MC352 into varying-load speaker?

I may be able answer at least one of those questions, Sean... I believe Ron here is Ron Cornelius, present Product Manager of McIntosh Labs and de facto spokesman for the company.

Sean,

On the 4 to 1 point. If the amp is terminated at 2.3 ohms before the autoformer and the autoformer has taps for 2,4, and 8 ohms, the autoformer does not have a very high matching ratio. The 2.3 ohm point is where the output stage is most linear and needs the least feedback for maximum performance. This is not so much of an issue with the autoformer but would be without it as there is not a lot of 2.3 ohm speakers.
I did not say that a pre amp has phase shift but the audio-taper pot usually does. Fully balanced designs can avoid this but fully balanced volume controls are complex.
Yes the actual power of an amp is the main factor in controlling bass. 10 feet of speaker wire will usually swamp most dampening factor specs. If the autoformer limited the output of a Mc amp they would not put out high power but they obviously do. A properly designed autoformer will pass all of the watts. Our MC1201 amp is rated at 1200 watts. It will sine wave about 3000 when a two ohm load is on the 8 ohm taps. On a ten millisecond tone burst under the same load it will swing 5000 watts. This is a lot of power. If one is aggressive with this amount of power we have seen voice coils pulled off drivers and the solder melted on crossover boards to where the parts fell off. The autoformer does not limit the amp's output.
McIntosh amps will roll off above 100 KHz by design. If an amp starts to pick up very high frequencies say from induction on the speaker wires this will get into the feedback network and may cause ultrasonic activity. Output transistors do not like very high power at very high frequencies. This is why amps are protected with coils or caps on the output stage.
In explaining the McIntosh engineering philosophy I am only responding to this thread. Most high end audio products are well designed and many companies other than McIntosh make fine amplifiers. The autoformer, Sentry Monitor, and Power Guard are unique to the McIntosh design and have tangible advantages all at a cost of course.
Thanks again,
Ron-C

PS- Yes I work for McIntosh and have various titles my favorite though is Historical Advisor. Now about that MC60..

Ron: I appreciate your responses. While we could continue down this path for quite some time, i'm glad that you've at least taken the time to share what you did with us. It is enlightening to know that there are still manufacturers around that don't have much to hide and are willing to discuss the design decisions and technology that went into their products. It is obvious that the 1201 is built VERY sturdily and can pass a lot of current. I do have further questions that i'd like to ask you about this and other Mac designs, but i think that you've been quite gracious with what you have provided so far.

With that in mind, i'd like to pass on some further observations that are slightly off the subject, but i think need attention brought to them. Given our "basic agreement" on most points after clarification, i don't think that you'll disagree with the points that i'm going to make. I could be wrong though : )

"Yes the actual power of an amp is the main factor in controlling bass. 10 feet of speaker wire will usually swamp most dampening factor specs."

I agree with this statement and have stated so in previous amplifier / speaker cable / speaker related threads. This has to do with the fact that most speaker cables are very poorly designed and present such a high nominal impedance to the amp. Length of speaker cables isn't nearly as critical or detrimental to the amplifier / speaker interface IF the speaker cables themselves are of a very low nominal impedance. In this regards, and i know that he's speaking on his own and not for Mac, i disagree with the comments that Roger Russell has posted on his website to a very great extent.

"If an amp starts to pick up very high frequencies say from induction on the speaker wires this will get into the feedback network and may cause ultrasonic activity."

This further proves the points that i've tried to make in this specific post and other threads. Just one more reason to avoid speaker cables that are inductive in nature. That inductance is also what is responsible for the higher than desired nominal impedance of the speaker cable. Chalk another one up for low inductance, low impedance speaker cables. That is, so long as they are properly terminated with an impedance compensation network : ) Sean
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Thanks Ron for the explanations! Cool hearing about the details involved. Arthur

I have read this complete thread and am very intersted as I also own a 352. I have done my own experiments with a couple of signal generators and an oscilloscope. Simply, what I found was amazing. The waveform or beat harmonics of the two signal generators did not change all the way up to where it was so loud that the low frequencys shook the walls. The various wave forms varied only in amplitude and never in shape. The 352 did not change its face, not one bit. Probably not to good on the speakers but overall a good experiment. (I wore hearing protection) Last but not least, if there is ever a tornado around here, I am running to hold on to the Mc. That puppy wont budge!

-Mark