[sdiy] VCO - sine output - why bother?

[Ian Fritz]

On 8/28/2016 12:41 AM, mskala at ansuz.sooke.bc.ca wrote:
> On Sat, 27 Aug 2016, Donald Tillman wrote:
>> The Aries VCO, designed by Dennis Colin (who was responsible for much of
>> the early ARP synths), did something very similar.  It had an
>> exponential converter with twin outputs, one for a triangle wave core,
>> and one for a separate sawtooth wave.  And the peak of the triangle wave
>> reset the sawtooth wave.
>
> Interesting.  If using a sine core (oscillating two-pole VCF) in
> particular, you need two outputs from the exponential converter for that
> anyway, even if in practice people often just drive a couple of resistors
> with a single current source and call that good enough.  Having two it
> then seems quite natural to have a third output for some other core.
>

The multiphase VCO at my website uses four source transistors.  There 
are some effects from the transistors being slightly mismatched, though. 
  Also, as I mention there, the Sin core can be made using a limit-cycle 
oscillator rather than a feedback filter. This makes the outputs more 
the same amplitude- and distortion-wise.  Patchell published a 
quadrature oscillator design using this method many moons ago.

Also, I use five source transistors in my cyclic chaos oscillator, which 
can operate as a decature Sin oscillator.

Ian


-- 
ijfritz.byethost4.com