What is the "Schade"

[Bonsai]

Maybe an interesting note: What folk on diyAudio are calling "Schade feedback" really isn't. O. H. Schade's famous 1930 paper describes an entirely different form of feedback, applied in series with the input signal rather than in parallel. At some recent point in time it was misunderstood, and the misunderstanding has become entrenched. See Fig. 33 for the original.

All good fortune,
Chris

That’s an incredible paper given it was written in 1938 - lots of graphs etc. 👍👍

 

[6A3sUMMER]

jan.didden,

There is a resistor, DC to VHF frequencies from the output tube plate to the driver tube plate. That means the driver plate sees feedback all the way to DC, and it loads that driver plate all the way down to DC. A common way for many "Shade feedback", whether it is the original historic Schade or not.

There is only a capacitance in Miller Effect. There is no DC feedback from plate to grid, and no DC loading of the signal that comes to the output tube grid from the Driver tube.

Differences are small, but sometimes are real important to get an accurate analysis of that kind of topology.

 

[jan.didden]

You can dimension feedback all sorts of way, DC, AC, a combination, high pass, low pass, the sky is the limit.
What is absolutely the same is where the feedback is taken off and where it is applied.
That makes it the same.

Jan

 

[6A3sUMMER]

So a Williamson with 3 poles in the feedback loop from transformer secondary to the input tube cathode is the same as a two stage and two poles with the feedback loop from the transformer secondary to the input stage is the same thing?

Or if the concept of 3 stage versus 2 stages is an issue, is a 2 stage with one pole and all dc coupled called a Schade topology.