AudiogoN Forums: How do autotransformers affect sound?

How do autotransformers affect sound?

Just wondering, I've noticed many of the McIntosh amps have autotransformers.
1) Why have an autotransformer on a solid state amp? Is it because it gets around designing for different current draws from different speaker impedances?
2) For tubes amps it makes sense I guess. The Mcintosh tube amps can be paired to various different speakers even those with impedeances of 2 ohms (or anything between 1 and 16 ohms as McIntosh touts). Is the only reason many other tube amp designers don't do this because the autotramsformer is another component in the signal path? What is the trade off? I mean why not hook up a very nice tube amp through an autotransformer such as the Speltz one and use your favorite pair of low-impedance low efficiency speakers? Why rule all those out if there's a simple solution as an autotransformer.

As an example I'm wonder if I could hook up an MC2275 (100 watt tube amp) to my Aerial 7Bs (drops to 4 ohms in the bass region) and get good performance.

One thing I noticed in auditioning the Mcintosh integrateds the 6900 had smoother highs than the 6500 which I've heard was due to the autotransformer (hand-wound!).

I'm think about picking up an MC2275 or an MC252/402. I want to try tubes but don't want to change speakers right now.

regards, David

Wireless200 (Threads | Answers | This Thread)

04-13-08

Responses (1-24 of 24)

Click title to read one, or click date to read all below it.

04-13-08 Are they autotransformers? i thought they were bifilar-wound ... Joeylawn36111

04-13-08 This is only my 2 cents worth, but in listening to many of t ... Sid42

04-13-08 An autotransformer (as used by mcintosh) allows the amp to d ... Eldartford

04-13-08 the big tradeoff is cost. and weight. which is the same as ... Kirkus

04-14-08 Distortion. transformers are notoriously non-linear devices. ... Shadorne

04-14-08 Its a fact that when you ask a transistor amp to make more c ... Atmasphere

04-14-08 Atmasphere...interesting. however it seems to me that this l ... Eldartford

04-14-08 I would imagine that most high quality ss amps can maintain ... Unsound

04-14-08 Atmasphere -- the capacitance multiplication you talk about, ... Mabonn

04-14-08 Atmasphere...just in case you don't have enough questions ye ... Eldartford

04-14-08 I read a good explanation on mac's autoformers from someone ... Onemug

04-14-08 Eldartford, the impedance relationship between the output st ... Kirkus

04-14-08 Kirkus...thanks! Eldartford

04-14-08 Onemug and atmasphere are right on. the impedance is indeed ... Aball

04-15-08 Arthur, just a couple of minor clarifications . . . bifilar ... Kirkus

04-15-08 The turns ratio of the mac autoformers, like the zero and ou ... Atmasphere

04-15-08 Interesting reading on the obvious merits of adding an autot ... Shadorne

04-15-08 Shadorne...i believe that transformers usually have feedback ... Eldartford

04-15-08 Kirkus - autotransformers can indeed be bifilar wound if you ... Aball

04-16-08 good point and you can improve the linearity through feedba ... Shadorne

04-16-08 Wow, really interesting thread. atmasphere, i get the impre ... Kirkus

04-16-08: Atmasphere

what you're describing is simply the tendency of certain topologies to present non-linear loads to their preceding stages. If this is the case, then how is this substantially different than a tube output stage running in class A2 or AB2 whereby grid current becomes significant for part of the cycle?

How its different is that the domain is more that of current than voltage and that there is a substantial variable capacitive issue intertwined. In a tube, once you get to the class A2/AB2 window, you are dealing with grid current but the capacitance is not really a variable. Semiconductors present you with this issue regardless of class of operation.

Eldartford, its true that solid state amps will be smoother sounding at higher impedance but the old Macs that we were talking about were solving a trickier issue of limited rail and breakdown voltages as well. The autoformers were a solution for that, to get the target performance of the amp inside the limits of the available devices. With the newer Macs this is certainly not the case. If you were to load one of those early Mac amps with a low impedance, I will guarantee that the results will not be as satisfying as with a higher impedance.
Atmasphere (Threads | Answers | This Thread)

04-17-08 Kirkus - the way i know "interleaving" is by inter ... Aball

04-17-08 Arthur, fwiw the zero (zeroimpedance.com) has a very low tur ... Atmasphere