Odp: [sdiy] LFO with variable waveshaping

[Roman Sowa]

Take a look at MS20 LFO. I made something similar with
SSM2164
as OTA, so it was VCLFO then. So I added 2 other VCAs from
the SSM to replace the pot in MS20 circuit. CVs of those 2
VCAs
were driven in oposite directions, i.e. one directly, second
via inverter.
Outputs tied together going to LFO core, inputs separated by
reverse
diodes going to SQR output. Usable range was when CVs
changed
from 0.22 to 2V (at SSM control pins).
It worked OK, frequency error measured while waveform
changed
from TRI to SAW was about 30 cents. Of course no real, sharp
edge
SAW, I had to stop somewhere. And it had terrible
temperature
dependency. That's why it never left the breadboard.

I had another idea once, derived from some theoretical
reasoning.
With AD633 one can make reciphrocal circuit, that can
replace
the pot in MS20 LFO. It should work much better than SSM2164
having log response instead of needed 1/x.
Never tried it tho so I don't know how AD633 errors affect
the frequency.

Roman

----- Original Message -----
From: Luis Marka <lmarka at yahoo.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, November 27, 2002 12:28 AM
Subject: [sdiy] LFO with variable waveshaping


> Hi DIY,
> I am thinking about building a LFO with waveshaping. It
would be
> something like this:
>
> Waveshape CV @ 0V:
> |\        |\        |\
> |  \      |  \      |  \
> |    \    |    \    |
> |      \  |      \  |
> |        \|        \|
>
> Waveshape CV @ 5V:
>     /\        /\
>    /  \      /  \
>   /    \    /    \
>  /      \  /      \  /
> /        \/        \/
>
> ...and @10V:
>         /|        /|
>       /  |      /  |
>     /    |    /    |
>   /      |  /      |  /
> /        |/        |/
>
>
> (Please use a non-proportional font in order to appreciate
the beauty
> of this fine piece of ASCII art).
> Any ideas on how to implement such an LFO?? I don't recall
seeing
> anything like this before...
>
> All my best,
> Luis Marka
>
>
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