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Subject: Re: [korgpolyex] DCO2 detune

From: Michael Hawkins <korgpolyex800@...>
Date: 2011-07-22

Gordon,

I want to be able to digitally control the oscillator variation of DCO2. Digital control also might mean using a D2A or use an analog control. Or even a digital pot.

But the goal here is to be able to vary the frequency of DCO2 which gets its "master" rate from the master clock. The master clock will continue to be sent direct to DCO1. And the MG and joystick bend will also continue to vary the master clock rate (thus giving both DCO1 and DCO2 the same MG and joystick bend.

So I want to continue to use the original Poly master clock but want to insert a new DCO2 "detune" that has far more frequency variation and far more granular control than the current detune.

I seem to remember from my electronic engineering classes (that would be 15 years ago now) that a phase locked loop (4066?) might be the way to do this. Does anyone have experience with PLL's for generating frequencies that are slightly varied from the input master clock?

Mike


From: Gordon JC Pearce <gordon@...>
To: korgpolyex@yahoogroups.com
Sent: Mon, July 18, 2011 2:17:47 PM
Subject: Re: [korgpolyex] DCO2 detune

 

On Mon, 18 Jul 2011 00:55:06 -0000
"korgpolyex800" <korgpolyex800@...> wrote:

> Can anyone suggest a way that I could produce a slightly offset oscillation based on a master clock source? And that slight offset could be adjusted using digital or analog signal voltage technique?

Not easily, but you could use a crystal oscillator with a varicap diode to pull it a few kHz. I don't know if that would get you the range you're looking for. Some radios use a transistor and a capacitor to shift the CPU clock a bit. That way, if a harmonic of the clock oscillator will cause interference to a particular channel you can move it out of the way. I'll see if I can scan in the relevant page of a manual that shows this - I know the Motorol MC Micro has this, so if you find a PDF you can maybe do something with that.

If you really wanted to go nuts with it, you could use a DDS chip.

Gordon MM0YEQ