Someone is selling a MAC MA6500 Integrated claiming its superiority over the Ma6600 due to the fact that "it does not have the degrading autoformer design found in the MA6600". That is the first time I've heard a claim that the autoformer was a hindrance to better performance; I thought quite the opposite. What do you MAC Maves think?
bifwynne I am confused. I get using autoformers on high output impedance tube amps. The autoformes will make the amp think it is driving a higher impedance speaker load and thereby improve the damping factor, make the load easier for the tube amp to drive and may smooth out the FR of the speaker.
But why would one use an autoformer on a high quality, stable, hog wattage SS amp. These beasts were (should be designed) to handle demanding speaker loads. I surmise that most speakers on the market today were voiced to be driven by a high current capable voltage paradigm SS amps.
It’s simple! It’s two things, a gimmick, or a band-aid for gutless amps that can’t drive those loads.
It’s not a patented idea, all you you have to do is to look at how many other "well known" well designed solid state hiend amp maker use output transformers? A BIG ZERO, if they did it was as a gimmick or an aid for that amp to drive speakers they normally couldn’t.
Why do good OTL’s tubes not use them on speakers they’re comfortable with?? BECAUSE THEY SOUND BETTER WITHOUT THEM (Ralph), so long as the speaker load is ok for them. The moment the load get’s too difficult for them with other speakers then they’re better using an autoformer, I would change the amp instead.
I am confused. I get using autoformers on high output impedance tube amps. The autoformes will make the amp think it is driving a higher impedance speaker load and thereby improve the damping factor, make the load easier for the tube amp to drive and may smooth out the FR of the speaker.
But why would one use an autoformer on a high quality, stable, hog wattage SS amp. These beasts were (should be designed) to handle demanding speaker loads. I surmise that most speakers on the market today were voiced to be driven by a high current capable voltage paradigm SS amps.
Maybe autoformers make sense on super low impedance electrostats,but I'd be careful on the front end in matching up any amp to a super low impedance electrostat. Make it easy in yourself and just short the amp's output terminals and call it a day. :)
In my case, my McIntosh MC452 pairs really well with my Focal Sopra No2 speakers, I can listen to them for many hours without fatigue. I enjoy this combination very much, very much the only thing I really care about.
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.
This statement is false. The reason is that in a Mac, the autoformer is included in the feedback loop (this fact is also ignored by @unsound). Further, any kind of output transformer does not provide 'isolation' as suggested above, instead it **transforms** impedance. So in this way, a variation of speaker impedance is transformed to a variation in load impedance to the output transistors (but at a different impedance as defined by the transformer or autoformer) and they respond in kind. Ringing and oscillation is a red herring - ringing is handled by the feedback, and if anything, the amp is less likely to oscillate when a transformer is employed!
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?
This is a bit of a digression on this thread. If others are interested in this topic, I recommend a new thread:
Actually tubes can handle speakers with variable speaker loads and do just fine- the Sound Labs ESLs are good example. Like all ESLs, their impedance varies by about 10:1 over their entire range, and tubes can usually manage them better than solid state. With regards to output impedance, a high output impedance does not imply universal frequency response colorations. It does mean that you will have to be more careful about the match between amp and speaker, but IME this is an issue regardless of the amp and speaker anyway :)
The elephant in the room is the fact that the ear converts distortion into tonality- and in this regard the ear has tipping points where the tonality of distortion is favored over actual frequency response. IOW, it can be more important to get rid of the colorations caused by distortion than it is to have perfectly flat frequency response; if you look at speaker response curves, the latter does not exist anyway! The ear is far more sensitive to higher ordered harmonics than it is lower orders, by several orders of magnitude. This is why solid state amps can have the coloration of 'bright' and 'harsh' despite having very low overall THD. By not running feedback, it is possible to reduce these higher ordered harmonics if the circuit employs good design principles (in other words, has good open loop linearity). This is far easier to do with tubes than transistors! There are good solid state designs with zero feedback, but they are rare.
An alternative to zero feedback is to use an autoformer that allows the output transistors to drive a higher impedance. In this way higher ordered harmonics are suppressed as all amplifiers make less distortion into higher impedances. The downside is that overall, the amp makes less power on account of that higher impedance. But in the world of high end, lower distortion is far more important then overall power.
So here is the question: a speaker with huge variation in impedance curve will receive considerably more power where the impedance deeps way below its average curve
I am going all out to prove my ignorance and ask a question
on autoformers.
I suppose we all agree that one advantage of autoformers is
to deliver the same amount of power regardless of variations in a given speaker
impedance curve.
So here is the question: a speaker with huge variation in
impedance curve will receive considerably more power where the impedance deeps
way below its average curve, and if that speaker in fact receives more power at
certain frequencies then those frequencies will be greatly highlighted, so
there goes your flat response!
It seems you are consistently more interested in the technical data on hifi equipment that I'll bet determines what system or systems you own and like.
Do you ever throw care to the wind and just trust your ears?
I alwasy do both Pops. As do all designer of good amps, without bench testing, laws of electronics, tech data, if you bought such an amp off some who doesn't do these you'd have a pile of junk.
The crossover is at 2KHz and the sensitivity would have been matched at that point to the mid range. Note the impedance is quite high at 2KHz and drops rapidly above 2KHz - perhaps the crossover design may not be ideal as the revalator tweeter resonance is much lower (500Hz).
….Because despite the never ending reports over the last 50 years of the amps not using autoformers overheating, destroying speakers and causing fires, consumers keep buying them in such vast quantities as to provide a huge and continuing to grow sample size for such inspection?
What is failed to be mentioned is that with most loudspeakers as impedance decreases / sensitivity decreases and as impedance increases / sensitivity increases. So if the speakers presents an impedance that swings between the impedances of the taps there will be potential for corruption to the ouput linerity.
@georgelowfi - sorry, couldn't resist the jab since you ended your last post with one to roxy54.
It seems you are consistently more interested in the technical data on hifi equipment that I'll bet determines what system or systems you own and like.
Do you ever throw care to the wind and just trust your ears?
If I did that, the test would be compromised by the fact that the amp used in the test was not designed to be used with autoformers. I really wish that you could have been in my listening room about 9 years ago. I was using at that time a Mac MC 300 and occasionally a Mac MC 2105 which I still own and use periodically. Anyway, I got the audiophile itch, and the darling at the time was the Pass Labs X250.5. I sold my MC300 and bought a perfect one on Audiogon from a member who, coincidentally sold it to buy Mac 501 monos, and later admitted to me that he was so much happier with them than he had ever been with the Pass. Anyway, that amp was so pretty, and I was expecting this new generation wonder to show the Mac a clean set of heels as the Brits say. I was in for a surprise. I used it with 4 different sets of speakers, and with ALL of them, it sounded thin and transistory. My best audio buddy agreed; and believe me, I wanted to like this amp after having just sold my Mac to get it. I tried extended warm ups, different cables etc. It was, as you said, put up for sale "quick as a flash". I use an 8 watt 300b, a 40 watt class A integrated and a Mac 2105. I'm not really what you'd call a Mac fanboy; more of a mature listener who knows what he likes when he hears it, regardless of the technology that was used to achieve that sound. My point to you is less about defending McIntosh and their circuit topology, and more about judging gear, any gear, on the merits of its performance, and not how "correct " it is the estimation of electrical engineers. I've been through quite a few amps, more than some and surely less than others, but if the Macs weren't better than most of what I've owned, I wouldn't still be using one.
Roxy? What I'm saying is simple, if an autoformer sounds better with a ss amp into a speaker that amp wasn't a good match for that speaker to start with. I noticed your avatar and it looks to be one of those amps that would benefit from an autotransformer into speakers it normally shouldn't be mated with. So your happy if it does.
You can prove this to your self, there are a number of Zero for sale used some as low as $250 for the pair, put them on a known "good" Solid State amp that can drive most speakers, and you will put them back up for sale quick as a flash.
Sure George, whatever you say. This is getting more ridiculous by the minute. It's a shame that listeners all over the world don't listen to you and unsound (good name) and realize that they're wasting their money on this outdated garbage.
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.
"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?
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.
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.
Thanks Erik, Taste is what it’s all about. Saying that autoformers are a fix for a flawed amplifier design as Stanwal said is in my view just ignorant. It is just another way of going about things, and for some of us, myself included, it produces a very good result.
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.
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.
"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."
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.
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.
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.
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.
"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.
"
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. 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?
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.
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!
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 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.
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.
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.
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.
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
You must have a verified phone number and physical address in order to post in the Audiogon Forums. Please return to Audiogon.com and complete this step. If you have any questions please contact Support.
