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OTL (was Re: Good, vibration-free trannie is hard to find these days..)

Posted by John Harper on October 1, 2000 at 09:43:18:
>While OTL has it's merits of eliminating all the impedance matching shortfalls from using a transformer, by itself OTL has many of it's problem also.
>Things like output power greatly governed by the speaker load, low efficiency (about 1/20th to that of a typical AB1 tube pp amp). the need of very
>low plate impedance tubes, the tendency to oscillate(or parasitic oscillation), difficult to build and calibrate it right, the need of a big electrolytic
>capacitors acting as a coupling cap between speakers and the tube plates, need for NFB, etc.
Some of this is true but not all. Efficiency is low, but who cares.
You do need low impedance tubes, e.g. 6AS7/6080 or 6C33C. However
there is no need for coupling caps, nor NFB, nor are they difficult
to build or calibrate. The Circlotron design (as used by Atma-Sphere)
avoids nearly all of the folklore disadvantages of OTL.
John