Jeff,
I'm answering your questions inline below. Have you seen my CGS VCO
project? I built a minimal VCO with a modified schematic.
http://www.pugix.com/cgs-vco.htm
-Richard Brewster
Jeff Laity wrote:
the ASM-1 has an op amp mixer for PWM. To mix an initial PW with a
control voltage you would need to add an op amp for active mixing. In
practice, I find that mostly what I need is an attenuator pot for the
PWM level, and I leave initial pulse with at 50%. You can add a 100K
panel pot as an attenuator with the wiper connected to the PWM input.
That would work fine to attenuate the PWM CV. I have two MOTM-300 VCOs
and I find I don't use the initial PW pot nearly as much as the PWM
level pot.
resistor to the summing node of the FM op amp. You can add more FM
inputs at whatever sensitivity level you want. You won't damage the op
amp or the VCO. 100K gives you a 1V/OCT response. Lower values give
less than 1V/OCT, higher more than 1V/OCT.
switch on my one FM input jack, so I could route it either way.
whole circuit, even if you don't bring all of it to your panel. It's
only a few cents worth of parts.
http://launch.groups.yahoo.com/group/ModularSynthPanels/
I'm answering your questions inline below. Have you seen my CGS VCO
project? I built a minimal VCO with a modified schematic.
http://www.pugix.com/cgs-vco.htm
-Richard Brewster
Jeff Laity wrote:
> I'm looking at a pair of the CGS48 VCOs as my first project. I want toIf you compare the ASM-1 VCO schematic with the CGS VCO, you'll see that
> build it in Eurorack format (12V with an adapter power cable) using
> the 12V mods listed on the project page. I've done quite a bit of DIY,
> so I'm semi-confident I can handle this one. I have a few questions
> about the project:
>
> - I don't see an initial pulse width on the schematic. Could I just
> add a 100k lin pot with the wiper selecting between V+ and V- into a
> 120k and merge it with the PWM CV in, as the electronotes article
> shows? Or would I need to change resistor values?
>
the ASM-1 has an op amp mixer for PWM. To mix an initial PW with a
control voltage you would need to add an op amp for active mixing. In
practice, I find that mostly what I need is an attenuator pot for the
PWM level, and I leave initial pulse with at 50%. You can add a 100K
panel pot as an attenuator with the wiper connected to the PWM input.
That would work fine to attenuate the PWM CV. I have two MOTM-300 VCOs
and I find I don't use the initial PW pot nearly as much as the PWM
level pot.
> - If I'd like to add an additional FM in, can they just sum together,It's easy. See my schematic. I added a Fine Tune pot with a 4M7
> or would I need to change the resistors? Is there a danger of
> overloading the opamp if both are sending 12V?
>
resistor to the summing node of the FM op amp. You can add more FM
inputs at whatever sensitivity level you want. You won't damage the op
amp or the VCO. 100K gives you a 1V/OCT response. Lower values give
less than 1V/OCT, higher more than 1V/OCT.
> - To add an FM Amount control, is this just a 100k lin attenuator pot?Yes.
>
> - What's the difference between the Processor input and the FM input?The Linear FM goes into a different place in the circuit. I added a
> Linear vs. Log scale?
>
switch on my one FM input jack, so I could route it either way.
> - If I'm not going to implement the suboscillator, just don't stuffIf you're using any part of the waveshapers, I recommend stuffing the
> anything past staircase in on schematic? Or do I need to ground any
> additional pins on LM3900?
>
whole circuit, even if you don't bring all of it to your panel. It's
only a few cents worth of parts.
> - If anyone has front panel layout ideas for Eurorack I'm all ears.Check out the ModularSynthPanels Yahoo group.
>
http://launch.groups.yahoo.com/group/ModularSynthPanels/
> Thanks, -jl
>
>