices from the outside world a bit more (ie - varying imedance loads, etc) Obviously most other designers found another route, using massive heatsinks and overbuilt power supplies to allow the output stage to deliver the current into just about any load (anyone remember the arc-welding article using M-L gear?) McIntosh went a different engineering way and the results speak for themselves.

Of course the skeptical side of me says McIntosh added the autoformer so they wouldn't have to fire a bunch of their tube transformer winders ;)
 
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