Here is a nice mod developed by Duane Balvage which replaces the noise generator with a sub-oscillator. The input off of pin 4 (the integrator cap pin) of a 3394 CEM drives the circuit. It is run through a high-impedance comparator to create a square wave. The square wave is fed to a 4013 flip flop configured to toggle once every 2 clock cycles (thereby dividing the frequency of the square wave in half). The output is attenuated and capacatively coupled to pin 9 of the 3394 that has been bent up out of the socket (to disconnect it from the "noise" circuitry). [Note: You might want to consider stacking two IC sockets and bending one of their pins to avoid a costly mistake.] The input of pin 9 is limited to about 80mV p-p, so adjust trimmer 2 until no distortion is heard. This circuit has to be duplicated six times (for each voice of the Six-Trak/MAX). The parameter "osc/noise balance" now controls the "osc/sub-osc balance". The effect is similar to the sub-oscillator on a Juno 6/60/106. Duane has modded his Six-Trak and reports that, "it gives the Six-Trak more OOMPH in the low end, and makes it more versatile sounding" One final word from Duane, this mod is "not for the faint-of-heart, and the author assumes no responsibility".
