Piet,
I think the op-amps may be 'not guilty'. I swapped IC1 and IC2 with two from another kit (also the P types) and the noise is still present. I also used Dick's idea to trace the source by using my amp (actually my interface/headphones nd the first point I detect any hiss is at the drain of the FETs (both are similar). The hiss level at the pre amp outputs is louder (obviously as they amplify the incoming noise) so it looks like the Fetzervalve circuit is behaving like a real valve, it's hissing nicely
Without the ability to measure it, I can't tell if my signal/noise ratio is worse than -70dB. Interesting anecdote about the noise you were going to synthesise
I am going to leave the circuit as it is now until we test it through the AC30 at our Shadows Club meeting next Sunday. We'll see what the veterans think - I'm just a relative noob as far as authentic sounding vintage units are concerned
Incidentally, Piet, I love the tone the eTap2hw input circuit gives my guitar (Fender 59/62 pickups) so I may just end up enjoying the 'authentic' hiss as well