Psw, you seem to be right about the switching fault. Thanks for spotting it.
Meanwhile, I've finished my second driver. This time it's a short coil with steel core, 0,2 mm wire and 6 rare earth magnets. First thing I noticed was that the magnetic pull was much less than with my previous driver using ceramic magnet.
I tested it today with Fetzer / Ruby amp. Performance was much better than with my first version. This time I got infinite sustain easily with every string except high e. I also managed to get high e sustaining, but it's not that easy and consistent as the others.
I had both N1 and N3 versions of LM386 around, so I tested both. I was little bit happier with N3, but the difference was not very big.
My biggest concern is that the sustainer seems to distort my signal, which is going to amplifier. I suspect that this is caused by interference, I only connected the parts together with some test leads outside the guitar.
Another problem is that I couldn't get harmonic mode working properly. All I could get was high frequency oscillation. I was able to change the frequency with my volume pot, so I did get some interesting sounds, unfortunately that was not what I was after.
I had exactly the opposite results. Performance was much better without tone capacitor (I've left tone control out from this guitar, so I tested this with separate 22nF capacitor). I guess this depends on pickups, I have a dark sounding humbucker in bridge position and psw seems to be using single coil PU.
Next I guess that I'll put everything inside the guitar and see if a proper installation helps with distortion problem. I might also add a Zobel Network to my amp to see if that helps with oscillation in harmonic mode. I also have material for some more drivers, so I might try one using magnet itself as a core.
Regards
Pekko