Midi to CV converter with 32 CV Outputs - 4x AOUT_NG´s ?

[mangor]

Hello,

I need some help,

I wanna build myself a midi to CV converter which should have at least 32 CV outputs.

Probably the only way to do that is 4 x individual MIDIBOX CV with 4x AOUT_NG´s plus 4 x Cores , ... i am right ?

Or is it possible with one Core and split to 4 AOUT_NG´s ?

thanks,

[Max Romantschuk]

1st commandment of midiboxing: Read the confusing documentation.

2nd commandment of midiboxing: Read the now slightly less confusing documentation again.

According to the MIOS introduction page:

http://www.ucapps.de/mios.html'>http://www.ucapps.de/mios.html

...a single core can handle up to 64 analog outputs. I'm sure the exact module configurations can be found with a little more research. :)

http://www.ucapps.de/

http://wiki.midibox.org/

[bugfight]

you forgot "Don't misquote technical information"

that's 64 analog inputs.

pic core is probably not up to the task of 32 cv outs, but core32 should be...

[Max Romantschuk]

you forgot "Don't misquote technical information"

Indeed. My fault entirely. Must be the fever... Stupid viruses. ;)

[SLP]

SHX8-Module?

[Max Romantschuk]

Back on topic... Looked through the docs once more:

http://www.ucapps.de/mbhp_shx8.html

"The MBHP_SHX8 module expands MBHP_AOUT to up to 64 CV outputs. It consists of 8 Sample&Hold chips which multiplex the analog outputs of the MAX525. Please note that this module requires special support from the application which is not possible in all cases."

Copy-pasted this time... Less risk for my disease-ridden brain to fsck with me... :)

EDIT: And I'm too late. ;)

[bugfight]

chips unobtainium.  but i did wonder why this could be supported but not 4 aout modules...

[seppoman]

but i did wonder why this could be supported but not 4 aout modules...

That's because you didn't extend the MB CV software to support that feature yet  :P

but seriously, I think it should be not too much of a problem to service 4 AOUTs from MBCV as this software has relatively few things to do in real time (compared to e.g. MBSID), so the PIC probably has plenty processing power for supporting more than one AOUT module. That app only isn't really in the center of focus for most people here (including TK), so nobody worked on these features yet.

"It's a dirty job but someone's got to do it" ;)

S

[nebula]

I've been pondering this for a while.

There's got to be some sort of hardware solution for multiplexing analog outputs, that could probably work equally well with AOUT and AOUT_NG.  Most vintage polysynths, which have dozens of internal CV targets, have only a single multiplexed DAC to handle the work.

Certainly the best choice from an economy perspective would be to multiplex before we start to add additional AOUT* boards.  Maybe it's not worth the effort, since it would probably be easier to extend MBCV code to support a second (or third or fourth) 8-channel DAC.

[bugfight]

yeah sep, it could be i was just remembering this factoid from the context of mb-sid or mb-seq.  it could also be that the diminished update rate of s&h can't really be improved on by using multiple aouts.

and neb, the sample and hold module already does this multiplexing, it just needs to be redesigned for obtainable s&h chips.... (which will also probably go obsolete)

[seppoman]

the sample and hold module already does this multiplexing, it just needs to be redesigned for obtainable s&h chips.... (which will also probably go obsolete)

Well I researched the still available S&H ICs during the design process of the AOUT_NG and there are not many options. If the replacement module should stay at least somewhat affordable and similar size, it narrows down to the AD SMP08 http://www.analog.com/static/imported-files/data_sheets/SMP08.pdf. That's the only 8 channel S&H that has 1 to 8 multiplexer, output buffers and hold capacitors already integrated (i.e. doesn't need any supporting cirquitry). It's listed as "production" at AD, available lead free (which means they don't intend to drop the model very soon or else they wouldn't have ported it to the lead free process), at least the SOIC version is available from Digikey and Farnell for 12-16 Euros. So a 64 channel module would be around 100 Euros just for the 8 ICs.

I see the point of a S&H module for the 64 channel people, but I'm still not convinced people who need 24 or 32 channels wouldn't be better off with chained AOUT modules. The SMP08 is about the same price like the NG DAC and if you don't stuff the parts for the bipolar option, the rest of the module is quite affordable, without adding extra errors of S&H to the output CVs (I guess about 10 mV).

The main problem that needs to be adressed first is that the MBCV firmware doesn't support more than 8 channels. Before that is changed, I don't think it would make much sense to work on a redesigned S&H module. If someone wants to work on the software side and does own more than one AOUT/AOUT_NG, chaining them is quite easy, both software and hardware-wise, so I'd suggest using chained modules for a start. When (or probably better: if) the software part is settled, I'd be glad to do a nice layout with the SMP08... :)

S

[stryd_one]

Just to support the above, I talked with seppo during his design phase of the aout_ng about multiplexing and I know he really did his homework.