Macintosh vs Pass labs

Know_talent, I read your post few times and I can't seem to understand it.

Though McIntosh autoformers deliver rated wattage at 2, 4 and 8 ohm terminals, they still double power as they go down. That is why people experience thermal overload when hooking up B&W's to the 8 ohm taps. The current draw heats up the unit and it shuts down.

Rated wattage for, let's say MC402, is 400w/ch. If this is what the amp delivers into 2, 4 and 8 ohms, how does it double down?

I've heard a 100w/ch McIntosh stereo amp in the store driving B&W N803 for about 40 seconds on a normal volume. Well, I wasn't the one who experience thermal overload. That McIntosh amp was. It just shut down. At the time I had at home a McCormack DNA-0.5 Deluxe, that was rated similarly to that McIntosh amp. I never had a problem driving the N803s with it. Granted, the speakers were underpowered by this amplifier, but it never stopped playing. That McIntosh amp simply gave up in a relatively short time. I call that unacceptable.

Now, your last paragraph, again is unclear, when you mention that a MC501 only delivers 250w/ch from its 4ohm posts into an 8ohm load....how's that? A speaker(i.e B&W 800 series) can have an impedance curve and go from 8ohms to 3ohms, depending on what's playing and how. So what good would the MC501 be?

I understand things like brand loyalty and I'm not bashing McIntosh amps. I think they're fine amps and there are certainly people with the right speakers with which these amps sound great, but, I guess I just don't understand all this autoformer principal and how it works(if it even does).

Audphile1...

The whole purpose of the autoformer is to create an ideal impedance match with the speaker being driven.

If you have a speaker that runs 8 ohms nominal impedance and run it off the 8 ohm terminals you'll get the 500W into 8 ohms, 1000W into 4 ohms and, for short excursions, 2000W into 2 ohms. Depending how much the impedance curve dips below 8 ohms will dictate how much extra current the amp is producing and the power sentry will shut it down when it senses too much heat.

Same thing again, but this time you instead hook up to the 4 ohm terminals. Now you're getting 500W into a 4 ohm load, 1000W into a 2 ohm load and 2000W into a 1 ohm load...though probably only for brief transients or the power sentry will shut things down do to thermal overload.
Notice how the amp doubles power as impedance is halved..
Conversely a 8 ohm load, when hooked to the 4 ohm terminals will be 250W, half the 500W rating.

Theoretically if you hooked up to the 2 ohm terminal you would generate 500W into a 2 ohm load, 1000W into a 1 ohm load and 2000W into a 0.5 ohm load...but I'm pretty sure the amp is not designed to handle such a difficult load???
A 4 ohm load would be 250W, while an 8 ohm load would be getting 125W.

The intent of the autoformer is to best match the nominal load of the speaker so the amp is not overheating with large impedance dips.

Think of a conventional amp with single output taps that is rated for 500W into 8 ohms, 1000W into 4 ohms and 2000 into 2 ohms. If you hook up a speaker to this amp that has nominal impedance of 4 ohms, with occasional dips into 2 ohm range you will obviously have an amp that is running quite hot!!! Now hook that same speaker up to the 4 ohm terminals of the autoformer and you'll have just 500W available at 4 ohms and 1000W into 2 ohms, but the amplifier will run much cooler and therefore last longer.
You could hook the speaker up to the 8 ohm terminals and get the 500W into 8 ohms, 1000W into 4.... but the heat would be so great that the power sentry would shut the amp down depending on how much time was spent in the lower impedance regions.

Call Chuck Hinton from McIntosh he might be able to explain it in simpler terms.

Know_talent, thank you for taking the time to explain.
I still don't think McIntosh are as universal of amplifiers as some other amps, but that's just me.
I won'd be calling McIntosh as I have no interest in their amplifiers. At least not right now. Your explanation is enough.