Muff's Modules & More

JP · Last edited by JP on Sun Mar 18, 2012 8:24 pm; edited 1 time in total

Anyone have any experience with the inner workings of an omnichord. Just got one for my looming birthday, and I'm rather smitten with the slightly dreamy ethereal nature of the sound.

Which makes me want to immediately control it with my modular.

With some initial scouting, it looks pretty basic. 3 rows of 9 momentary buttons for the chord choice.

Slide your finger along shorting the circuit sort of keyboard, with what looks like 12 connections (you could replace them all with momentary buttons as well).

So I was thinking.

start with the chords, I'm thinking a perf board mounted 9 jacks wired up to a transitor type of circuit shorting CV driven momentary button push (I think I saw one floating around).

After that apply the same logic to the harp interface, 12 in's with the same very basic remote button pressing circuit.

After that, look into an easy way to pick which scale the chord is selected from.

Does that sound like a sensible plan of attack?

Any other suggestions, words of wisdom?

JP · Posted: Thu Mar 01, 2012 4:19 pm Post subject:

OK, poked around inside. Looks like all the chord buttons are common "ground" for the note, different in for the scale, but not common grounds as you move down the notes, they seem to change 3 times. So i could do 9 trigger ins and each one could have a 3 way on-on-on switch to choose what scale it's in. Or I could do, 27 in's and free up everything (but that's just crazy talk).

The harp section is nice and simple, common ground which you short against 15 possible note traces, and 1 trace which is the magical stop everything button.

So that's the same circuit, but 15 ins.

So now I just need to work out the cheapest way to create 24 "circuit shorting" circuits.

Is transistors the way to go for simplicity. or should I be going with 6 4066 circuits?

RealDudes · Posted: Thu Mar 01, 2012 4:23 pm Post subject:

no answers but it sounds fucking awesome

JP · Posted: Thu Mar 01, 2012 6:26 pm Post subject:

OK, so finally got around to trying out Doepfers gate to s-trigger circuit…

And by Jove it works, and is silly simple, NPN, resistor, jack. I'm tempted to do the full 27 chords & 15 notes.

Quick sanity check but this transistor is good for the job yeah?

http://www.allelectronics.com/make-a-store/item/MPSA13/DARLINGTON-TRAN SISTOR-TO-92-5/.50/1.html

JP · Posted: Thu Mar 01, 2012 6:33 pm Post subject:

12 notes and ground and stop (not 15).

Now trying to work out a logical ans sensible way to get all those transistors, resistors and jacks into a perfboard and wired up to the existing pcb.

Almost tempted to try out eagle and see if I could make a custom pcb to make it easier with a new ribbon cable header.

I think the first bit I do is the notes.

Am i correct in my assumption that ground is common to everything?

How do I find out which side of the switch in the omnichord is the ground side? It'll be the common one yeah?

So wire that trace to all the grounds on the jacks and the middle leg of all the transistors, resistor off the other leg of jack, into each transistor's E leg, C leg attaches to the other trace (1 of 12).

Am I talking crazy talk yet?

j9k · Posted: Thu Mar 01, 2012 10:30 pm Post subject:

It's probably set up like a button matrix with a certain number of strobe lines and a number of input lines

JP · Posted: Mon Mar 05, 2012 7:01 pm Post subject:

Is the resistor nessecary in the s-trig circuit, it works without and I'd like to keep it simple since I need 30 of these, but I'm not sure if it's risky?

JP · Posted: Mon Mar 05, 2012 7:02 pm Post subject:

Also I have a handful of 1-12v LEDs with resistors built in, if I want to wire these to the trigs, do I just short ground to live on the jack?

JP · Posted: Sat Mar 17, 2012 9:46 am Post subject:

NS4W · Posted: Sun Mar 18, 2012 1:52 pm Post subject:

Very interesting project. Have you circuit bent your Omnichord as well? What model do you have?

JP · Posted: Sun Mar 18, 2012 2:37 pm Post subject:

Thanks, just now, started drill holes for the jacks. I'm starting with the strum board section first, then I'm moving onto the chord selection area.

Not circuit bending this one, I love the sound of the omnichord enough without needing more craziness.

Mine is an om27, picked it up for $100 or so on eBay.

http://www.suzukimusic.co.uk/omnichord/om27.htm

numbertalk · Posted: Sun Mar 18, 2012 3:05 pm Post subject:

The strum board on mine isn't as sensitive as I'd like it. Wish I could easily replace it. Following this thread - curious to see how yours turns out.

JP · Posted: Sun Mar 18, 2012 8:18 pm Post subject:

OK, hit a snag, and I'm not sure how to progress.

I have the transistor wired up as per the first picture it's flat side up if it's not too clear.

Which means the pins are from bottom to top:

E, B, C.

yellow and red wires then go to the two points on the board I need to short for the first note to play.

Yellow is attached to the common location. Red is attached to the first pin in header. Each of these pins needs to be shorted to the yellow one.

OK, so this works, trigger out of my modular, and I'm getting a note played.

I do this…

It's peanut butter jelly time!

Then I wire up the next one exactly the same, but I wire the equivilant yellow clip to the first ones yellow clip (thinking to myself everything needs to be shorted to what must be a common ground.) But now I get both notes playing for triggers into both jacks.

I do this…

sad banana

Does anyone have any ideas at all about what I'm doing wrong? I feel so close, and yet so utterly lost.

Edit: also posted on EM since there's a specific circuit benders forum http://electro-music.com/forum/viewtopic.php?p=356683#356683

JP · Posted: Mon Mar 19, 2012 1:36 pm Post subject:

OK, small update. I think I found one issue. The single pin isn't common ground, that's the single "voltage source" the 13 notes pins are the common ground.

It seems if you pipe anything from 5-12v (12v is about what the omnichord pipes in) into any of these 13 pins you get a note.

<warning very hacky about to follow>

So I can actually take the trigger from the jack, ground to common ground (like the ground on the speaker), hot terminal straight into one of these pins, no need for transistors or any of that complex stuff.

I'm completely confused how to do this with transistors now. Just watched a bunch of YT videos on them, apparently the resistor is needed so you don't blow the transistor (ho hum).

Running triggers straight into an omnichord, do I run the risk of blowing up my eurorack? Should I stick a diode in there to stop voltages coming back up the pipe?

<end of hacky stuff>

I still need to do some sort of trigger voltage switching as I just tested the chord switches and they only have 2volts going through them, and it's a lot of connecting point a with point b and point c with point a and point d with point e, etc.

So i still need to either get my head round transistors or maybe look at optoisolators?

edit…

Looking a little better with the transistors, i have a breadboarded multi led controlled by multiple triggers from the eurorack, so just need to apply that logic to the ominchord this evening.

JP · Posted: Mon Mar 19, 2012 6:39 pm Post subject:

Oh shit, it works !!!!

Now for some perf board madness as I solder up 12 of these. smile

JP · Posted: Thu Mar 22, 2012 5:01 pm Post subject:

OK another quick random question.

I just got a batch of LTV-816 IC's in the mail (I ordered them before I had transistor success, assuming the tranny approach was never going to work).

http://www.sparkfun.com/datasheets/Components/LTV-8x6.pdf

I'm curious, I hooked one of these up on a breadboard, does it look like I can feed eurorack trigger voltage straight into one of these IC's?

The spec sheet is a bit fuzzy about what the max voltage/current in is. I have it going through a 10k resistor right now and my test led is blinking away nicely with the euro rack sequencer.

I'm now torn between transistors and optoisolators.