Modular Synth Panels

Hi synth panelers,
I've been working through my 'backlog' of cgs modules. My recent
completion (with a lot of great assistance from Ken Stone) is the cgs vco.
I've uploaded a Schaeffer semi-motm 3U style panel to the
ModularSynthPanels yahoo groups site under Files, Cat Girl Synth Designs,
Schaeffer file: cgs.vco3U.4row.fpd.

Basically the panel contains every function from the pcb except a second
cv in, and it contains attenuators for FM AC, FM DC, PWM, SUB CV IN and
SHAPE CV IN. Note that the pot holes are smaller than those for Spectrol
or Bournes pots (I decided to use up some of my Alpha pots). The design
also has a FINE Tune pot location.

In a 3U standard motm design I would have lost an output or input
(excepting the 2nd cv in), so I decided to use my 4 row style (that is,
standard motm style has a total of 8 rows of sockets vertically, but as
Tony Allgood has shown us with the 410 filter companion, one can easily
fit in 9 rows and still retain good spacing for inserting jacks), since
the standard motm socket spacing would have required 4U (which I was not
willing to do). Adding in the 4th row increased the number of sockets
beyond what I needed, hence the additional 1v/oct input (3 1v/oct inputs
should prove interesting) was added.

IMHO This is a nice companion vco to the motm and Blacet vcos that I
already have (for example, I was after somewhat different waveforms).
However, I haven't nailed down the subosc section yet.

Constructive comments appreciated, Jeff

Very nice panel. Not sure how often I would use both the AC and DC
linear inputs at once. I might swap the DC linear FM input for a second
reversible CV input if I had to choose, or find a way to add an AC/DC
switch. But your large panel affords just about everything.

For a completely different and minimal approach, see the panel I've just
uploaded to the same directory: dual-cgs-vco.fpd. It is the VCO core
that interests me. I put two CGS VCOs into a 2U panel (1 in 1U would be
just half). I omit the Serge-lke CV inputs and the waveshapers. The
result is a VCO with features much like a MOTM-310, but with the
addition of SYNC and linear FM, and with separate SAW and PULSE
outputs. I use switches to select whether the FM input is applied to
one of the exponential control inputs or to the AC or DC linear input,
MOTM-300 style.

My first try at this panel substituted a CV input for the FINE tuning.
You can see it in the Richard Brewster Designs folder: cgs-vco-2.fpd, a
1U version. It is a little awkward because with the additional CV input
I had to use a switch to choose between SYNC and PWM input and also
could only have AC linear FM. The advantage it had was three total FM
inputs, one of them being the cool reversible CV. But after considering
how much I use my FINE tune pots, I decided in favor of those, and as a
bonus got separate jacks for SYNC and PWM inputs and could use the
second switch for AC/DC linear FM. Bye-bye cool reversible CV. (Hey,
but I have the Oakley Multimix!) With a full featured panel you don't
have this sort of dilemma. Everything in design involves some sort of a
tradeoff. That is partly what makes it interesting. The CGC circuits
offer a lot of possibilities for different panel designs. And Schaeffer
let's us do our own thing. 1U, 2U, or 3U, it's a choice we can make.

I haven't built my CGS VCOs yet, but I think they will turn out nicely.
I am going to use high quality parts throughout.

-Richard Brewster

Jeffrey Pontius wrote:

>Hi synth panelers,
>I've been working through my 'backlog' of cgs modules. My recent
>completion (with a lot of great assistance from Ken Stone) is the cgs vco.
>I've uploaded a Schaeffer semi-motm 3U style panel to the
>ModularSynthPanels yahoo groups site under Files, Cat Girl Synth Designs,
>Schaeffer file: cgs.vco3U.4row.fpd.
>
>Basically the panel contains every function from the pcb except a second
>cv in, and it contains attenuators for FM AC, FM DC, PWM, SUB CV IN and
>SHAPE CV IN. Note that the pot holes are smaller than those for Spectrol
>or Bournes pots (I decided to use up some of my Alpha pots). The design
>also has a FINE Tune pot location.
>
>In a 3U standard motm design I would have lost an output or input
>(excepting the 2nd cv in), so I decided to use my 4 row style (that is,
>standard motm style has a total of 8 rows of sockets vertically, but as
>Tony Allgood has shown us with the 410 filter companion, one can easily
>fit in 9 rows and still retain good spacing for inserting jacks), since
>the standard motm socket spacing would have required 4U (which I was not
>willing to do). Adding in the 4th row increased the number of sockets
>beyond what I needed, hence the additional 1v/oct input (3 1v/oct inputs
>should prove interesting) was added.
>
>IMHO This is a nice companion vco to the motm and Blacet vcos that I
>already have (for example, I was after somewhat different waveforms).
>However, I haven't nailed down the subosc section yet.
>
>Constructive comments appreciated, Jeff
>
>
>
>

> Very nice panel. Not sure how often I would use both the AC and DC
> linear inputs at once.

I have used the motm lin/dc and FM2 periodically, so I thought I would
continue some experimentation with the cgs vco. Maybe the reversible cv2
would have been more useful.

>But your large panel affords just about everything.
>

THis is mainly what I was after - bringing out as many features as I could
within the 3U confines.

> For a completely different and minimal approach, see the panel I've just
> uploaded to the same directory: dual-cgs-vco.fpd.

Very nice! The exp/lin ac/dc switching is a good idea (I'm assuming they
are set up like the motm 300?). You always have nice designs. Because
yours is a dual vco unit, there is certainly the opportunity to provide
some normalizing socket connections for ease of operation (e.g.,
normalizing sync sockets or FM sockets).

> It is the VCO core
> that interests me. I put two CGS VCOs into a 2U panel (1 in 1U would be
> just half).

I suppose from a different perspective, I am interested in the full-blown
version, in particular, the vco/waveshaping section. I had considered
eliminating the sub osc section, but thought it might be interesting to
experiment with.

> But after considering
> how much I use my FINE tune pots, I decided in favor of those, and as a
> bonus got separate jacks for SYNC and PWM inputs and could use the
> second switch for AC/DC linear FM.

Here I agree also - the Fine Tune pot is a must for me. I have one simple
vco that I built from a schematic and I did not include a Fine Tune (I
should have). After that, I decided to always have Fine Tune.

> Bye-bye cool reversible CV. (Hey,
> but I have the Oakley Multimix!)

How true! These are among the best 'utility' modules to have.

> With a full featured panel you don't
> have this sort of dilemma. Everything in design involves some sort of a
> tradeoff. That is partly what makes it interesting. The CGC circuits
> offer a lot of possibilities for different panel designs. And Schaeffer
> let's us do our own thing. 1U, 2U, or 3U, it's a choice we can make.
>

Yes, Ken's pcbs offer minimal or maximal modules, depending on one's needs
and space.

Trade-offs seem to be the rule, especially with limited module 'real
estate', which I always seem to be running up against. I had worked on 4
previous designs of 2U and 3U before I decided on this one. My thinking
just evolved into the 3U. That is one thing I like about having a program
like Front Panel Designer (or others): I can 'sketch' out ideas and think
about what aspects of the module that I would like at the same time - the
feedback is nice in exploring options.

> I haven't built my CGS VCOs yet, but I think they will turn out nicely.
> I am going to use high quality parts throughout.
>

I haven't spent a lot of time with this vco to date - just an overall
check out of sound and features. I have yet to figure out the STAIR
output - I don't have it nailed down yet.

Jeff