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Re: srpp or cathode follower-differences obesrved-

Posted by Quest on March 31, 2000 at 08:29:12:
Hi,
First off I would like to correct you for the several notions:
(1) SRPP (aka "Shunt Regulated Push-Pull") is not a Mu-stage. They operate in a slightly different manner. Although they seems to operate in a somewhat similar topologies, current-control-wise Mu stage is somewhat closer to a constant current mode.
(2) While some people see the upper half of an SRPP/Mu-stage as a current regulator, others like Thorsten looks at it as a cathode follower stage. While such topologies has it's merits of high input impedance and extremely low output impedance, high PSRR, high gain and so on. There are things such as high-order distortion yet to be dealt with.

(3) A CF(aka "Cathode Follower") offers < 1 gain. In other words it will require an additional gain stage before it in order to make it at least a unity gain. By itself CF stage offers no gain but loss.
(2) A CF stage can sometimes be perceived with feedbacks.
(3) CF stage offers high current, low output impedance driving capability.
(4) CF stage may not be linear throughout it's useable bandwidth.
Look: To me low output Z may seems appealing to many one of us but realizing that there's so much compromise involving when using these topologies leaves me little to be desired. While CF stage can be "tricked" into better linearity over it's usable bandwidth, SRPP/Mu stage is more difficult to obtain satisfying results (IMHO). They usually sounded diffused(not focused) and so on, despite their test figures looks good on the paper.
If you have the guts to do so try using conventional plate-out (Anode load) topology with a radical approach. You'll be surprised how much better they sound in most applications if applied properly.
Good luck!
Quest