Preamp for Pass X350.

I have an X150 and have had excellent results with the Placette. And you should certainly consider the PAss pre-amp. Wth tubes, be mindful that the output impedence of the pre-amp should be 1/10th or less the input impedence of the X-350, which is probably around 22K (on the low side for amplifiers).

Match it up with any of the Nelson Pass preamps, even going back to his Threshold days. Pass X-0, Threshold Fet 10E are two of his best preamp designs. Also, a Threshold T-2 balance preamp is excellent synerygy even though it's not a Nelson Pass design.

I heard an X350 driven by a Pass pre and was VERY impressed. It now as me thinking about an upgrade. (please wife don't hit me ... I won't say THAT 'U' word again)