Variable ramp generator / Gnome

[Harry Bissell]

Gnome Warning: The controller was a "ribbon" so pitch accuracy was not an issue.
Most of us couldn't use it. The saw/inverted saw from Don Till sounds great. I can
live with amplitude error, but not pitch error. IMHO I don't really see the use for
this except as an LFO. Please somebody enlighten me...why.  :^( Harry (not getting
it) Bissell

Tim Ressel wrote:

> mb,
> Many eons ago Paia made a toy synth called a Gnome. The VCO they used had a
> "Skew" control that changed the output from a triangle to almost a saw. I have a
> zipped .pdf file, but its 1.5 megs. let me know if you want it and I'll send it
> your way.
>
> Tim Ressel -- Hardware DQ
> Hewlett-Packard
> Verifone Division
> 916-630-2541
> tim_r1 at verifone.com
>
> > ----------
> > From:         mbartkow at ET.PUT.Poznan.PL[SMTP:mbartkow at ET.PUT.Poznan.PL]
> > Sent:         Tuesday, July 06, 1999 8:51 AM
> > To:   synth-diy at mailhost.bpa.nl
> > Subject:      Variable ramp generator
> >
> > Dear all,
> >
> > Taking the wavetable discussion aside, I have another problem
> > and would love to hear your hints or comments.
> > In fact, this is my idee-fixe for years:
> >
> > I definitelly want to abandon the "mix several basic
> > waveforms" VCO approach. I just don't like it, because
> > it trades too much pots for unnecessary stages of freedom.
> > OTOH it is boring and yet another replication of an old and
> > worn-out scheme. My idea for an original VCO is to generate
> > a flexible waveform and shape it with some variable nonlinear
> > circuits.
> > First of all I need a variable ramp waveform, i.e. a waveform,
> > whereby the ratio of the rising edge to the falling one is
> > freely adjustable without affecting the frequency.
> > I know, it is possible to independently control the charge and
> > discharge times in integrator by using a pair of diodes or
> > a CMOS switch. AFAIR, Juergen described such operation of KORG
> > LFOs. The problem is if one applies this control scheme to VCO
> > it leads to severe tracking problems.
> >
> > My idea was to generate a stable saw or triangle and shape it
> > using a switched gain circuit. I must say I tried to design such
> > a circuit, but either I am too narrow minded or blind - I just
> > cannot come up with anything. I hope somebody invented this before
> > and would not mind to share.
> >
> > mb
> >
> >
> > --
> >
> > Maciej Bartkowiak, PhD
> > ========================================================================
> > Institute of Electronics and Telecommunication     fax: (+48 61) 8782572
> > Poznan University of Technology          phone: (+48 61) 8791016 int.171
> > Piotrowo 3A                             email: mbartkow at et.put.poznan.pl
> > 60-965 Poznan POLAND               http://www.et.put.poznan.pl/~mbartkow
> > ========================================================================
> >
> >
> >