Shunt Feedback - effect on input impedance

[gingertube]

Konnichwa Guys,

Thanks for the above. I also sat down and read thru' the entire "Partial Feedback" thread over the weekend. Also grabbed a copy of the Citation II circuit and had a good long look and reread the RDH section on feedback.

KYC 's sig. there says "There are two types of people in the world - those who get it and those who don't".

I'm more of the view that there are three (3) types of people in the world - those who can count and those who can't.

I don't get it ALL but I'm learning.

What I'm looking for is a direction to mod "bog standard" Menno Vandervenne amps, the 12AU7 common cathode amp - direct coupled concertina phase splitter and 2 pairs of "Winged C" Svetlana EL34s (Ultralinear Mode) with PAT 4006 (Raa=2100 Ohms to 5 Ohm ).

I've tried global feedback on this and other Class AB1 UL PP amps - with various quality output transformers and in EVERY instance where I've "tuned" global feedback for sound I've arrived at 5, 6 or 7dB of global feedback.

Anymore kills imaging.

Thanks again,
Ian

[jlsem]

We have already observed that the various theories which include the particular electron as key building blocks fail to explain reality sufficiently, they leave holes in realms usually justly called esotheric, but if a theory is reliable only in general midfield but not under extreme conditions the theory is in my view worse than admitting ignorance, because it has you reacting to a fundamental misunderstanding of the facts.

Am I to understand that electrons are imaginary because they don't help explain the imaginary?

John

[ThorstenL]

Konnichwa

Originally posted by gingertube
What I'm looking for is a direction to mod "bog standard" Menno Vandervenne amps, the 12AU7 common cathode amp - direct coupled concertina phase splitter and 2 pairs of "Winged C" Svetlana EL34s (Ultralinear Mode) with PAT 4006 (Raa=2100 Ohms to 5 Ohm ).

This circuit is poorely suited to sensible application of negative feedback, other than directly around the output valves by means of additional transformer windings.

Due to the nature of the circuit feedback from the output valves anodes to either Output Valves grids and/or anywhere else in the circuit is not applicable.

So you are limited to a global loop, no matter how problematic this becomes. The other option would be to completely re-design the Amplifier with a different driver circuit.

One option keeping the current layout might be a FET/12AU7 differential cascode with feedback from the anodes of the output stage to the source lines of the FETS....

Sayonara