[sdiy] Aries modular schematics detail

[Grant Richter]

Here are some educated guesses. Since the replacement circuits work like the
originals they are probably not too far off in design.

> "a series of carefully selected and temperature compensated
> components which have been potted together as part of the printed
> circuit board.   The effect of this potted block is to create
> exponential currents in R13 and R31 as a function of the voltage at
> the junction of R8, R10 and R11."

This is just Terry Michaels NPN-PNP exponential converter. That is to say, I
replaced a broken block in an Aries state variable filter with Terrys
circuit and it worked fine. If you look at it carefully you can see the
emitter resistor for the NPN follower and the current limiting resistors for
the collectors of the two PNPs. As far as I know the blocks just contained
matched transistors, but there may also be a tempco in there for the VCO
block.

> 
>> Also, the module 329 Flanger has a part called PD10 with no other marking.
> 

Think of a dual string of diodes (or diode connected transistors) with
capacitors in parallel with the diodes. The AC impedance of the diodes is
varied with a control current and forms an allpass network in parallel with
the capacitor. The circuit is nearly identical to the Tau Systems phaser. It
is very similar to the Moog transistor ladder filter in the way the signals
are input and output from the ladder element. But the change in capacitor
position makes it an allpass instead of a lowpass. The literature says it
produces 5 notches, which would correspond to 10 stages.