[sdiy] New to the list

[Scott Gravenhorst]

Scott Bernardi <sbernardi at attbi.com> wrote:
>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".

The LM13600 data sheet PDF, page 11 fig 10 (National) has a floating
VCR.  Uses both OTAs.  It has some signal amplitude restrictions.

There's also a single ended version, but it's AC coupled.

>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
>>
>> --
>> Jihad Terrorism Conspiracy New World Order
>> Revolution Black Helicopters Freedom of
>> Speech First Amendment Rights: Carnivore Bait
>> go ahead and READ my e-mail I have nothing to
>> hide... how about YOU ???
>
>--
>Scott Bernardi
>sbernardi at attbi.com
>
>
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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