JFET-only Circlotrons without negative feedback.

There is a desire to make a powerful amplifier exclusively on JFET.
Without negative feedback.
Tested circuit at low power is already available.
There is now a powerful MOSFET output scheme.
The next step - a powerful circuit Si-C JFET.

Related topic:
JFET-only Headphone Amp "Circlotron КП903B".
 

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How does it perform?


Wide question. It works very stably.
Even at low rest currents (50 mA) there is no "stair".

In addition, the small JFET transistors in this switching circuit turned out to be very resistant to breakdown voltage.
Which allows you to increase the supply voltage.
 
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Well amplifiers should work stably, but how does it perform?

When the amplifier was operating at medium power for one hour, the output stage current increased from 100 mA to 160 mA. It was on a small radiator. Now I'll see how it will be on large radiators and later I will write the result.
The preliminary part is very stable. When the amplifier is turned on, the shutters are +3.85 V, and when warming up, it is +3.81 V. This is very good.
 
Hi

Where could we found or replace VT1 and VT2 ?

Thanks

Hi!
Any low-power n-channel JFET with an initial current greater than 8-10 mA can be used as VT1. As BT2 - with an initial current of 1.5-5 mA.
It is important that the voltage is drain-source VT2 was on the verge of crossing the triode to pentode characteristics. As outlined in the figure.
The same goes for relationships VT3-VT4 and VT5-VT6. In both shoulders to equal or close.
 

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There is a desire to make a powerful amplifier exclusively on JFET.
Without negative feedback.
Tested circuit at low power is already available.
There is now a powerful MOSFET output scheme.
The next step - a powerful circuit Si-C JFET.

Dear Svjatoslav!
great name!
emiter/source resistors are suspected for sound quality degeneration, please refer this great thread: Emitter resistor in HexFet OPS
but I think that mostly in gnfb amps, not open looped like yours.
Do you think that ommiting 0.1 Ohm res (I know that they are very small valued) is possible in your circuit?
Would you do the test what will be idle current change after shorting them?
Slava!