Bastl Quattro Figaro linearization hack

The DIY Bastl Quattro Figaro I built had a quite heavy distortion:

so I connected the four unused diode bias inputs of the two LM13700 OTAs to +12V through four 68k resistors and replaced the 100k R6, R12, R19, and R25 with 33k to compensate for the gain reduced by using the linearization diodes

The distortion is now much better: