[sdiy] Yusynth VCO

[yves usson]

Hi cheater cheater

As I say on my web page I tried to design my own stuff (mostly to get a 
grasp on the heart of the thing) and each and every
time, after runing simulation under spice I ended up with circuits that 
corresponded to other existing designs. It's a bit like cars once the 
manufacturers have started useing computer siulation for aerodynamics 
their cars started to look very similar whatever the brand !

Therefore I ended up with a very classical design which for its core is 
very close to Tony Allgood's VCO.
The actually "original" claims I may have concern i) the use of the 
regulators (working on a  non-usual regime)
to isolate and stabilize the core of the VCO. And ii) the use of quite a 
small value (220p) for the timing capacitor.
The idea here was guided by the fact that the exponential characteristic 
of the expo trannies is very good
for very low values Ic but starts to degrade for higher current. This 
means that the V/Oct tracking is allways
better for low octaves than for higher.
Since this VCO is not designed to be used as a LFO, I chose to use a 
very small cap value to shift the
frequency range for which the Vbe/Ic relationship is perfectly 
exponential to higher values.
It is important to use a high grade cap (stiroflex or silver mica) with 
low temperature drift.


To answer Ian Fritz question, the tests I ran gave a excellent V/OCT 
tracking from 16Hz up to 6.5kHz
(roughly 8 octaves) and then started to slightly degrade.
For thermal stability, I measured a deviation of 5 cents over 2 hours 
with a room temperature change of  2.5°C.
At startup the VCO is stabilizes after 5 minutes, and usually when I 
switch off the VCOs at night and switch them
on the day after 5 minutes they are at the same tune as the day before.
This is for the LM394/OP2137 version, I have no figures for the other 
versions.

Yves, yusynth
---------------------------
yves.usson at yusynth.net



cheater cheater a écrit :
 > Cool.. any idea what other (more classic?) VCO design they are based
 > on or the closest to?
 >