[sdiy] XR2206 VCO -- worth it ?

[Tim Parkhurst]

On Fri, Feb 18, 2011 at 7:54 AM, Andre Majorel <aym-htnys at teaser.fr> wrote:
> I'm pondering whether to get a bunch of XR2206 before they go
> away. Thomas Henry managed to get 1 cent linearity from 60 Hz to
> 7.7 kHz :
>
>  http://birthofasynth.com/Thomas_Henry/Pages/XR-VCO.html
>
> A single-chip VCO would be nice for a poly synth. But the part
> count isn't that different from the usual saw core design. You
> still need a polystyrene cap, a matched pair and a tempco
> resistor.
>
> Feature-wise, you gain an unusual triangle-sawtooth hybrid but
> you lose PWM and the separate outputs.
>
> On balance, I get the feel that it's just not worth it. Am I
> missing something ?
>
> --
> André Majorel http://www.teaser.fr/~amajorel/
> _______________________________________________

Hi Andre,

I sell a PCB based on Thomas' XR VCO. I've added a couple of
suboctaves and PWM (six separate waveforms in total). You still need
to switch between sine or triangle outputs, but the waveform skew
feature is very cool. Yes you still need a tempco and a matched pair,
but they're both NPN so that makes the job a bit easier (buy a bunch
of NPNs and select the closest two), and I usually have the 2K tempcos
in stock (out right now, but more are on order). To sum it up, I
really like the sound of this VCO and it's a very different character.
I think everybody should have one, but I don't know if I'd use it for
a new poly synth design.


Tim (all skewed up) Servo
-- 
"Sire, the church of God is an anvil that has worn out many hammers."
- H.L. Hastings