MOTM

Larry wrote:
>
>I like Mike's idea of CV control of the blend instead of PWM.  Since blend
>is actually changing the shape, it could almost function like PWM since PWM
>does change the "shape" of the wave.  Plus this gives us something
>"different" from the 300 waves and adds some diversity.

How about an output that goes from saw to square to narrow pulse??  Let's
ignore for a moment whether or not this is controlled from a knob or a
voltage.  The first half of the knob (or from -5V to 0V) goes from saw to
square, the second half of the knob (or from 0V to 5V) contains no saw and
goes from square (50% pulse) to 0% pulse (or 100% pulse, not that it would
make much difference).

So if it were controlled by a voltage, with no input the output would be a
square just like Paul suggests below.  However, this would also give the
option of saw to square blending in addition to VC PWM.

I think one of the best points made in this discussion is that saw to
square blending can be achieved with two VCA's and a mixer (if by
"blending" one means simply summing the two signals, although Paul might
have some other sort of waveshaping in mind), and that MOTM already offers
a mixer and two VCA's.  However, afaik, there is no way to do PWM unless it
is built into the oscillator.

Imho, being able to modulate pulse width with a voltage is much more useful
than being able to set it with a knob.  Now, if it had both a knob and a CV
input, the knob could provide an offset voltage, and the module could
provide a fixed output other than square without using a voltage source.
Although I'd much rather have a 310 with five jacks and three knobs.

Paul S. wrote:
>
>To refresh: this is a lower cost VCO that shares MOTM-800 EG panel,
>bracket, and pcb size. That means 4 knobs and 4 jacks.

Good for you!!

>In order to match MOTM-300 performance, and to use common parts I want to
>keep it SAW-based (as opposed to TRI-based). Looking at the pcb space and
>>cost target ($169-179 kit) I propose the following:

I like triangle waves as much as the next guy, but regardless of cost, saw
is much more practical.

>4 knobs are:
>
>COARSE
>FINE
>FM (attenuator)
>WIDTH (of pulse)
>
>4 jacks are:
>
>1V/OCT
>FM
>SAW
>PULSE

Groovy :)  I didn't like the mock-up I saw earlier that only had TRI and
VAR (saw to square controlled by a knob) outputs.  This new configuration
is much better :)

>This minimizes parts count. Having a 'blend' pot (say between SQUARE and
>TRI) looks like too many parts to fit on the board. Plus it adds $10-$15
>to >the cost. Since this main function of the '310 is to 'beef up' the mix
>with
>existing '300s, and to use as a sync generator to other '300s, this looks
>like the best fit.
>
>The only other possibility is: the 4th pots is a 'blend'. The VCO
>has 1 OUT. The 4th jack is PWM IN. With no
>plug inserted, the PULSE is 50%. Else, the input is a -5V to +5V pulse
>>width control (no input attenuation).

That is very clever, but wouldn't you need a square or saw available at all
times to make it a good sync source to use with a mini-wave or 300??

Is there any way to add a fifth jack to output a fixed waveform for use as
a sync source??  What if you lose a knob and go with my dual-function CV
idea??  If the dedicated output were saw, and the variable output without
any CV input is square (as stated in all four proposed designs), wouldn't
that would be the most useful con carne configuration??

Also, jacks cost significantly less than pots.  So if the purpose of this
module is to provide a sync source and beef up the mix, three knobs and
five jacks would work better.  This would also satisfy its requirements as
a space-saving lower cost VCO.

>So you can get SAW to PULSE with the blend. This is not as gnarly as the
>>TRI stuff, and possibly more musically useful.

Yes, I agree that saw to pulse blending is more useful than tri to square
blending.  Otoh, tri to saw blending is nice for bass patches.  Then again
you can't have everything :)