biasing the SuSy boards:
-before first power up, the pots that flank the THAT340 should be at their mid point. the outer biasing pots should be as follows, when looking at the board with the heat sinks at the rear: L - fully CCW and R - fully CW. leave the DC servo opamp out.
-bring up the bias by turning the L outer biasing pot CW and the R CCW, keeping tabs on the DC offset. both pots will increase the quiescent current bias, but also affect the amount of DC offset. i just turn them in equal amounts until i hit my target quiescent current and then tweak for lowest DC offset. the offset will fluctuate quite a bit, like 100mV. small fractions of turns on the pots will cause the off set to jump. be patient. i think the best i could do was roughly +70mV to -30mV.
-insert the DC servo. measure the offset between the O(+) and O(-) - i measured 20 and 25mV. turn one of the THAT340 pots CW and the other CCW, 1/2 turn each. note if the DC offset went up or down. if it went down, then continue turning the pots in the same manner, in 1/2 turn increments, until you reach 0mV. if the offset went up, then reverse the turns in the opposite directions.
-i was able to get less than 0.5mV offset and very stable. on cold start up, still a very low 2mV. zero pops or hiccups through my HPs either on power up or power down.