Some of the DIYAudio fans have built this version of the 4P1L with great success. There are several upgrades that can be easily implemented to improve this. I haven’t tried this myself, but my recent experience with the Gen3 and the 01 preamp gen2, I think are worth trying:
- Replace the gyrator FET for a cascoded pair (M2 and M4 below) to improve PSR
- Replace voltage reference by a cascoded LND150 for better HF and PSR response
- Optimise the LF pole of the gyrator load by increasing R4 to 4.7 MΩ and reduce C1 to 220nF
- Bias 4P1L to about 30mA. This will reduce distortion
Hope this is useful
Ale
Accidentally,
while you were posting this Gyrator update, I tried to implement -starting from the JFET cascoded 26 Gyrator you published- something pretty similar (as above) except that a J310 is used instead of your M4 (DN2540).
It seems to work, but as I do not have any further measurement equipment at hand …. would you mind to comment why you selected as M4 a DN2540 instead of another JFET?
Kind regards,
Ulrich
Simply because I have many of them in stock. I think J310 should be a good choice in the lower position. Would be interested in your comments on how it sounds though.
Fine & thanks for your reply!
I’m not sure the comparability of my (future) comment, as I’m going to use the 4P1L as the first stage of a hybrid amp I’m on.
2nd stage will be 2SK82 based, one of the few SITs featuring a triode-like behavior.
My current first stage misses a little gain (Mu 5.7) and due to your constant posting I got some of the 4P1Ls; so I’m keen to give that DH(T/P) a try. Maybe later also as a pre.
Ulrich
If 4P1L is used as a driver, then don’t starve the filaments and use them in full tilt as needed. Either in parallel or serial mode. I’d recommend serial filaments as driver to ensure you have a smaller resistor in filament bias. Good luck and keep me posted!