Korg Monotron Eurorack Mod

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Korg Monotron Eurorack Mod
Monotron PCB Front.jpg
Participants Dennis
Skills Soldering
Status Planning
Niche Electronics
Purpose Instrument
Tool No
Location
Cost
Tool category

Korg Monotron Eurorack Mod

Monotron PCB Front.jpg {{#if:No | [[Tool Owner::{{{ProjectParticipants}}} | }} {{#if:No | [[Tool Cost::{{{Cost}}} | }}

What

The idea is to make a eurorack module out of the Korg Monotron synthesizer. The Monotron synths are extremely hackable, Korg released the schematics and a lot of people have published mods. I have the original Monotron. I want to be able to reuse the existing pots and microswitch, so they will stick through the faceplate.

Todo

  • Remove battery terminals from PCB
  • Remove audio jacks?
  • Remove R11, see http://www.timstinchcombe.co.uk/synth/monotron_ref_des.jpg to the left of IC2 under the volume pot. This will disable the ribbon controller but I removed it anyway. The resistor is removed to prevent gates from influencing the pitch.
  • Design and build a board with the desired in- and outputs and controls, probably on protoboard (called I/O board from this point on)
  • Build a simple board for powering the module (called power board from this point on)
  • Design and build a faceplate
  • Assemble everything together and put it in a eurorack case

Thonkiconn mono jack sockets

I will be using Thonkiconn connectors since I've got a load of them and they are easy to work with on protoboard. Datasheet can be found here: https://www.thonk.co.uk/wp-content/uploads/2014/02/Thonkiconn_Jack_Datasheet.pdf

Signal will go on pin 3, and ground on pin 1.

The I/O board

Mono jack inputs

See http://electro-music.com/forum/phpbb-files/monotron_mods_181.jpg for connections of most of this.

Pitch CV in

Controls the pitch of the VCO.

Gate in

Can turn the sound on and off, most probably influencing what's coming out of the Audio out only, not the VCO out.

Cutoff CV in

Controls the cutoff frequency of the filter.

LFO rate in

There is a pad on the Monotron PCB called rate.

Audio in

Possibly use two mono ins and hook it up to the stereo in on the Monotron PCB.

Mono jack outputs

Audio out

VCO out

Connect directly to Monotron PCB, pad is marked VCO.

LFO out

Connect directly to Monotron PCB, pad is marked LFO.

Controls

Switch

Toggles pitch tracking of the filter cutoff frequency

Pitch CV tune pot

Cutoff CV amount pot

Adjusts the amount of influence the CV has over the filter cutoff.

The power board

This will be fairly simple. It will have a 10-pin connector for the ribbon cable to the eurorack busboard. Only 5V and ground will have to be connected to the Monotron PCB. Since the connector has a notch, there is low risk of hooking it up incorrectly but I might decide to have a protection diode somewhere anyway.

Links

 
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