[sdiy] Scanner Vibrato emulation, first results

[jhaible]

> Hmmm good question.  I thought the V3 sample might have been defective...

No, it's really the same setting as C3, except the resistor that lifts the
whole delay line in chorus mode is shorted in vibrato mode.

> it sounds like
> there is a nasty low frequeny hum in there...
>
> I suppose thats from the tiny little motor you use to do the mechanical
> scanning  :^P

I was wondering where it came from, and I found this explanation:
There is a phase shift from one delay line tab to the following, so
while crossfading between them, there will be some cancellation,
modulating the amplitude. This happens 16 times per rotation,
and with a rotation speed of 412rpm = 6.87Hz the AM component
would be 16 * 6.87Hz = 110Hz. That's close to what we all know
as 2nd harmonic of hum from mains voltage feedthru.

I wonder if something like this happens in the original, with mechanical
scanner, too.

> ps: its sounds pretty good to me  :^)

Harry, whatever close or not-so-close it is to the Hammond,
it *must* sound good to *you*, because after all it's an
analogue chorus without BBDs !

JH.