JFET-only Circlotrons without negative feedback

[Hennady Kovalsky]

This is serious question since im beginner. I have been reading about different feedback and what they do to sound.
I used to think that negative feedback is all evil since amplifiers that use it does not generally sound too "open, flowing, organic, breathing" for me..

But then i encountered 3 amplifier, rh84 tube amplifier that uses littlebit local feedback? Threshold t200 that uses minimal feedback, and luxman l58a that uses Duobeta feedback system.:
( explanation of duobeta: https://audiokarma.org/forums/index.php?threads/luxmans-duo-beta-amps.59555/ )

All those amplifiers uses feedback and goes into catgory of "open flowing organic sound"

the circuit from the starttopic would not be hindered by common-mode stabilization of the input stage, this will be a controlled shallow NFB that will align the halves of the sinusoids to control the mosfets in the output stage,
Otherwise, the sound will be determined by the constant selection of resistor values at the sources of the input JFets, which will need to be adjusted depending on the “weather season” outside the window and whether the neighbors’ vacuum cleaner is running.

 

[jpatay]

Figured I would snag a few of these while they’re readily available. I’m in between workshops right now so they’ll have to wait a few more months. But I’m very excited about the possibilities.

You need to read messages No. 127, 180, 199, 200 again... We got minimal distortion at a current of 1 A. We will have to install a thermal sensor, otherwise the current will increase very slowly. The supply voltage of the output stage is sufficient at 27 V. Good luck to you.

 

[jpatay]

Final circuit using КП903 jfet and 1T806 germanium transistors. With a total current of 320 mA, the minimum THD was 0.051412%. Power 1 W.
When the current is increased to 400 mA, the third harmonic increases.

 

[Svjatoslav]

Of course, we mean quiescent current.

 

[jwjarch]

You need to read messages No. 127, 180, 199, 200 again... We got minimal distortion at a current of 1 A. We will have to install a thermal sensor, otherwise the current will increase very slowly. The supply voltage of the output stage is sufficient at 27 V. Good luck to you.

Thanks jpatay! I’ve been studying those posts a lot the last few weeks. I’ll be sore to post when I have some progress.

 

[jpatay]

I’ve been studying those posts a lot the last few weeks. I’ll be sore to post when I have some progress.

It's been three years since you became interested in this topic.

 

[jpatay]

the circuit from the starttopic would not be hindered by common-mode stabilization of the input stage, this will be a controlled shallow NFB that will align the halves of the sinusoids to control the mosfets in the output stage,
Otherwise, the sound will be determined by the constant selection of resistor values at the sources of the input JFets, which will need to be adjusted depending on the “weather season” outside the window and whether the neighbors’ vacuum cleaner is running.

I still don't understand what you meant. Could you give us a more detailed answer? Дякую.