[sdiy] Grant's Tracking Generator Calibration

[Grant Richter]

Hello

On Nov 21, 2006, at 3:02 AM, <Gergo.Palatinszky at nokia.com> wrote:

>
> The source is here:
> http://www.musicsynthesizer.com/DIY/Grant/CVtwister.html
>
> That's clear that 50k trimmer for setting the right saw frequency of
> 555.

The 50K trimmer is there to adjust the dither frequency to 44.1  
kiloHertz (no super important, just a common number).

> 1 MOhm trimmer before the "interpolate" pot. Can effect to the  
> amount of
> the "interpolate"-effect

If you look at the scope photos at the top of the page. One shows a  
square wave train with each alternating stage set to zero or max and  
the "Interpolation" pot set to zero. Under that is a series of  
triangle waves with a note that the "Interpolation" pot is set to  
max. The 1 meg trimmer in front of the 100K is adjusted so the  
triangle tips just meet with the "Interpolation" pot set to max.

> The 5k trimmer to LM3914 can shift the voltage range where LEDs are
> operating.

I'm pretty sure the 5K trimmer is adjusted to get +10 volts at pin 6  
and 7. This sets the input range.

> And there are an other 1M trimmer before the final output buffer.

Set "interpolation" to minimum. Put the +/- 5 volt range switch in  
the +/-5 volt position. Set one output stage potentiometer to max,  
and select that stage, then adjust the 1 meg trim for 5 volts out. If  
my math from 2001 is correct, this should set an output range of  
around +/-5 volts for the sliders instead of 0 to 10 volts. The input  
is offset also.

Have fun! The circuit runs at audible rates and can be used as a  
waveshaper, control voltage bender, sequencer etc. For a sequencer,  
the interpolate control acts like portamento (kind of).