[sdiy] Roland DCOs

[Tom Wiltshire]

Hi all,

I've been studying the Roland DCO design, from the Juno series and JX  
synths. These are based on 16-bit counters, followed by a waveshaper  
stage.

There are more details of the basic scheme on my webpage:

	http://www.electricdruid.com/index.php?page=info.junodcos

There's also a pdf (~1Mb) of the JX-8P's voices with dual DCOs up at:

	http://www.electricdruid.com/images/dcos/JX8PDCO.pdf

Now, the major problem with this design is that despite frequency  
being determined by a counter value, you have to supply a CV that is  
proportional to the frequency in order to keep the output amplitude  
constant (IC55 Pin8 DCO1-A and IC53 Pin1 DCO2-A on the JX-8P diagram).


What I wanted to know is if anyone has built a DCO along these lines,  
and what they discovered. I've wondered about doing it myself since  
the 82C54 triple counter chips are only a few pounds and the  
subsequent circuitry is also pretty simple. Alternatively, you could  
use the counters on a PIC or similar.

So, has anyone built a Roland-style DCO?

Thanks,
Tom