Korg Poly800/EX800 Users

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