Stompbox and Midi Question

[simspace]

Hi all,

I'm just completing my first stomp box - a kay fuzztone. And I am hooked. Tons of fun...

I really would like to build several classic analog stomp boxes that can be midi controlled.

Let me explain, using a boss SD-1 pedal as an example...

Instead of three pots (Level, Tone and Gain) that have to be manually adjusted, I'd like to send MIDI messages to adjust level, tone and gain. At first I thought of using motorized pots. But, couldn't I use some form of variable "digipot" to do the same thing?

Why do I want to do this? My entire guitar rig is based on the Voodoo Labs Ground Control Pro (GCP) and two Voodoo Labs Audio Switchers which I love!

I can switch stomp box combination's easily, but I still have to manually adjust them. I'd like to use midi messages to do that.

Why not use a stomp box modeler? I do. The Line 6 M13 is great. But I also use several analog stomp boxes too. There's just no substitute for a classic stomp box!

So to sum up, I want to...
1. Build several analog stomp boxes.
2. Place the several circuits in a blank 19" rack enclosure instead of individual stomp box enclosures (imagine 3 or 4 rack mounted stomp boxes in one enclosure).
3. Hook them up to my GCP / Audio switcher system to select several stomp box combination's.
4. Send midi messages from the GCP to one or more stomp boxes to adjust their settings per song during live sets.

I assume each stomp box would need some front-end midi component that acts as an interface between the GCP system and the analog circuit.

Any ideas, advice or direction you can offer would be great and really appreciated.

Thanks!

[Processaurus]

http://highlyliquid.com/kits/mpa/

I've wanted to make some midi controlled analog effects with this kit, not sure what would be best, maybe a midi controlled fuzz factory, so you can save all your settings in your sequencer.  Something with touchy/interactive controls or a variety of sounds where they're hard to reproduce quickly.

This same kit can sync CMOS logic to MIDI, at some point I'd like to hopefully incorporate one into an analog sequencer pedal of some sort.  It could probably be used to sync a tap tempo LFO chip like the molten voltage one or the electric druid PIC based design.

[Processaurus]

With that kit they wouldn't have knobs though, it would be strictly midi messages controlling the digi-pots.  It would be a much more complex and less documented project to have real knobs and midi controlling the same parameters.

[MoltenVoltage]

Digi pots are really cool, but the max current from one I just checked out
http://ww1.microchip.com/downloads/en/DeviceDoc/11195c.pdf
is 1 mA at the wiper

I haven't built much distortion, but I am guessing that the pots on most distortion pedals pass more than 1 mA, right?

Has anyone measured the current at Level, Tone, and Gain pots across the whole range to find the max current?

I'm thinking you'd need another transistor stage to control the circuit current.  Once you got it all worked out, it would be really cool.

[thereverend]

i've never messed with them myself but i have seen people do lots of clever things with arduinos.

[simspace]

Thanks for your replies! I'll check out those links.

[GroovyMan]

I had a similar idea. To take it futher you could have "dockable" pedals that could be taken out of the main rack controller and replaced with other effects. The pedal could also be taken away to another pedal board and be used on its own.