Log to Lin Converter

Magnus Danielson cfmd at swipnet.se
Wed Mar 1 01:03:22 CET 2000


From: keithw at cix.compulink.co.uk (Keith Winstanley)
Subject: Log to Lin Converter
Date: Tue, 29 Feb 2000 13:03 +0000 (GMT)

> Hi all,

Hi Keith!

> a friend of mine want to use his CS30 with other stuff and is after a 
> Log to Lin Converter (maybe the other way too)
> 
> I think Korg had a little box that did this and maybe there was one 
> built in to the MS50?Does anyone have any schems or better still PCB 
> layout for a converter?

We have had this topic not too long ago here on the list, but the quick recap
includes:

Take the expo curcuit out of some suitable VCO. Let's take the ASM-1 VCO for
example (many other will do just as well). Instead of setting up a CCO on the
expo output you trow away the full reset curcuit, you trow away the
waveshapers, you trow away the integrator cap (and high-comp resistor) and
only use a suitable resistor in place of the integrator cap. You may/should
also use a diffrent op-amp. The output of this op-amp will be a V/Hz scale
and the feedback resistor will set the exact scale. The reasoning here is that
the expo curcuit will generate a current which increases linearly with
frequency, it's A/Hz, so now you need a V/A converter, and that you make out
of an op-amp in virtual zero mode and a resistor in the feedback link. The
oscillator uses a cap in the feedback link and this cap is being reset as a
function of the output voltage.

So, in a way there already are alot of schemos available, maybe I should make
one explicitly on the V/oct to V/Hz conversion issue?

Cheers,
Magnus




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