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
