Moog 904A lowpass filter Question

[Terry Michaels]

Hi Joachim:

The Moog ladder filter was discussed at length recently, but I was just
thinking about the following:  do you or anyone else know why the ARP 4034
and 4035 modules, which contain the classic Moog filter ladder, have two
diode connected transistors connected from one side of the ladder to the
other side, across the lowest and third from lowest capacitors?  What's
really interesting is both of these transistors (or diodes, to be accurate)
are connected facing the same direction.  If the goal was to produce
clipping, the clipping will be asymmetrical.  I'm not sure if that is why
the diodes were added, though.  The emitter to emitter voltage swing is
maybe 50 to 75 millivolts between the emitters of the ladder transistors,
but it will take 500 to 600 millivolts to turn on one of these diodes, so
the diodes don't seem like they would serve any purpose, as they will never
go into conduction.

Terry Michaels