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 Forum index » DIY Hardware and Software » Circuit Bending
CV Retrofit an Omnichord
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nomeist



Joined: Mar 19, 2012
Posts: 5
Location: NJ

PostPosted: Mon Mar 19, 2012 6:30 am    Post subject: CV Retrofit an Omnichord Reply with quote  Mark this post and the followings unread

I had posted this over on Muffs, but figured this forum might have more specific knowledge. Muffs post is here http://www.muffwiggler.com/forum/topic-54155.html

Quick overview. I have a Suzuki Omnichord that I'd love to retrofit for CV triggers for all the buttons. My plan is to do all of the strum pad and all of the chord bank, so it's 25+ triggers.

So i'm starting slowly with the strum pad.

The strum pad connects to a 16 pin header, 1 is a common "ground", shorting 14 of the pins to this plays that note of the strum section, you can connect more than 1 pin at a time and it plays both notes. The 15th pin is the sound kill switch.

My play was to use the transistor as a switch method. So put 14 jacks on wired to transistors so that a trigger pulse generated by my modular synth would act like a switch and short the pin to the common.

Last night I started trying out my plan, and I can get 1 note to work using the below layout (please excuse my scary test setup, the final thing will be soldered and pretty looking).

I can get trigger to generate a note - hooray!

The issue I'm having is if I try and hook up two using the same format, and I connect the common "ground". I now get 2 notes for every trigger into either jack.

I'm almost wondering if I have my ground backwards. Or my transistor backwards.

Two attachments below show the trany setup and the corresponding header connections. Yellow is the common connection.

In the first image my transistor is wired up I have the transistor wired up flat side up if it's not too clear, which means the pins are from bottom to top:

E, B, C.


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nomeist



Joined: Mar 19, 2012
Posts: 5
Location: NJ

PostPosted: Mon Mar 19, 2012 11:37 am    Post subject: Update Reply with quote  Mark this post and the followings unread

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>

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>

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?
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Mongo1



Joined: Aug 11, 2011
Posts: 411
Location: Raleigh NC

PostPosted: Mon Mar 19, 2012 2:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

It's late in the day, so my thinker might now be thinkin so good, but I was a little confused about something.

Are you trying to use the omnichord to as an input device, so that it supplies triggers etc to your eurorack, or are you trying to go the other way, so your euro can 'play' your omnichord?

Gary
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nomeist



Joined: Mar 19, 2012
Posts: 5
Location: NJ

PostPosted: Mon Mar 19, 2012 2:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Mongo1 wrote:
It's late in the day, so my thinker might now be thinkin so good, but I was a little confused about something.

Are you trying to use the omnichord to as an input device, so that it supplies triggers etc to your eurorack, or are you trying to go the other way, so your euro can 'play' your omnichord?

Gary


Euro trigger sequencers out to play the omnichord. Basically so I can "program" it as part of a pattern.

There are 2 bits I'm really excited about:

A: using the A-152 which has trigger outs corresponding to a CV, throw slew on the CV you get the same effect as sliding your finger across the strum panel.

B: programming triggers for base "strum patterns" then clocking different pattern for the chord progression. So you keep bang in sync play with buttery chord changes (chord changes could even be off tempo to really mix things up.
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Mongo1



Joined: Aug 11, 2011
Posts: 411
Location: Raleigh NC

PostPosted: Mon Mar 19, 2012 2:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks - I understand now - I assumed you were trying to go the other direction.

So for the strum bar it sounds like it might be as simple a rigging a small value of resistor and a diode on each pin. The cathode point toward the omnichord and the anode toward your synth. I would suggest trying that on one or two pins and see how it works. If it seems ok, go for the rest of them.

That chord section sounds like it will require some work though. I'm a bit hampered by my complete lack of knowledge of how the omnichord gets things done. Have you run across a schematic of it ?

Gary
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nomeist



Joined: Mar 19, 2012
Posts: 5
Location: NJ

PostPosted: Mon Mar 19, 2012 2:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nope haven't been able to find a schematic.

The chord and the strum sections are really very basic. They both use (for want of a better term) simple momentary switches. For the chords they really are momentary push buttons, if you short two points on the circuit at the base of them the chord changes.

Strum is a little more complex, but still just a basic short (common voltage to 1 of 14 "grounds" - no idea if those terms make sense).

Right now I have a working bread boared and multi transistor CV controlled LED's. So I'm using that as my starting point. Just now apply it to both situations on the omnichord and see if I can get it to work.
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nomeist



Joined: Mar 19, 2012
Posts: 5
Location: NJ

PostPosted: Mon Mar 19, 2012 4:42 pm    Post subject: Reply with quote  Mark this post and the followings unread



It lives !!!

Now time to put 12 of these on perfboard. Damit Transistors are a pain on perf, especially if you need access to the middle leg.
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Kent



Joined: Mar 31, 2008
Posts: 53
Location: All over Europe & elsewhere (Mostly Paris)

PostPosted: Wed Dec 19, 2012 1:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm bumping this to the top as I'd like to know how the experiment developed and whether it was a success.

I'm absolutely in love with my Folktek modified OM-84 and am thinking of bending an OM-100 or higher. I have schematics for the OM-84 if anyone need them and I'd like to confer with anyone who has had success in bending these beasts; especially the Original Poster as I'd like to work in some sequencing and beat-layering.
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