[sdiy] Moog SL-8

[Tom Wiltshire]

On 18 Apr 2017, at 07:17, Andre Majorel <aym-htnys at teaser.fr> wrote:

> On 2017-04-17 11:30 +0100, S Ridley wrote:
> 
>> I read about the SL-8 (at NAMM?) in E&MM magazine way back
>> then, and was inspired to try to design an analog "VHM"
>> waveshaper, but it ended using almost as many parts as a
>> second VCO, so not really worth the effort.
> 
> Bummer. There are still advantages, though. Unlike a second
> oscillator, the wave shaper doesn't need adjustment. It's like a
> second oscillator that tracks the first perfectly but at an
> offset.

Ok, so where can I find out how this VHM thing works? Since the SL-8 was never released, there's no schematics or service manual out there as far as I can see. Can anyone explain it to me?
I understand how you do the Sync sweep effects with a DCO, but I don't understand how they've done oscillator detuning.

> Also, if I understand correctly, the apparent beating frequency
> is independent of oscillator frequency. Unlike a pair of VCOs
> detuned upstream from the exponential converter which always
> beat too slowly in the low notes and too fast in the high notes.

A linear offset, rather than an exponential one then. The Moog Taurus Mk1 famously had a linear offset control between the oscillators. I can't think of any other synth that has used it, but there are probably one or two others.

Thanks,
Tom