[sdiy] expo accuracy? or integrator accuracy?, or both?

[Magnus Danielson]

From: Scott Gravenhorst <music.maker at gte.net>
Subject: RE: [sdiy] expo accuracy? or integrator accuracy?, or both?
Date: Sun, 09 Feb 2003 06:20:15 -0800 (null)

> =?iso-8859-1?Q?Ren=E9?= Schmitz <uzs159 at uni-bonn.de> wrote:
> >Hi Ian, Hi Martin!
> >
> >>Of course, in the end you have to look at the whole picture and also work 
> >>especially hard at the "weakest links".
> >
> >Sure you have to identify the areas where you can the largest improvements.
> >But for that, you will have to do it for _all_ of them. That was the whole
> >point.
> >
> >>But you have to understand all the problem areas and what the limits are in 
> >>each area before you can do that.
> >
> >Exactly. Perhaps a good thing to see what the effects of open-loop gain,
> >amplifier input bias and open-loop output impedance are, is to make an
> >oscillator with a relatively poor integrator. One that satisfies these
> >criterions is the CMOS inverter for example. By choosing that, one actually
> >can make real measurements and actually see the effects of these parameters.
> >(Since a simulation will get you an answer, but not necessarily a valid one.)
> 
> Wow.  Well, if I follow the thread correctly, René, you've done this! (and I
> built [and use] a copy of the circuit).  You put together a very simple VCO
> using a 4069 gate for an integrator.  For what it's worth in this discussion,
> I got 9 octaves of linear operation out of such a "poor integrator".  It seems
> that even a poor integrator is sufficiently accurate for musical use.  For me,
> it casts doubt on whether the other much smaller influences are worth
> investigating at all.

I've had an ASM-1 VCO measure in at a 21 octave range, but the last part wasn't
near tracking since the MAT-02 went into saturation. The integrator was the
standard ASM-1 with a CA3140. I have only done a small attempt to redo the
test, since I didn't have a propper counter available back then. However, for
the low-end I suspect I better clean my board properly.

But a 4069 taking 9 octaves isn't bad, I'd say it about enought for many uses.
It's definitively enought for a toy project thing.

Cheers,
Magnus