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In Reply to: RE: If that is what you want to know then.... posted by Jim Austin on May 16, 2009 at 06:25:51
Disagree with doodlebug's assessment completely. For 20 years, from 1950 to 1970, the only two power amp topologies used were the Williamson (and slight variations) and the McIntosh. The Mac has yet to be copied, even though the patents have long since expired.
By using extra windings in the output transformer they were able to get enough local feedback to achieve unity gain. (May as well as used cathode followers instead!). Then they had to get extra gain to run the output stage. So they added an extra driver stage that had positive feedback ("bootstrapping"). In my book, the whole thing was kind of a big mess requiring a horrendously complex circuit *and* output transformer (which is probably why nobody else has touched it with a ten foot pole), but it worked, measured great, sounded pretty damned good, and was the foundation for a company that has truly and justifiably become a legend.
It was in the '70s and '80s that the real innovations started showing up. Between ARC's fully balanced designs and the resurrection of Valley and Wallman's "cascode" (thanks for the memory jog, Allen), a whole new generation of circuits was born (including the so-called "mu-follower" variation on the cascode).
Go look at a Vacuum State Schematic or any of the classic ARC power amps. No relationship to either Williamson nor McIntosh in sight.
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