[sdiy] New to the list

[Scott Bernardi]

A voltage controlled potentiometer, if acting as a voltage divider (i.e., drive
one end of the pot, the other end is grounded, and take the output off the wiper),
is just a VCA, where the "output" goes from 0 to to unity (times the "input")
depending on the control voltage.
What is more difficult is simulating resistors or potentiometers where all ends
are "floating".
A "mix" circuit (two separate signals driving the ends of a pot, output taken off
wiper) can be done with two OTAs and some of opamps. Same with a "pan" circuit
(signal drives the wiper of a pot, left and right outputs taken of the pot ends).

I remember seeing a circuit for a floating voltage controlled resistor made up of
two OTAs in Electronotes somewhere.
But these involve some pretty extensive circuit mods.


harry wrote:

> Voltage controlled potentiometers can be made with Vactrols
> (LED-photoconductor)... Its not a cheap solution, and cannot get
> very close to either wiper... OTOH it will go into the circuit
> without interaction.
>
> Most controls could be voltage controlled resistors... MUCH easier
> to do.
>
> Maybe you don't need ALL controls... just the really useful ones ???
>
> H^) harry
>
> Paul Maddox wrote:
>
> > Stefan,
> >
> > > I've been lurking the Synth DIY lists for about a week (And going through
> > > the archives as well, excellent stuff!)
> >
> > hello there...
> >
> > > My Synth background is a little funky, I'm an Electronics Engineer, and
> > the
> > > reason I studied EE was because I was in love with telecoms and analog
> > > synths.
> >
> > I like the word 'funky' it just doesnt get used enough :-)
> >
> > > I'm the proud owner of a Minimoog and Micromoog and have been working on a
> > > project to build a MIDI to CV converter and rackmounting my mini and
> > adding
> > > the ability of storing the knob values via MIDI, hence me subscribing to
> > > this list.
> >
> > :-P
> > OK, fine way to start, make us all jelous!
> >
> > > To keep it short (And fire my questions away) I've decided to go for the
> > > PAiA implementation of the MIDI to CV controller (Since I'm very familiar
> > > with the 8031 and 8051 uControllers), anybody has some words of wisdom?
> >
> > Ive heard good things and bad things about this midi to CV unit...
> > take a look at the one Tony Allgood sells (MidiDAC), its popular and works
> > reliably...
> >
> > > My second question is about my pot to MIDI implementation... I decided to
> > > use a second microcontroller for it and use a LINEAR LTC 1851 ADC for the
> > > knob A/D (I figured out I needed around 20 ksps per control pot, giving me
> > > around 50 inputs once you take the overheads into account, which is far
> > more
> > > than what I need :) and 2 8091 DAC chips for the preset to voltage
> > > conversion... again any words of wisdom or experiences you want to share?
> >
> > Ok, you're going to have problems with the DACs...
> > Look at the schematics, some of the pots arent voltage sources, they are
> > resistances (resonance pot is the first one to spring to mind), so you'd
> > need to convert the filter to be FULLY voltage controlled...
> > Also take a close look at the EGs , I bet they've used resistance rather
> > than voltages for some of the parameters.
> > What you're planning to do is a MASSIVE task...
> > Im sure people here will be able to help though..
> >
> > > I intend to test this on a fatman kit before trying it with my Moog boards
> > > (Which I have already "cloned")
> >
> > Nice idea, again, compare the filter and EG circuits...
> > you big problem is going to be creating a voltage controlled poteniometer...
> >
> > Paul Maddox
> > _______________________________________
> > Wavesynth home page;-
> >     Http://www.wavesynth.com
> > Modulus synthesizers home page;-
> >     Http://www.modulus.wavesynth.com
> > PPG Synthesizer pages;-
> >     Http://www.PPG.wavesynth.com
> > Waveterm C Project page;-
> >     Http://www.waveterm.com
>
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--
Scott Bernardi
sbernardi at attbi.com