[sdiy] SAW core VCO flyback time

[Donald Tillman]

> On Sep 5, 2016, at 11:17 PM, Tim Ressel <timr at circuitabbey.com> wrote:
> 
> I was just going to comment on this. The reset time is a negative because it is unpredictable. If a fixed reset is generated on purpose then it is predictable and can potentially be calibrated out. The Chroma, using a 4151 IC (datasheet?) serves this function.

The Chroma VCO uses a charge pump to reset the cap in such a way that the reset time does not flatten the high frequencies.  It's a pretty elegant design and described very well in the service manual:

    http://www.rhodeschroma.com/?id=circuitdescriptions#dualchannelboard

Traditional sawtooth VCOs have a small but finite reset time that does flatten the high frequencies, and that should be compensated for, but it can't be compensated for exactly, and the calibration procedure can be difficult.

  -- Don
--
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com