[sdiy] Re: Taking pre-orders for JH. 36dB/oct LPF now

Andre Majorel aym-htnys at teaser.fr
Thu May 28 01:23:23 CEST 2009

On 2009-05-18 19:19 +0200, JH. wrote:

> It's the *same* PCB, and the *same* order form.
> I just sent two emails because some people who are into phaser
> shopping may overlook it when they read filter, and vice versa.

Thank you. I hope the pre-order phase is not closed because I'm
still busy trying to wrap my head around that project. Here's
what I've got so far :

- varislope_filter_phaser_sch1.pdf is the "meat" of the project,
  the phaser/filter itself,

- varislope_filter_phaser_sch2.pdf is the PSU and the (very
  elaborate) modulation source that consists of Q11 + U18 = noise
  generator, U17B + C31 = S&H, U13 + C19 = LFO, U15 + U16 + U17A =
  wave shapers + scanner (I think).

The difference between the filter-only version and the full
version is that the modulation source is omitted and the 6 DG419
switches are replaced by straps.

I guess a third way to build the varislope would be to omit the
modulation source but keep the DG419 so it can still be a phaser
or filter.

Personally, I'm not sure about this modulation source. I suspect
that, on my unit, the waveform pot would be permanently stuck in
pure sine position, making the scanner redundant. The other
sources I see myself using (velocity, EG and sawtooth LFO) all
have to come from other modules anyway.

In theory, each pole could individually be switched between
all-pass (phaser) and low-pass (filter) under voltage control. If
all poles are sonically interchangeable, a single CV could be
used with the number of LP poles being 6/5 of the CV. No idea how
to do that, nor how useful it would be.

André Majorel <URL:http://www.teaser.fr/~amajorel/>

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