[sdiy] Prophet 08 sub oscillator mod?; DIY Firmware mods; Polyphonic mopho rig

Sun Jan 4 07:56:45 CET 2009

Interesting. However, the mopho is everything p08 is + the sub osc.
Wonder how that works out. They probably use a mixer somewhere...

At the price of this mod, it might pay off more to simply buy eight
mophos. And you get separate inputs AND outputs too. This could become
really good for a guitar synth.

I wonder how receptive DSI would be to the idea of releasing the
firmware source. After all, it's not like it's a crucial business
secret for them. It's just some janitorial functionality happening
there; my thinking is that Dave Smith synths get modified often.
However most of them were (historically) easy to modify, being either
analogue, or having a digital subsystem (for patch storage etc) that
was easy to work out and modify.

Firmware in the new synths is prohibitively difficult for most people
to modify. However, diy firmware modifications would mean that
modifications to the audio path can be interfaced from within patch
storage; and you could expect interesting functionality to be added.
Say, someone could write some sort of nice uTuning support or somesuch
By releasing the source, DSI would simply make their synth appeal more
to the synth diy enthusiast - without really losing anything in the
process. What do you guys think?

On Sat, Jan 3, 2009 at 9:13 PM, ~~~~~ <djhohum at gmail.com> wrote:
> I'm feeling like my previous message must have launched into outer space.
>
> The mopho and the P08 use the PA-397 which is, for all intents and purposes,
> a surface mount CEM-3396. Paul Schreiber provides the  (3396) docs on his
> site and it will give you all the info that you need to know, post DCO,
> about the P08 and the mopho voice architecture.
>
> There are several ways to mix an external signal, like noise or subbass,
> into the 3396 and they are described in the data sheet.
>
> It's of course "possible" on ANY synth, I mean ANY synth, even a DX7II FD
> with a broken floppy drive. That doesn't mean that it's easy or practical.
> Just because they both use the PA397, however, does not mean that it's any
> easier than it would be for other synths.
>
> As far as getting the signal to begin with, it is easier because the 3396
> "DCO" takes a pulse at desired frequency to control the waveshaping. You
> just divide this digital signal by 2/4/whatever.
>
> Getting the signal back into the PA397 is a different ball of wax
> altogether.  There are limitations based on what's already being used and
> whether or not you want to control the levels of the signals independently.
> In short, there are only two independant inputs with level control on the
> 3396 and those are the DCO inputs. Any external signal must either be
> coupled into the waveform converter inputs, the filter capacitor
> connections, or the ouput VCA gain pin. All present some sort of limitation,
> none are just a simple connection that requires no other work to do what you
> need.  Since the P08 has noise, the problem has already been solved in some
> sense but to couple in the sub-bass easily you have to give up noise on that
> voice.
>
> To see how this may not be how the mopho implements it all one has to do is
> think about how to work around these limitations. Since the DCO pulse is
> generated by a dsPIC (AFAIK) it may be possible to also generate and mix, on
> chip, noise and subbass digitally and mix that into the PA397. If this is
> how it's done then it's no easier to duplicate that than it is to reverse
> engineer and rewrite any modern music device code. A non-trivial, ok REALLY
> HUGE project. Perhaps the mopho takes advantage of a more powerful micro to
> generate the DCO, I don't know, I've not looked at the docs, or seen any
> pictures of the mopho.
>
> As was pointed out already (both by me and Ton) the P08 is multitimbral so
> it's MUCH easier to just stack two voices to get this effect.
>
>
>
> On Sat, Jan 3, 2009 at 8:40 AM, cheater cheater <cheater00 at gmail.com> wrote:
>>
>> > 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...
>> hehe, yes, well, it doesn't hurt to foray into dreamworld every now and
>> then.
>> As far as the sub octave goes: mopho does it; it's supposedly almost
>> the same thing as a single p08 voice; i don't see why it wouldn't be
>> possible with the p08 then; i don't suppose they had a special chip
>> made for the mopho.
>> Any idea how that monosynth does it?
>>
>> Cheers
>> D.
>>
>> On Sat, Jan 3, 2009 at 4:19 PM, Tom Wiltshire <tom at electricdruid.net>
>> wrote:
>> >
>> > 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.
>> >
>> >
>> >
>> >
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
>
>
> --
> hohum
>