McIntosh and Autoformers. . .?

I really like the new Mcintosh gear. I currently have the MA6900 integrated and I'm upgrading to the MC2102 and C2200 tubed components. The MA6900 is basically the MC202 and C42 preamp in one box. The 402 is a step up in quality, but should be paired with a good Mcintosh preamp to get the most benefit. I really like the Mcintosh sound. it just works in my system. Full bodied, dynamic, great bass, clean, a bit of warmth. And they look really good. Your friend may be recommending the new gear because the older, or rather middle age Mcintosh gear is supposedly not as good. They recently brought back one of the original Mcintosh guys and he's been bringing the designs back up to the level of the early Mcintosh, but of course with new technology. The only problem with the autoformers is their weight. Ugh! Some say Mcintosh is good with B&W, but I like it with Tannoy speakers.

My experience is that I had and still use a MC7205 multi channel amp and I purchased a MC352 about a year ago. The 7205 always sounded good and I was satisfied with all but the power. So I stepped up to the 352 for the front end and WOW!!! What a difference, my understanding from discussions with McIntosh is that the Autoformer uses three "tap in" areas of the output transformer. This permits Mc to produce an amp that is a consistant 350 watts at 2-4-or 8 ohms. Rather than have one output you pick up in three areas which like having three individual output transformers. I don't understand why no other manufacturer hasn't picked up on this technology or a variation of that. I just can't say enough about Mc amps. I also use a MX134 pre/pro and my sincere belief is that I will always own at least Mc amps.

I own the 202 and use it with tyler ref moniters along with a mcintosh c37 pre, I feel its a great combo, plenty of punch, never bright, great detail. I would love to own a 352 or 402 but would get a hernia just moving it.

According to what I have read in the past, an autoformer is either a straightforward output transformer - albeit one with bifilar winding and multiple taps - or it's different in that it doesn't have a secondary coil, which makes it sound like an iron-cored inductor of sorts. Regardless, any type of output transformer is a rare thing for a solid-state amp, and the output of Macs so equipped is fully balanced rather than hot-and-ground. The point of having them at all, as far as I've been able to glean, is to present the amplifier output stage with a constant impedance to work with, optimizing linearity and power transfer, and also to block any potential DC at the outputs without having to resort to capacitor- or servo-coupling. Mac states that their autoformer models are fully balanced amplifiers, with the phase and anti-phase signal from either of the two duplicate amplification paths being combined at the output autoformer's bifilar windings in order to cancel noise and distortion common to both legs. Though Mac says the autoformer has wider bandwidth than the amplifier itself, audiophiles have theorized that its similarity to the output transformers used on typical tube amps gives these Mac models a superficially similar sound, compared to typical SS amps where the ouput stage is more directly coupled to the speakers. I hope someone with the technical knowledge comes along to shed a little more light on this question.

The autotransformer is a single winding coil with taps on a core of steel (generally). The taps allow impedance transformation by the ratio of turns being used. So one is able to connect, lets say, an output stage with output impedance of 1K ohms to an 8-ohm speaker with minimum loss. There are some losses and residual distortions associated with ATs. Hysteresis and eddy current losses define the core power losses and the core linearity will contribute a small amount (negligible in most cases), of distortion. This is generally only an issue at very low frequencies where the signal drive is often high and reactance is low therefore more current, therefore more volt-seconds are produced in the transformer driving the core closer to saturation.

An autotransformer does not block DC. As a matter of fact, residual DC on the output of an amplifier is detrimental to the AT operation as it will saturate the core. This residual DC creates constant flux in the core - then the dynamic AC output either adds or subtracts from this residual flux. When additive, if the flux goes above its knee limit (determined by the amount and type of steel in the core), then it saturates and the transformer then approaches a short circuit. Needless to say most amplifiers do not like short circuits. In balanced operation though, assuming the same residual DC from both circuit halves, the flux will cancel in the core so this I guess we could say that it blocks DC given the assumptions that the residual DC in each half is equal.

Even with the negatives of inserting another piece of iron in series with the signal, the advantages of an AT should outweigh the disadvantages. It is easier to design a power circuit with impedance higher than 4 or 8 ohms due to classic technology. Optimizing a design and living with the resultant impedance then adding a well designed AT should just about always be superior to designing a low output impedance stage using global feedback and all the other tricks of the amplifier trade. The AT just makes life easier on the output stage. The output transistors handle less current therefore produce less dynamic signal distortion due to changes in beta (gain) as more current is passed through them.

Most tube amplifiers incorporate an output transformer as part of their design due to it being virtually impossible to design classic tube output stages with low output impedance. So full transformers are used to effect the required impedance transformation. Assuming the output transformers are well designed for audio applications, I don't think the AT is necessary. However, the AT is almost mandatory for OTL amplifiers. And, it really makes a difference here. Listen to an Atma-shpere with the AT on a pair of Magnepans, or most any other high end speaker, and you will be willing sell your wife to buy one.