ProtoDAC TDA1387 X8 project

[hifinet]

Yes, the CAT SL1 seems to be very highly regarded. I had to look up the CAT SL1 preamp, and there is a diyA thread with apparently the correct schematic here. It's a mu follower. Where the 6DJ8 is used is more as a cathode follower, so I wouldn't think it contributes that much to the overall sound. Most of the sound being from the 12AX7 (and 12AU7), but I need to read the Morgan Jones circuit analysis.

I had built the SL1 before with modified tube power supply for the B+. Very musical with punchy bass. Original design is solid state power supply which I haven't tried yet. Maybe one day I will. There is PCB available on Taobao for both versions.

https://www.youtube.com/watch?v=SVlRRSrfzM4&t=75s

A discrete MOSFET regulated high voltage supply. I used Maida LM317 high voltage regulators on all my tube stuff. It is much simpler than the CAT discrete regulator, and there is a significant benefit to regulating the tube supplies. Highly recommended. Easy to put one together on a perf board. Since you don't want a widely variable supply (as in the original Maida circuit), just use fixed resistors for the voltage divider with a parallel trimmer. Online calculators available. Wire wound for the large value resistor makes the voltage more stable. I have used old TV horizontal transistors directly mounted to the metal chassis for high dissipation applications. Tubes can also be used as the pass devices. The snubber network (2R7 + 1uF mylar cap) on the output and the cap on the adjust pin are very important for proper transient response. Test your LM317s at low voltage to be sure they are stable before using them at high voltage. Maida PCB sold on eBay.