Re: [AH] Modular VCO spec questions/comments

From Tim Parkhurst
Sent Wed, Sep 10th 2008, 07:38

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On Tue, Sep 9, 2008 at 9:00 PM, Paul Schreiber <> wrote:

> I am designing 2 new Frac VCO modules (1 analog, 1 digital) and I started
> looking at other folk's specs. Noticed that no one publishes (that I can
> find) what the scaling of the Linear FM input is. 500Hz/volt? 1000Hz/volt?
> Anyone have any ideas what would be a good spec?
> Second question: what would be an upper limit of +15V (-15V is pretty
> small) DC current spec? Is 100ma "a whole lot" or no big deal? The digital
> VCO uses 3.3V internally for the DSP (I have a little switcher for it). I am
> also looking at "high end" TI/Burr-Brown op amps that are supposed to be
> great sonically but suck current like no tomorrow. I'm going to have several
> people listen to different op amps to see if in this VCO instance, there is
> enough audible difference to justify adding 20ma current drain to the +15V
> line.
> For example, the Blacet Hex Zone is a 150ma module, and their 2100 VCO page
> lists nothing, "spec-wise" for power or the linear FM scaling. Maybe someone
> can measure it?
> Paul S.
Hey Paul,

I have no idea what the Hz/V law is on other VCOs, but how about a proposal:
On an expo VCO, we want to cover the audio range. This works out very nicely
because if we start at 20Hz and move up at 1V/octave, we can cover the audio
range with a 0 to 10V CV (we actually get to 20,480Hz at 10V). Since the 10V
CV range is already a well established standard, why not set the Hz/V
relationship so that a 0 to 10V linear CV also covers the audio range?
Basically, if we set the law to 2000Hz/V we can go from 20Hz to 20,020Hz.
Does this look reasonable, or did I stop making sense right after "Hey

As far as the power consumption, I'm not sure. I think 100mA is a
little high but it's worth it if the module provides some unique
functionality. Given your history of innovative modules, I'm sure you'll
have no problem with that ;-)

Tim (In the words of Dean Venture: "I DARE you to make less sense!") Servo
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