LSK pre - BAF 2013

Well, I was somewhat mistaken above regarding "no other changes". You will need to adjust the Resistors driving the gate of the cascode transistors for a slightly higher voltage. Where N.P. has 18V you will need about 5 more Volts there. You can get that by lowering the Rs on each rail or raising the Rs in the middle. I don't have a pic of the schez or I'd give the ref des for the Rs. It should be simple to calculate and get close. :D
 
...You will need to adjust the Resistors driving the gate of the cascode transistors...
Exactly - current supply resistors need changing in that case too. With changes shown in the sch. below I got about 28V_peak of clean swing at the output (I didn't dare to go higher since the J74's Vds reached 29V). The current through R2/R11 (1K) was 16 mA (about 6mA through JFETs and 10mA through BJTs).
 

Attachments

  • lskprehg1.gif
    lskprehg1.gif
    7.2 KB · Views: 5,745
Antoinel, check this pdf http://www.circuitdiy.org/Datasheets/SKU17-1.pdf
Small signal devices don't have complementary, but K69/J19
Thank you massimo. This SIT pair will broaden the use scope of the circuit presented by Mr. Pass at BAF 2013. A complementary folded cascode SITs may have a lower Zo than that of analogous JFETs, and thus save an additional output buffer if it is low enough.

Feedback from the output of the Pass circuit to the gates of its FE may fit the practice of Schade or Pass feedback. Consequences are a lower voltage gain, but with a new triode-like characteristics if desired.
 
Exactly - current supply resistors need changing in that case too. With changes shown in the sch. below I got about 28V_peak of clean swing at the output (I didn't dare to go higher since the J74's Vds reached 29V). The current through R2/R11 (1K) was 16 mA (about 6mA through JFETs and 10mA through BJTs).

Do you need resistors on the bases of the BJTs for stability, or is that not a problem in this circuit?