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?
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.
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.
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.
"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?
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.
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.
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.
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.
@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?
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.
….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?
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).
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.
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!
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 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.
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 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. :)
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.
Thank you Ralph for keeping it honest and cutting through the misinformation. Certain individuals keep polluting the threads with personal opinions based on complete ignorance. I now simply scroll over their posts.
Well, my last post was removed because I mentioned another audio website. I was saying that there is a recent review of the new McIntosh 611 monoblocks if anyone cares to read it and see how "poorly designed" the reviewer found them to be.
You shouldn't question what they do, they have their job moderating and are good at it. Like I said I doubt very much the post was deleted because of a reference to another audio website, it was probably whatever else was said, in the way it was said.
With easily driven speakers ( impedance ), I much prefer the Mac amps without the autoformers. Same with OTL tube amps. But, let us be real. Many fine speakers are not easy to drive, and autoformers are there to keep the amplifier safe and sound ( pun intended ) and better match the speaker. Enjoy ! MrD.
But, let us be real. Many fine speakers are not easy to drive, and autoformers are there to keep the amplifier safe and sound ( pun intended ) and better match the speaker. Enjoy ! MrD.
These speakers then should have different amps that can handle their loads.
I clicked on a link within the post that attempts to tout the benefits of an Autoformer; essentially better matching to speakers with different impedance values. Ie 4 ohm taps to 4 ohm speakers, etc. All well and good for “nominal impedance”.
But what about speakers with impedance swings all over the place, from 3 ohms to off the charts well at well over 20 ohms like 802D3s (nominally 8ohms). It’s swings like this that tax the best tube amps with their transformer outputs. How, exactly, do these impedance swings effect autoformers???
Are the electrical properties of autoformers similar enough to those of tube output transformers to cause similar issues when driving speakers with crazy impedance and phase curves?
But what about speakers with impedance swings all over the place, from 3
ohms to off the charts well at well over 20 ohms like 802D3s (nominally
8ohms). It’s swings like this that tax the best tube amps with their
transformer outputs. How, exactly, do these impedance swings effect
autoformers???
Are the electrical properties of autoformers
similar enough to those of tube output transformers to cause similar
issues when driving speakers with crazy impedance and phase curves?
Ralph, could you clarify a point regarding impedance matching between tube amps and speakers with roller coaster impedance and phase angles numbers.
I think you mentioned that the function of an output transformer is to step down the high voltage from the output tubes to the amps output taps. In addition, the output tranny will step up a speaker's impedance presented to the output power tubes at the primary windings of the tranny.
Maybe a simple example will help further clarify my understanding. My amp is an ARC Ref 150SE which uses KT-150 tubes in push-pull fashion. I recall that the output impedance of KT-150s is 3000 ohms. In a theoretically perfect world, if I had a speaker with a perfectly flat 4 ohm impedance function, plugging the speakers into the amps' 4 ohm taps would result in a stepped up impedance of 3000 ohms presented off the primary windings of the output tranny. That would be a perfect match with the power tube's output impedance.
We all know that in the real world, most speakers have roller coater impedance functions. As a result, the impedance off the primary windings of the output transformer will vary from the optimal 3000 ohm target. ARC says, just use the taps that sound the best.
So here is my question. What is happening electrically if there is an impedance mismatch? Is the amp producing distortion if there is an impedance deviation from 3000 ohms? If so, does having larger wattage and power supply capabilities ameliorate distortion effects?
How about negative feedback? In my case, I understand that the Ref 150 uses 14db of negative feedback and as a result, performs like a voltage source amp. Does that feature help to reduce distortion effects?
I have not touched on phase angle or sonic coloration issues caused by impedance mismatches between the amp's output taps (nominally, the 4, 8 or 16 ohm taps) and the speaker's actual impedance at a particular frequency.
As to sonic coloration, I recall that the output impedance of the ARC Ref 150 off the 8 ohm taps is around 1 ohm or less. This results in some sonic coloration, ... but not a lot. In a Stereophile review of the ARC Ref 150, John Atkinson measured the Ref 150's voltage output variation off the 8 ohm taps to be (+) or (-) .8 db when presented with a synthetic speaker load.
Btw, are similar issues presented with OTL tube amps?
In my case I have a McIntosh MC452 (solid state amp with autoformers) driving a pair of Focal Sopra No2 speakers. Focal lists the "nominal" impedance at 8 ohms, but the "minimum" impedance at 3.1 ohms, so my dealer recommended that I connect them to the 4 ohm taps on the amplifier.
I have to admit that I was quite pleasantly surprised to see the amp double down from it's 8 Ohm tap down to 4 Ohms, but from there down to 2 Ohms, it was even worse than I expected.
was quite pleasantly surprised to see the amp double down from it’s 8 Ohm tap down to 4 Ohms
If you don’t change the tap, it doesn’t double at all when the load impedance halves from 8 to 4ohms And you can’t change the trany tap from 8 to 4 half way through a musical note, when it decides to dip from 8ohm to 4ohms then back up again. Autoformers good interim fix for amp/speakers if the amp can’t drive the speaker without it, till you get the right amp
So here is my question. What is happening electrically if there is an
impedance mismatch? Is the amp producing distortion if there is an
impedance deviation from 3000 ohms? If so, does having larger wattage
and power supply capabilities ameliorate distortion effects?
How
about negative feedback? In my case, I understand that the Ref 150
uses 14db of negative feedback and as a result, performs like a voltage
source amp. Does that feature help to reduce distortion effects?
I
have not touched on phase angle or sonic coloration issues caused by
impedance mismatches between the amp's output taps (nominally, the 4, 8
or 16 ohm taps) and the speaker's actual impedance at a particular
frequency.
As to sonic coloration, I recall that the output
impedance of the ARC Ref 150 off the 8 ohm taps is around 1 ohm or
less. This results in some sonic coloration, ... but not a lot. In a
Stereophile review of the ARC Ref 150, John Atkinson measured the Ref
150's voltage output variation off the 8 ohm taps to be (+) or (-) .8 db
when presented with a synthetic speaker load.
Btw, are similar issues presented with OTL tube amps?
@bifwynne
All amps always make distortion. If the amp's tubes are loaded below 3000 ohms, distortion will rise. If loaded above that, its power will decrease as will its distortion.
The feedback allows the amp to behave as a voltage source. George has it wrong; the amp can make double the power into 4 ohms as it does into 8 because voltage sources do that (this is by definition). The deal is, the 4 ohm power is the maximum power for which the amp is rated and you have to be on the 4 ohm tap. If the impedance then rises to 8 ohms, the amp will make 1/2 of its output power. Its a bit confusing, because tube amps accomplish the task of being a voltage source in a way that is opposite of how solid state amps do it.
The issues are the same with an OTL, but of course no transformer is (usually) involved. Instead the tubes see the load directly.
@bifwynne I run into that too- we make OTLs as you know, but there are speakers out there that on paper would seem to be too difficult a load, but in practice work out just fine with our amps. So your experience does not surprise me in the least.
Feedback is helping you out here, and my surmise is that most of the speaker impedance curve is actually higher than the dips in the bass (the bass region also has peaks BTW). That's a pretty simple explanation for why this is working for you.
Quite often the 4 ohm tap on an output transformer sacrifices some performance- in some cases you can lose an octave of bandwidth off the bottom just by going from the 8 ohm tap to the 4 ohm tap. So it can be a mixed bag in the real world (as opposed to the math world of theory).
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