Strange modulation schemes
dave.halliday at greymatter.com
Thu Jun 26 06:02:38 CEST 1997
> All this talk about random CV generators (sometimes called
> animation CVs) makes me think of a somewhat demented scheme
> I thought of recently for my tube synth circuits.
> John Atwood has this General Radio pink-noise generator from
> the 1950s. It uses a 6D4 thyratron surrounded by a big alnico
> permanent magnet. Apparently the field biases the ionized
> gas, producing substantial noise. It is sensitive to the
> magnetic pole placement versus the thyratron internal structure.
> A bizarre scheme, but it apparently works well.
> So: why not glue a bunch of small rare-earth magnets to the rim
> of a wheel and spin them past a tube? Use a motor with a speed
> control. This would work with ANY kind of tube....12AX7 or pentode
> amplifiers, beam modulators, even the thyratron VCOS in my synths.
> The small magnets used in disk drives are cheap, readily available
> as surplus, and VERY strong. Glue them to the wheel in any
> desired pattern, and you'll have that pattern imposed on the
You could also use the "tuning eye" flourescent tubes and use a
photocell to pick off the values.
There is also a fun sort of feedback that can be done with a TV
monitor and camera - focus the camera on the monitor. YOu can get
nice random pulsating patterns - tilt the camera a bit and also pass
your hand between the two.
I once did a show that had film cans with CDS cells glued to the face
of a B&W monitor - used nice thick cable coming out the back. These
went to various CV inputs and the camera focused on the room.
--- Via Silver Xpress V4.4 [Reg]
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