"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp)
View all posts by Ale Moglia
2 thoughts on “26 DHT preamp Gen3”
Dear Ale,
first of all thank you very much for sharing with us your great achievements reg. gyrator/CCS. I’am just starting to build one with JBF 862. Only on detail is not clear for me concerning calculating adjR of JFET. Apparently it is not referenced to Vgs like with Mosfets but somewhere between gm, mu, Ri ? 🙂
Thank you in advance for your advise and enjoy the weekend with your family, wine and music.
Goetz
Hi Goetz,
Rum (or R7) depends on J1’s transconductance for optimal performance. For maximum output transfer ideally should be 1/gm. Gm of BF862 is about 45mS at best case. That’s 22R. However, the gm of the JFET at low VDS levels is less than that. I found 470R to 1K5 to work (and measure) well.
Dear Ale,
first of all thank you very much for sharing with us your great achievements reg. gyrator/CCS. I’am just starting to build one with JBF 862. Only on detail is not clear for me concerning calculating adjR of JFET. Apparently it is not referenced to Vgs like with Mosfets but somewhere between gm, mu, Ri ? 🙂
Thank you in advance for your advise and enjoy the weekend with your family, wine and music.
Goetz
Hi Goetz,
Rum (or R7) depends on J1’s transconductance for optimal performance. For maximum output transfer ideally should be 1/gm. Gm of BF862 is about 45mS at best case. That’s 22R. However, the gm of the JFET at low VDS levels is less than that. I found 470R to 1K5 to work (and measure) well.