[Otis]

Hi guys, just wondering if anyone knows what motivated SS amps desigeners to drop the quasi-complementary dsign in the early 70's?

Was it economics, the quest for more Class A power output, better sound or what?

Philosophically, given the choices today, how does one decide what layout is best?

Otis

[avahifi]

My guess is that good matching NPN and and PNP output transistors were not available then, and it was hard to get good DC centerline stability under all conditions (heavy DC centerline offset and fried woofers was common).

Note that now a good design can have excellent DC centerline stability.  Case in point; all AVA OmegaStar solid state amps do not even need or have DC centerline adjustment trim pots. And that is with direct coupled output circuits.

Frank Van Alstine

[modular747]

My guess is that good matching NPN and and PNP output transistors were not available then, and it was hard to get good DC centerline stability under all conditions (heavy DC centerline offset and fried woofers was common).

Frank Van Alstine

There has been some revival of "quasi-complimentary" output stages.  Purportedly, NPN transistors have "better" linearity characteristics than PNPs, which aren't really complimentary to NPNs. One ultra high end (priced) manufacturer - Edge - uses this output topology.  Edge amps are a favorite of TAS.  For what it's worth, I saw a review (Stereophile, July 2004) of the Edge NL-12 ($15.5K and 3rd from their top) which included measurements  that were unimpressive, though the reviewer loved the sound.