MIDI-Retrofit Module
based on t
Reproduced with permission from Paul Maddox

The MIDI-Retrofit-8 started out as a re-release of the MIDI2SDS from Paul Maddox and was called MIDI2SDS (X)
That version, like it's original predecessor, had a limited TRIGGER output range of
around 2V to around 4V. This limitation was imposed on the module as a consequence
of some limitations of the MAX529 chip.

Original schematics and circuit details are here

MIDI2SDS II SchematicMIDI2SDS II FirmwareMIDI2SDS II Gerber Files

NB: These above items cannot be used with the current ELBY Designs offerings



The current revision of the MIDI-Retrofit-8 utilises the MAX528 8-bit DAC which
allows for a wider range of output voltages.
MIDI-Retrofit-8 requires a single-rail supply ranging from 12V to 15V providing for a maximum
TRIGGER output voltage of between 8V (12V supply) and 10V (15V supply).

MIDI-Retrofit-8 supports 2 'trigger modes':-

  1. PULSE Mode where the TRIGGER output is a pulse generated on receipt of a valid NOTE ON message
    and having a pulsewidth defined by the onboard trimpot (between 0.5uS and 120mS),
  2. GATE Mode where the TRIGGER output is controlled by the receipt of valid NOTE ON/NOTE OFF messages.

The logic polarity of the TRIGGER outputs is also selectable:-

  • POSTIVE - the TRIGGER output swings from the low voltage (normally 0V) to the high voltage (usually 5V)
  • NEGATIVE - the TRIGGER output swings from the high voltage to the low voltage

In both cases the maximum amplitude of the TRIGGER output is determined by the VELOCITY value of the respective NOTE ON message as a proportion of the maximum set output voltage.

Settings are common to all outputs.

Accent Mode
MIDI-Retrofit-8 now supports an optional ACCENT Mode. When enabled, the TRIGGER outputs
are paired up 1-2, 3-4, 5-6 & 7-8 with each pair sharing the same MIDI address.
The first output of each pair responds as normal to its associated MIDI message.
The second output will only trigger when the velocity value is greater than 120.

Bill of Materials for MIDI-Retrofit-8 pcb

MIDI-Retrofit-8 software (V4.4)

Build Guide MIDI2SDS-Retrofit Links User Guide

Midi-Retrofit-8 is also available as a 3U Euro-Module - see ED103 in the Panther section of the shop


The minimal installation option is to mount the MIDI-Retrofit-8 inside the unit to be controlled, wiring the TRIGGER outputs directly to the relevant points on the instrument and connecting to a suitable power supply inside the unit. The MIDI-IN socket being the only item that requires to be mounted on the unit for easy access. This option is suited for installations where the MIDI Note assignments will be set once (or very infrequently).

The standard installation optionally brings the LEARN switch out to a user accessible point as well as installing LEDs to indicate the status of each of the TRIGGER outputs. During normal use, the LEDs indicate the status of each TRIGGER output. While in LEARN mode they indicate which channel is beingh programmed. This is useful if you wish to change the MIDI Note assignments often and/or desire a visual indication of the operation of the MIDI-Retrofit-8.

If LED status is required for programming but is not needed for normal operation (or you don't want to mount the LEDs on your unit) the MIDI-Retrofit-8 pcb allows for the LEDs to be mounted on the pcb directly.
These, in conjunction with the onboard LEARN switch, allow the user to observe the
programming status during the LEARN mode.

Installing in to a Roland CR-8000

The MIDI retrofit-8 being used in a Simmons SDSV courtesy of The SImmons Guy


The MIDI-Retrofit-8-1U houses the MIDI-Retrofit-8 module in a lightweight ABS 19" 1U rack
ready for direct rack mounting, or it can just as easily be used free-standing.

The MIDI-Retrofit-8-1U is powered by a 15VDC 300mA power supply (2.5mm DC connector, tip = positive)

Build GuideUser Guide


The MIDI-Retrofit-16 expands the 8 outputs of the MIDI-Retrofit-8 to 16 outputs
so providing control for most larger drum machines on the market.

PCB V1.7 onwards inclueds a new feature - MODWHEEL. Sending MIDI Control Modulation messages (B1, 01, xx & B1 21, xx) to the MIDI-Retrofit-16 will generate an anlaogue output voltage proportional to the modulation value. In the example below, the output voltage has been connected to the HiHat control on an SDSV (scope image at back of video shows the MODWHEEL output).

The MODWHEEL output applied to a Simmons SDSV HiHat courtesy of The SImmons Guy

Current Firmware (V1.4)

Build GuideUser Guide


The latest addition to the MIDI-Trigger family is the MIDI-Interceptor which takes the MIDI-Retrofit-16
and adds a 16-channel Trigger Input Scanner which, in conjunction with new firmware,
allows the MIDI-Interceptor to provide MIDI control of your drum machine in
PARALLEL with the equipments internal controller.
So now you can augment your drum machine by adding your own extra MIDI triggers during a sequence run.

Build GuideUser Guide

Visit this link for examples of the former MIDI2SDS being used to MIDIfy a drum machine

http://www.cykong.com/Synths/Tama TS-305/TamaTS305-MIDI.htm

To implement these retrofits you will need:-

1 x MIDI-Retrofit-8 PCB

1 x MIDI-Retrofit-8 Component Kit.

These 2 items will provide you with the pcb and suffcient components to dress the pcb.
This also includes the MIDI-IN socket and a LEARN switch.
Although not required during normal operation it is recommended that you install
Trigger Output LED's to provide a visual status during the LEARN mode.

Email:  elby-designs@bigpond.com
Copyright 2000. All rights reserved.     Revised: July 2, 2021