Universal audio buffer / preamplifier with FET transistors

I was looking for a good supplement for my input selector project (described in this thread) for a long time an here it is!

In the beginning I wanted to make modified Nelson Pass B1 buffer (which sounds quite good in my system) but then I decided to upgrade it a bit to make it more universal. I designed PCB which can be:

• standalone FET buffer
• op-amp preamplifier (for example LM4562)
• op-amp preamplifier with FET output stage
• op-amp preamplifier with FET output stage in the feedback loop

There is also dc-servo circuit so the output capacitors may be omitted. Follow the link to download schematic of one channel of this preamplifier.

Measurements made with my e-mu 0202 shows that the THD+N is less than 0.001% for entire band.
This is how it looks for 1kHz, +-17V supply voltage and 10k load.