McIntosh Amp Ratings

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.

Cheers,

David

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...