[sdiy] Prophet 08 sub oscillator mod?

[Tom Wiltshire]

On 3 Jan 2009, at 15:26, cheater cheater wrote:

> Wow, synth porn.
> At least you know how your enemy looks from the inside... or  
> something.
>
> Tim:
>> Adding the hardware to create sub-octaves: big job
> What are you basing this on? Is there a schematic you are following?
> What would be involved?

You need a minimum of a flip-flop per oscillator (at least 8 dual  
flip-flop chips - 4013 or similar). You also need a way back into the  
output VCA. This might be the more difficult part, since there is no  
guarantee that this input is available on a pin. It may be internal  
to the DSI voice chip (top of the photo). There's loads of sub- 
oscillator schematics available you could use; the SH101 has a nice  
one, or the Korg Poly6 is another example.

>> Reverse engineering and reprogramming the operating system and  
>> adding the
>> hardware to allow control of the suboctaves: HUGE job.
> Oh yes, definitely.
> But on the other hand, we're talking about a simple uC program here.
> This isn't a supercomputer. People have reverse engineered bigger
> things; the problem is that ASM isn't as popular nowadays, so if you
> run into trouble, you might be hard pressed to find someone who knows
> what to do :)

Reverse engineering will be made even harder by the fact that you  
won't be able to get even the assembled code out of the uPs. It'll be  
code-protected. So instead you've got to write code that will do the  
same job from scratch without knowing anything about the hardware  
beyond what you can see.
It's a tiresome way to recreate work that Dave Smith has already  
done. But you'd have a cool custom Prophet at the end of it...

T.