J-fet Zen Srpp ???

[Circlomanen]

I came to think of this today.

An externally hosted image should be here but it was not working when we last tested it.

Of course cascode moddulation can be implemented. would it work?
As its drawn it has a ultralinear feedback arrangement.

 

[Nelson Pass]

I believe it will work very well. I have a similar schematic which I
have yet to build.

 

[kekso22]

The circuit should have much more gain then ZEN9?
Do you have modelled it with SPICE?

Regards

 

[Circlomanen]

Thank you Mr Pass! Looking forward to it!


kekso22: I have not spiced it. I dont know how to. I dont know if it has more gain than Zen v9, but its a way to make a simple pushpull circuit.
I just like the SRPP circuit Its simple and elegant.

 

[Circlomanen]

I think R10 should be a constant current source. It should work a lot better with a stable voltage accros R11.

 

[tschrama]

Or a cap around R11


Very cool circuit Circlomanen

 

[Circlomanen]

Or a cap around R11

Yes, thats one simple solution. Thanks!

Very cool circuit Circlomanen

Im glad you liked it! Thanks one more time!

Johannes.

 

[Circlomanen]

An externally hosted image should be here but it was not working when we last tested it.

The preamp.

 

[Circlomanen]

I think that R8 and R4 should be 33 ohms or something similar.

 

[massimo]

The preamp

Some friends of mine years ago tried a Fet based SRPP circuit, using Japanese and European semi such as 2SK and BF type, but they found many problems.
The only "working" Fet/SRPP schematics I'm aware of has been published on the Japanese mag MJ.
The "secret" was the particular hi voltage Vfet used: 2SK79, made by Sony and non longer manufactured).
I understand you circuit is different, but I think it needs to be tested carefully.

 

[Circlomanen]

Some friends of mine years ago tried a Fet based SRPP circuit, using Japanese and European semi such as 2SK and BF type, but they found many problems.

Intressting!
Can you be a little more specific about what the problems where! I would be very greatful for some info about the all Fet SRPP, since im about to build something along these lines.
Johannes.

 

[Circlomanen]

I just tried to build one J-Fet SRPP preamp from used parts I had laying around. It did not work.As I said, the J-Fets were all used parts and might not work,I didnt match them. I might have done something wrong but I could not find any thing wrong by visual inspection. Some more testing is needed.

 

[Circlomanen]

I think I know what the problem is. Triods have RP and that works as a voltagedivider to set a stable DC midpoint. The Fets have a to small "RP" and to much gain to be stable at setting the DC midpoint.
I have to use a voltagedivider with resistors to set the DC.

An externally hosted image should be here but it was not working when we last tested it.

 

[massimo]

I think I know what the problem is. Triods have RP and that works as a voltagedivider to set a stable DC midpoint. The Fets have a to small "RP" and to much gain to be stable at setting the DC midpoint.

You find the answer by yourself. The problem my friends faced was due to the instabilty of the circuit continuosly drifting.
I do hope you find out the cure!

The Vfet 2SK79 arrangement was: V 60V, I about 1mA and, referred to your first schematics, R 1=1k, R4&R8=1.5k (selected for the Idss of the fets in use) R3=330ohm, Rload/in=1M, Rload/out=470k, Cout=4.7uF with 100ohm in series.

 

[Circlomanen]

The Vfet 2SK79 arrangement was: V 60V, I about 1mA and, referred to your first schematics, R 1=1k, R4&R8=1.5k (selected for the Idss of the fets in use) R3=330ohm, Rload/in=1M, Rload/out=470k, Cout=4.7uF with 100ohm in series.

Thank you Massimo!

Cheers Johannes.

 

[tonecat]

Satisfactory results appear to have been had with 2 JFETS without using a third device.

Wrenchclone appears to have had some success with JFET SRPP over in the analogue forum...

http://www.diyaudio.com/forums/showthread.php?postid=720494#post720494

There is also a JFET SRPP/MOSFET pre-amp at...

http://tkhifi.homepage.dk/foramp/forampfet.html

SRPP stages are noted subjectively for headroom and dynamics and are common in tube designs - very easy to set up with tubes and I have had favourable results with them.

 

[lineup]

Satisfactory results appear to have been had with 2 JFETS without using a third device.

Wrenchclone appears to have had some success with JFET SRPP over in the analogue forum...

http://www.diyaudio.com/forums/showthread.php?postid=720494#post720494

There is also a JFET SRPP/MOSFET pre-amp at...

http://tkhifi.homepage.dk/foramp/forampfet.html

SRPP stages are noted subjectively for headroom and dynamics and are common in tube designs - very easy to set up with tubes and I have had favourable results with them.

thanks, tonecat

I am about to investigate SRPP using JFET.

I will start my design & simulations using 2SK170BL.

Those links will become good reference material for my work.


Regards Lineup

 

[Nelson Pass]

I just tried to build one J-Fet SRPP preamp from used parts I had laying around. It did not work.As I said, the J-Fets were all used parts and might not work,I didnt match them. I might have done something wrong but I could not find any thing wrong by visual inspection. Some more testing is needed.

The issue would be DC stabilization. You can use feedback or refer
the current source to a midpoint DC reference value. Either works
fine.

 

[Telstar]

Would the semisouth jfets be suitable for a SRPP with enough gain (20-30dB)?

 

[StevenOH]

SemiSouth JFETs are well suited for SRPP. Use source resistors Rs and the shunt of the same value and as high value as you can (up to 1Ω) and of appropriate wattage. It will be good to have the shunt 0.1Ω higher, than the top counterpart. The gain of the stage will be ~2Rl/Rs.