[sdiy] CMOS for linear circuits.

[ryan williams]

Hi Scott,

It is a CMOSed version of René Schmitz late MS20 filter. The VCF still 
uses OTAs so it's not completely CMOS. I kind of just decided no Opamps 
allowed. The OTA is a LM13700 and I did not use the Darlington pairs 
either. The filter I posted a few days ago. It's schematic and some 
example sounds are here on my web page:
http://www.sdiy.org/destrukto

With this configuration, it sounds great. the first inverter has 2.2M to 
  make it's input impedance high. I chose that value because it was 
within reach when I built it. I tried the same configuration on the 
second inverter so that I could have an HP input and it worked, but sort 
of ruined the sound I liked so much when using the LP mode. I also tried 
a few configurations of the feedback circuit, but I liked this one the 
most. If I end up with one of these in my modular, I will probably use 
another inverter to sum more inputs.

now that you have got me thinking about it not being all CMOS. I might 
try and replace those OTAs, but probably I will just leave it. This 
version has a super simple volt-current converter, just a resistor. So 
it is basically linear, but that is what I wanted on the theremin 
(atleast I think I do).

about your waveshaper. I considered this, and some waveshapers from 
Osamu's site. But, since the filter can create a good sine, I decided 
against having a shaped triangle or sine.

-ryan

Scott Gravenhorst wrote:
> I will be quite interested in your CMOS VCF.  I already use a CMOS VCO, 
> (René Schmitz).  There are several designs for CMOS VCFs on the web, what
> exactly do you plan?
> 
> I also made a CMOS sine waveshaper.  (and I've already posted that I have
> no idea how accurate it might be or not be, but it does work and it's
> output looks like a sinewave on a scope, it also sounds like a sine to my
> ears).
> 
> A very good site for CMOS stuff is:
> 
> http://www5b.biglobe.ne.jp/~houshu/synth/
> 
> This is Osamu Hoshuyama's site.