ARP 4034/4035 (was: Moog 904A lowpass filter Question)

[Joachim Verghese]

Hi Terry,

> The diode connected transistors are the ones connected to pins 1, 2
> and 3.  Pin 13 is the emitter of one of the 5 transistors in the
> CA3046/CA3086, and is the substrate connection, but that is not the
> transistor that is connected as a diode.

This is how I see it, following Dana's comment:

Each collector in the 3086 array has an internal diode connected to
the substrate. This prevents the collectors from going more negative
than the substrate (by a diode drop).

The diode-connected transistor does the same job for pin 3, which
is one of the "lower" emitters in the ladder circuit. But then of
course, there must be something seriously wrong with the circuit
for pin 3 to go significantly more negative than pin 13.

Indeed, some versions of the 4035 filter has pins 1, 2 and 3 shorted,
thus omitting the diode connection (like the Quadra phaser ladder).

-joachim