Preamp Recommendation for First Watt F4

I was referring to the more recent Pass Korg B1, much better than the original Pass B1.

I would build the basic kit without mods before investing in an expensive tube line stage. Careful with used units since the Korg Nutube 6P1 is very microphonic which will cause problems if not mounted properly. This inexpensive kit will improve that considerably:

Anti-vibration Mount for Korg Nutube 6P1

I'm guessing mine with mods and external linear supply will hold up well to both my main tube lines stages, both above $10k, especially since I will be able to dial up any amount of second harmonic distortion by simply adjusting the bias pots.

Many folks are reporting excellent results with the Pass B1 with Korg triode.

I'm currently building one for my F5 amp and to try with other stereos. I'm adding film coupling caps and an external linear power supply but otherwise stock. If I really like it, I'll add remote control volume later.

The first link is for the kit ($299 complete). The second is a lengthy build thread.

It would be interesting to see how much better the line stages the OP lists are than this inexpensive kit when built with decent film coupling caps. The stock electrolytics are 10uf. Recommended film values to keep size down are 0.22uF for the first cap in the signal path, 1uF for the second and around 3.3uF for the output.

B1 with Korg Triode (B1K) Full Kit

B1 with Korg Triode Build Thread