[sdiy] Roland DCOs

[Tom Wiltshire]

On 25 Feb 2008, at 12:48, Florian Anwander wrote:

> Hello Tom
>
> Tom Wiltshire wrote:
> > What I wanted to know is if anyone has built a DCO along these  
> lines,
> > and what they discovered.
>
> I did not build a DCO myself, but experimented a lot with the DCOs  
> in the JX-3P. This had two results:
>
> 1.) in general it is more necessary, that the low frequencies have  
> a correct wave shape than the high frequencies. This may be a  
> matter of taste, but the low notes become thin, if the saw is not  
> symmetric, while the high notes still are simply "bright" with an  
> asymmetric wave shape.
>
> 2.) modulating this wave shape is fun, and I do not understand, why  
> Roland missed that possibility. I am not sure, whether the metal  
> cross modulation of the JX-3P uses some changed wave shape cv too.  
> For sure using the DCO1 out as wave shape cv for DCO2 does very  
> interesting results.

Florian,

Thanks for your help, but I'm afraid I don't understand this. The  
ramp wave is produced by linearly charging a capacitor, which is then  
discharged by a reset pulse from the counter. What can be  
assymetrical about this? How can the waveshape be altered?

I'd also be interested to know more about the Cross Mod, as this is  
the part of the circuit that I understand least. The input marked   
_METAL is a mystery to me. The cross mod seems to use DCO1's output  
(which could be noise) to amplitude modulate the output of DCO2. This  
will give an FM-like effect, but with fewer sidebands. Is there more  
to it than this?

Regards,
Tom