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Subject: Re: [korgpolyex] VCF controls

From: Michael Hawkins <korgpolyex800@...>
Date: 2009-02-03

There are two sample and hold circuits used for controlling VCF.

One is the VCF cut off set point and keyboard tracking. That is output X4 on IC8.

The other is VCF modulation. That is output X5 on IC8.

Yes, all D to A in the Poly is 8 bits (0-255). Amazing it works so well!

Mike

From: Gordon JC Pearce MM3YEQ <gordon@...>
To: korgpolyex@yahoogroups.com
Sent: Tuesday, February 3, 2009 6:21:14 AM
Subject: [korgpolyex] VCF controls

How does the VCF cutoff control voltage get generated?

Looking at the circuit, it seems that the control voltage is fed from
two outputs of IC8, through to half of IC7 forming a couple of
sample-and-holds, then into an odd-looking buffer arrangement.

Is it designed so that one output of IC8 provides fine tune and one
provides coarse tune? I would have thought that 256 steps wouldn't be
enough for a smooth VCF envelope.

Gordon