[sdiy] 566 Functional Replacement

[Quincas Moreira]

but the dream VCO chip would also do Through Zero FM!!!! <3




On Mon, Mar 19, 2018 at 11:55 AM, Tom Wiltshire <tom at electricdruid.net>
wrote:

> This *is* definitely a 8-bit PIC design. Here’s a sketch:
>
> Run an NCO as fast as you can. Output a triangle wave. You minimise the
> problems caused by aliasing, since the harmonics roll off so fast, plus you
> can whack the sample rate way up since all you need to do to generate the
> waveform is invert the phase accumulator for the second half of the wave.
> Wave output goes through a simple RC filter off chip, then back through an
> on-chip comparator for your square output with no aliasing either. Bonus
> points if you can open up the other comparator input to allow PWM.
>
> Tom
>
> ==================
>        Electric Druid
> Synth & Stompbox DIY
> ==================
>
> > On 19 Mar 2018, at 16:26, Tim Ressel <timr at circuitabbey.com> wrote:
> >
> > When I sed 'VCO' I did not mean a full-featured volt per octave VCO. I
> literally meant an oscillator that has voltage control. Cv in, triangle and
> square out, thats it. thats what the 566 did. that is what I want. 8 pins,
> 5 passives, and you're in business. thats what the 566 brought to the party.
> >
> > -t-i-m-b-o-
> >
> > On 3/19/2018 9:21 AM, Mattias Rickardsson wrote:
> >> Some thoughts about the dream VCO discussions here:
> >>
> >> What would be the main reasons for wanting a tiny VCO IC?
> >> I can find it hypothetically attractive, sure, but given that it will
> never have many features AND a small size at the same time, I'd almost
> always need to add stuff outside in the end since you rarely want just the
> basic functionality. If I'd use a dedicated VCO IC I'd rather have some
> features that are sometimes not in use than having to add near-basic
> functionality with external components. The only true reason for a small
> chip that I can come to think of is cost. I guess it somehow scales with
> size in IC fabrication?
> >>
> >> Making wishlists with VCO features, ending up on the 3340 specification
> from 38 years back... aren't we missing something? :-)=
> >> Many modern analog oscillators (both in modulars and in hardwired
> synths) have other features than the ones we had in the '80s. This should
> be reflected a bit in the wishlists we make for VCOs today, even if most of
> these features could be added outside the main chip. Exponential and linear
> CV should be mandatory, triangle/sawtooth/square outputs as well - and I'm
> thinking that a triangle core would be the way to go, even if proper sync
> needs to be dealt with in a less obvious way. That said, we're still stuck
> in 1980. Sine shaper, thru-zero FM, what more is desired for the
> synthesists of today? :-)
> >>
> >> Btw, Tim P, that negative expo CV allowing a single inverting CV summer
> is a smart choice. What about the double cap pins in your suggested pinout?
> Do they give a better solution than the cap-to-ground used in both CEM and
> SSM ICs?
> >>
> >> /mr
> >>
> >>
> >>
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> >
> > --
> > --Tim Ressel
> > Circuit Abbey
> >
> > timr at circuitabbey.com
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-- 
Quincas Moreira
Test Pilot at VBrazil Modular
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