[sdiy] Roland DCOs

[Oakley Sound]

 > Anyone else want to have a look at the circuit diagram and try and 
tell us what's going on? Please?

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

I think the nMETAL line is simply an on/off control that simply turns on 
the effect. When the line is high the signal from DCO2 goes straight to 
the balance VCA - a crude single transistor VCA, but with two input 
channels to allow for setting the levels of the two DCOs. Also, when 
nMETAL is high, it pulls the base of Q16 low so as to turn it off 
completely.

When nMETAL is low, then 'cross-mod' is engaged. The DCO2 signal no 
longer directly through to the balance VCA but now through another 
simple [Korg style] VCA based around Q16 and IC60b. The control signal 
of this VCA is the output of DCO1 and is now presented at Q16 thus 
turning it on and off with the DCO1's signal level.

Cross-mod is therefore simple AM and not cross mod at all. But then it 
wasn't cross mod on the JP-6 either, just straightforward FM.

The other thing to watch out for on these DCOs is that the pulse width 
of the pulse output is fixed. Not fixed ratio, like say 20%, but a fixed 
time. Thus the harmonic structure changes as you go down the keyboard. 
The JX10 does not a powerful bass monster make. :-)

Tony

www.oakleysound.com