Tracking measurements on ASM-1 VCO

[jorgen.bergfors at idg.se]

Hi all.
Yesterday I made some mesurements on my ASM-1 VCO clone, to test my new CV quantizer.
The CV quantizer outputs CV for octaves and fifths. It is based on John Simonton's 4 bit quantizer and consists of two TL074, one 4066 and a bunch of resistors.
The following voltages was output by the quantizer:

0.000
0.498
0.996
1.494
1.997
2.495
2.996
3.494
4.002
4.500
5.001
5.499
6.002
6.500
7.001
7.499

I didn't use the fifths for the tracking tests. The following frequencies were obtained from the VCO:

voltage frequency
 ideal  measured
0 32.1 33
0.996 65.4 65
1.997 130.8 131
2.996 261.6 262
4.002 523.3 524
5.001 1047 1047
6.002 2093 2094
7.001 4186 4182

As you can see, the tracking is pretty darn close to perfect over an eight octave range. And this was not with (expensive) MAT-02 transistors for the expo converter. I used the super cheap BC847BS.
With the CV quantizer it is really quick to adjust the tracking, by the way. The fact that the ASM-1 VCO doesn't have a high range trimmer simplifies the trimming a lot too, of course. Trimming it to this accuracy took me only a couple of minutes.

/Jörgen