McIntosh Amp Ratings

Does the Autoformer design of Mc amps allow them to rate their amps at higher watts than competative designs? They are one of the few using this design so I would think if it really was great, others would copy.

Is a 250 watt Mc actually comparable to a 125 watt other amp (which would double to 250 @ 4ohm) since most amps are rated at 8ohms?

Don't get me wrong. I own some Mc gear and love it but have wondered if they have clung to this for the spec wars.
Like any amp with an output transformer (or autotransformer) power delivery will be the same into any load for which there is an output tap. So the "double down" rule does not apply, but neither does the "divide-by-two) rule when you go to an 8 ohm speaker.
An interesting observation I had made about mcintosh specs which I believe a one of the contributing factors to making them more universal and tube sounding is partially the autoformer deal, but also they have very low damping factor in comparison to esoteric Solid state amps… Most of them are like 100 to 150… Big amps with tons of juice that everybody seems to get off on have 600 or 2000 damping factor, to me these amps are mostly toughted as " More defined bass" or "Tighter" but to me they sound more constipated, and many times less organic than most Mcintosh designs.

Also being the damping factor is so low on them it seems that’s really the one Spec that matches up to most tube designs, which might be part of the key they seem to be more of that musical and accepted sound. I don't really know, but just an observation.
I understand McInotsh amps have a certain following, but Undertow, what you're saying makes little or no sense. Other amps sound constipated? Wow. That totally contradicts my observation, which is McIntosh amps sound fine with an easy load speakers. When you pair their amps with a difficult to drive speakers that have some impedance curves, or what have you, smaller McIntosh amps sound constipated. Actually any Mac amp up to MC501 monoblocks can not really be paired with any challenging load. You need to at least start with MC501 monoblocks for such task. And the fact that McIntosh amps don't double down doesn't help either. For example, with B&W 803D or even N803, MC402 sounds OK on lower levels, but the louder you get, the more obvious the dynamic restrictions seem.

I mean I do understand if you like McIntosh sound. That is totally up to you. But deeming McIntosh amps as above anything else is a bit of an overstatement, to say the least.
Hi, Mc-602 owner,
Yes Auto formers will restrict the dynamics as you reach the end of the power band. It's a trade off between clipping and max power.

McIntosh amps don't clip. Protecting one's speakers from damage!

So the real question is how much power does I need to achieve the volume level desired.

Fundamental rule is to double volume it takes 10 times the power.

Meaning if you like to listen to soft levels 10 watts is average, double volume is 100 watts, to double again 1,000 watts. As you can see it does not take that much volume to max out a 1,000 watt amp. How much air do you want to move? This is where the term headroom comes into being. I say you should have at least one level double volume of headroom.
My McIntosh MC-602 will put out 600 watts and not even get hot. At 60 watts I move a lot of air and still have 540 watts to play with.

Another factor one should consider when choosing a amp. HEAT will destroy it over time. McIntosh amps have a long history of running cool. Just look at all of the used 40-50 year old amps for sale on Audiogon still getting good money. With McIntosh if you keep it long enough you can sell it for more than the original price.... How many other Mfg. can claim this ?????

The last point I will make is Big amps have so much more detail @ one half watt output. I love my MC-602
My 501's drive a very difficult load in Thiel 3.6, low impendance factor but fairly stable curve, with no problem in a room probably too large for the speakers. They never run out of gas, fill the room with music and I usually crank them!
Seems to me that there's a fair amount of mis-information being batted around, here. The use of autoformers on the output end of an amp is used to ensure that there is the best transfer of power from the amp to the speakers when the speaker load is attached to the most appropriate tap for that speaker's impedance curve.

This is the same electronic principle as found in matching a Moving Coil cart via a Step Up transformer into a phono preamp, and is the basis for any matching of 2 devices where low level signals need to passed with minimum loss of energy.

If you compare the output specs into 2,4, or 8 ohms for the solid state Mac amps that do and do not have output autoformers, you'll see that the specs for the ones with autoformers will quote the same power output at all impedances. The amps without autoformers will show rising power output power as the impedance goes down. The thing here is that the non-autoformer will tend to get hotter driving lower impedance loads since there is a larger impedance mismatch. Think of that heat as power that didn't get to your speakers from that mismatch.

BTW, Mac amps are not _normally_ driven into clipping due to the Power Guard circuit, which limits output drive as maximum power is approached. You can stil abuse the amp if you really want to but I can tell you from direct experience that this feature has saved many a set of speakers in professional situations - not to mention drunken college parties.


Other manufacturers may not copy because it adds a lot to the cost and a lot to the weight plus there is an art to winding them and Mac has been at it for over 50 yrs.

If you compare the sound quantity (not quality, that's up to you), of an AF Mac with 250 watts to say an older Krell with 125, the Krell will play louder on 2 ohm speakers, the same on 4 ohm, and not as loud on 8 ohms. That was one of Macs selling points: You buy a 250 watt amp, you get a 250 watt amp. Long ago and maybe not to far in the future there were some 16 ohm speakers. Mac used to have 16 ohm taps, (I think their newer 275's still do), the Krell would put out around 63 watts on them. These are only 3db differences. As Horses2harleys noted, if you want to play twice as loud as 125 will give you, you'll need 1250 watts

All the others here have made great points on why AF's are a good thing. My fave is that it allows the output stage to run at its most linear point. Linear is a good thing.

There is no perfect amp. It just doesn't exist. When you hook up any amp to a resistor, it may test very well. Speakers aren't resistors. I like the path that Mac has chose.
The Autoformer doubles down and halves up depending on what terminals you run the speakers off.

I explained this in another thread for those who are interested...
Most of these posts are right on. Although I think the doubling up and halving down isn't exact with Autoformers due to coupling effects. Theoretically, yes, but in reality, no. Take a look at the Stereophile measurements of the MC501 and you'll see what I mean. For example, peak output power was 1000W with 4 Ohms taps driving a 2 Ohm load.

Incidentally, check out also how the 501 only has +-0.1dB modulation with the reactive loudspeaker load. The 8 Ohm tap has a damping factor of 100 and the -3dB is at a high 120kHz.

Undertow - I made a similar observation as you about damping factor. Some tube amps really have wonderful bass - perhaps not the most "potent" but very natural. John Atkinson and Roy Gregory also made this oberservation. Many forget that damping factor is related to both the frequencies of the musical signal and to frequency-dependant reactances. So an amp's ability to handle phase shifts is the real deciding factor for how well controlled the bass is or not. Besides, a driver is going to have its own mechanical and electrical impedances, especially a bass driver, so its own decay time will impose real limitations. From what I have seen, these limits basically render any DF above 50 a wash.

But we really knew all this already - particularly if you agree that global negative feedback is bad or that parallelling a bunch of BJTs (or even worse, MOSFETs) is not the best way of keeping a signal pure and unadulterated.

I guess that is the best way to describe..Natural, I feel much more Power in bass from Tube amps.. And have also from Mcintosh amps, but to be fair most of the Mcintosh amps I have heard were using Mcintosh preamps with Attenuation of the Bass knob or loudness control..But still they have a very full midrange and vocals, I have never really bought into the Mosfet argument either, I have owned several and they never quite did it for me.. I believe all Mcintosh are Bi-polar correct? I have found them more natural devices in most amps I have owned, but thats a whole other argument, and who cares anyway?

I don't own mcintosh and I do not necessarily defend them as being the best, just interesting and how I feel that they do give more of a Tube character to loads driven than that of most extreme cost SS amps. Again it was just an observation being that Mcintosh amps at the very hi price points are some of if not the only Solid state amps with super low damping factor.

You're spot on about the McIntosh can deliver more power at lower impedances but it, like all other amplifiers, is limited. The Mac is probably more conservative as part of their design intent is to minimize heat generated to prolong life.

also, Autoformers kill damping factor, which probably explains why traditional output designs that offer better control of the woofers are prefered by some.

other companies don't use an autoformer because mcintosh has a patent on it.

I have owned quite a few Mac amps.  My favoirte was the MC-2300, which did not have an autoformer.  With regard to Macs power rating CONSERATIVE is their practice.  The MC-2300 could put out nearly 500 watts into an 8 ohm load though rated at 300 per side.  Strapped in mono, power deliery was astronamical, as it would easliy better 1500 watts.  I know beacuse I still have the bench sheet from my personal amp tested during a Mac clinic.

Further, this amps was factory rated to drive a half ohm load.  Not many compaines have that type of confidence in their products ability to drive loads.  Damping factor was always stated with low numbers.  This is because a damping factor of more than 20, was thought to be inaudible and ridiculous according the Mac engineers of the day, so that was all they ever tested for.  Any Mac amp when tested will easily give you a high damping factor.

Mac specs are always quoted as "worst case".  Who else does that? No one I can think of..

i've read before that most mac amps would put out about 1/3 more watts then the rated output. 300 watt per chanell amp would put out 400 watts per chanell. any comments on this?
It depends on how the wattage is measured or more specifically the distortion level % at +/- dB. I have a pair of MC2200s and according to the performance graph shown in the owners manual, the distortion level at 200 wpc is basically a non issue. At 270 wpc the distortion is just about the level where most other manufacturers advertise their continuous power ratings. On the amp itself, it says 200 wpc minimum power rating. So I guess in this case the 1/3 higher power rating is about right.