CA 3080 Tri to Sine converter question

[List, Christopher]

BTW, I would invite anyone with one  of these waveshapers to add a VC
input by simply attaching a 100K (or maybe 47k) resistor to pin 5 of the
CA3080 - in parallel with the existing resistor. Connect the other end
of the resistor to a panel jack and you're done. I've actually only done
this experimentally and never actually permanently added the mod. to any
of my VCOs - but I remember that the effect was pretty cool considering
how easy it is and the only reason I didn't make it permanent was
because I was too lazy at the time to drill an extra hole in a finished
module.

- Chris

> -----Original Message-----
> From:	Scott Bernardi [SMTP:scott.bernardi at fritz.com]
> Sent:	Wednesday, May 20, 1998 12:00 PM
> To:	synth-diy at mailhost.bpa.nl
> Subject:	Re: CA 3080 Tri to Sine converter question
> 
> The CA 3080 sine converters are very sensitive to the level and DC
> offset
> of the triangle wave coming in. How the triangle is created really
> doesn't
> matter., as long as the incoming levels are approximately the same.
> They work by overdriving the differential pair input of the 3080 into
> nonlinearity, with the effect of "rounding off" the tops and bottoms
> of the
> triangle. The "waveform adjust" on a sine shaper will adjust the
> amplitude
> of the signal coming in. Thus a +/- 10v peak triangle coming in will
> round
> more than a +/- 5v peak traingle.
> The "symmetry adjust" is actually just balancing out any DC offset in
> the
> input waveform and/or offsets in the 3080 so that the nonlinear
> distortion
> is symmetrical. A DC offset waveform, such as a 0v to +10v sawtooth,
> would
> warp on the top end and be sharp on the bottom.
> You could put any waveform into the since converter and get a rounding
> effect, which will have the effect of removing higher harmonics,
> >kind< of
> like a tracking VCF, except it would also induce some nonlinear
> harmonics. 
> 
> 
> At 09:07 AM 5/20/98 -0400, you wrote:
> >Hi all
> >
> >I was thinking about those CA 3080 tri to sine converters in Barry
> Klein's
> >book recently, and it occurred to me that rather than build one into
> each
> >oscillator, it might be nicer to have a few undedicated converters
> sprinkled
> >throughout one's system as independent waveshaping modules. Has
> anyone tried
> >this? Will it put out a good sine wave from a variety of different
> triangle
> >sources (such as 3340, ARP, ASM-1 LFO), or does each converter need
> to be
> >"tuned" for each oscillator? It may also provide interesting timbres
> for non-
> >triangle waves. Maybe you could have (switchable) front panel
> controls for
> the
> >shape and symmetry.
> >
> >Just a thought.
> >John B
> >
> >
> --------------------------------------
> Scott Bernardi
> voice: 415-538-0439 (note new number)
> fax:   415-904-8375
> scott.bernardi at fritz.com