Moog 904A lowpass filter Question

[Joachim Verghese]

Hi!

> 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?

I think Juergen posed the same question some time back, but we
couldn't come up with any good explanation for the inclusion of
those two diodes.

As you say, the signal levels in the ladder are much too low
to make the diodes conduct, even with a hard-driven signal input
(as in the Pro Soloist).

Perhaps the board layout is simpler with the extra transistor
wired like that (3086 pin 13 run via pins 1 and 2) -- can't think
of any other reason.

-joachim