[sdiy] SAW core VCO flyback time

Roman Sowa modular at go2.pl
Mon Sep 5 11:36:25 CEST 2016

It makes the waveform amplitude shrink with frequency, that's the main 
drawback I think, as it impacts waveshaping.

In Chroma VCO the reset charge phase is about 33us according to the 
schematics and VFC datasheet, so with increasing frequency the waveform 
is slowly morphing into a triangle of half nominal amplitude which 
happens at about 15kHz (66us cycle). At 4kHz the reset slope takes about 
13% of full cycle, so it only begins to look like a triangle, and the 
amplitude is 13% percent smaller than low frequency sawtooth.
OTOH Franco compensation also does that to some extent, a bit smaller 
but still.

Chroma VCO is basicaly a triangle core VCO with one slope fixed.


W dniu 2016-09-03 o 13:42, Mattias Rickardsson pisze:
> On 30 August 2016 at 23:41, Donald Tillman <don at till.com> wrote:
>> The ARP/Rhodes Chroma VCO had a unique charge pump VCO core that had a long reset time, but the reset didn't introduce a tuning delay in the cycle.
> That's interesting, a neat way of getting rid of the time issue - but
> why isn't this more widely used? Were there other drawbacks or
> imperfections that made it less practical?
> Speaking of the ARP/Rhodes Chroma,
> if anybody has the service manual in a better PDF form than
> one-PDF-per-page then I'd be more than happy to take a look. :-)
> Impressive info site, however:
> http://www.rhodeschroma.com/?id=servicemanual
> /mr
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