[sdiy] VCCO demos/schematic

[Ian Fritz]

Hi Rene --

Glad you liked the demos.  Really, they only scratch the surface -- for 
example, there is no modulation of the pattern or frequency.

The scope photos were taken at audio frequencies -- otherwise there is not 
enough trace persistence to see the whole pattern by eye.  Also, my scope 
is ac coupled in xy-mode.  As I mentioned before, I checked the V/Oct 
scaling over about 6 octaves, from around 1kHz down.  This is using 2700 nF 
caps.  Of course, a final unit would incorporate the usual expo control, as 
you suggest.

Unfortunately, it is quite difficult to display the orbits at very slow 
rates.  And you can't just turn the freq control down, as the pattern can 
change due to circuit nonidealities, e.g., the familiar bias dependent CV 
feedthrough.  A super accurate OTA would be very helpful here.  Any 
ideas?  Discrete?

   Ian


At 05:15 PM 10/28/2004, René Schmitz wrote:

>Would it be feasible to run it into audio ranges as well, and have it 
>"scale" by replacing the OTA resistors by exponential current sources?