ASM-2?

[Sean Costello]

Hi all:

I've been bitten by the analog bug again, and have begun soldering in earnest
(as opposed to programming filters in C for Csound, which has been what I have
been working on for the past year or so). I have an ASM-1 PC board, and am also
working on various other circuits. I am starting to realize just how nice having
a PCB to work from is. The diode ladder filter is taking shape, but I am getting
sick of running all that bus wire around on the vectorboard...

I have a bit of a dream - a strange little nerd dream, but one that many people
on this list could probably relate to. :) It would be nice to have an "ASM-2"
PCB - a PCB that contains circuts that were not included on the original ASM-1,
that would be found in some of the nicer modular systems of the past. In
addition, it would be great if the ASM-2 board could be used by itself, as an
audio processing system, or maybe as a simple stand-alone synth.

Some of the modules that I think would be useful in the ASM-2:

- Ring Modulator. Could be AD633 design, or a switchable VCA/RM as Ian Fritz
described in Electronotes (based on an LM13600).

- An additional VCO, similar to the ASM-1/Electronotes VCO, but with additional
triangle and sine outputs. Used with Ring modulator, or as an additional VCO for
an ASM-1 based system.

- Sample & Hold. 

- I guess an added noise generator would be useful to use the sample & hold in a
stand alone unit. This part of the PCB could be left blank if an ASM-1 is part
of the system.

- Preamp, for external signals. 

- Envelope follower (preferably with selectable attack and release times). The
LM3900-based design in the Electronotes PCC looks useful, as it has different
attack/release times, and can be used as an AR envelope generator if a gate is
applied. I'm sure that a standard quad op amp could be used in place of the
LM3900, as the various components of the circuit (preamp, full-wave rectifier,
buffer for AD capacitor, differentiator) could be constructed using standard op
amps.

- A voltage controlled slope generator-type thing, similar to the Serge module,
or the "trapezoid" generator on the VCS3. This would generate AD/AR envelopes,
as well as act as an LFO, where the AR envelope would cycle. Voltage control on
the attack and decay times would be included; voltage control of the "off" time,
as in the VCS3, would be very nice as well. 1 volt per octave control over
attack and decay times would be useful for using this circuit as an additional
oscillator. Anyone have any useful schematics? The Serge DSG seems really
cool...

- A 4-pole lowpass filter. The Moog ladder is an obvious choice (probably the
best choice), but a 4-OTA/buffer structure might also be nice, especially if it
was switchable between lowpass and allpass. A temperature-compensated expo
generator, with linear FM, would be quite tasty.

- Comparator.

- Pulse divider (for suboctaves and other applications).

- Various utility modules - mixer, inverter, etc.

- Any sort of waveshaping circuits would be nice.

- Frequency shifter (well, this might be better as a circuit board on its own).

I'm sure that there are plenty of other circuits that would be useful, but it is
a question of how many would fit on a circuit board. All of the modules should
follow the same standards as the ASM-1 modules, in terms of voltage range,
temperature compensation, general high quality, etc. 

So, anyone want to do this? ;) As I said, it is just kind of a dream of mine - I
wish I had the know-how to design something like this myself...

Sean Costello