KAC TM62100

Midi and more for Yamaha SK synthesizers

Description | User Manual | Installation Manual | Order online


TM62100 adds MIDI and additional features to SK15, SK20, SK30 and SK50D synthesizers. It is a direct replacement for the Yamaha YM62100 / YM621 key assigner and can also be used to replace defective original ICs – even when midi is not required. The original behaviour is fully maintained.

TM62100 might also work in organs such as Yamaha D85, please read these notes.


  • MIDI input and output on several channels with optional soft-through
  • Independent midi control of upper keyboard, lower keyboard and pedal sections
  • Full tonal range in split mode
  • Midi filter cutoff and resonance control
  • Additional filter LFO
  • Midi sustain control
  • Midi portamento control
  • Midi aftertouch
  • Note priority for the pedal/BASS section: Lowest/Last/Highest note
  • Built in configuration menu can set midi channels and other parameters.
  • Non-destructive installation can be reverted to original

User manual

A complete user manual as PDF can be found here:
KAC TM62100 User Manual

Midi note control

Depending on the synthesizer, the various sound generators can be controlled independently via midi. Typically these are arranged into the same “synth-groups” that exist in the original synthesizers. Each group has its own midi channel configurable using the built in config menu.

  • SK15: All sounds on Group 2 *
  • SK20: No split mode: Group 1 plays organ, poly-synth and strings. In split mode: Group 1 plays Organ (all 61 notes), Group 2 plays String and Polysynth (All 61 notes)
  • SK30: Same as SK20, but SOLO-Synth plays on channel 2 in NORMAL mode and channel 3 in BASS mode.
  • SK50D: Group 1 plays the lower keyboard, Group 2 plays the upper keyboard. BASS Plays on Group 3. Depending on settings, SOLO SYNTH plays on Group 2 (NORMAL) or Group 3 (BASS)

* In case of the SK15, it might be possible to re-route the organ section to Group 1 by modifying the circuit. This has not been tested yet.

Additional midi control

If applicable, the following parameters can be controlled additionally:

  • Poly-synth filter cutoff (All SK-Synths), with additional LFO
  • Poly-synth filter resonance (All SK-Synths) *
  • Sustain ON/OFF (SK20, SK30, SK50)
  • Solo synth filter cutoff (SK30, SK50) *
  • Solo synth Aftertouch (SK30, SK50)
  • Solo-synth Portamento ON/OFF (SK30, SK50)

* For the synths with built in SOLO section, it is possible to control Poly-Synth resonance OR Solo-Synth cutoff, but not both. This is a choice you need to make during installation.

Additional Filter LFO
An additional filter LFO is accessible via midi CC controls.

  • Frequency range: 0.1 Hz – 1000 Hz
  • Free running or midi sync with adjustable divider
  • Triangle, Saw, Inverted Saw, Square and Random waveforms

Audio frequency modulation is possible and can create novel sounds usually not possible with the SK-series synths. Warning: At high frequencies, the LFO signal may be audible. This is due to the filter IC suffering from some amount of CV bleed-through.

Midi output

TM62100 features midi output on several midi channels. The various synth-groups (see MIDI input) also apply here. This means the upper, lower and pedal keyboards can send on different midi channels. In split mode the two parts send on different midi channels as well. The channel numbers can be set in the config menu, as well as individual output channels turned off.

MIDI Soft-through
Optionally MIDI soft through can be activated using the config menu. Incoming midi messages will be merged with the internal midi data and forwarded to the MIDI output.

Configuration Menu

The built in configuration menu can be used to set parameters such as midi channels or the pedal note priority. It can be accessed turning the synth on while playing an D-minor chord.
The user manual explains this menu in detail.


Installation is relatively simple, but requires soldering and drilling holes for the midi sockets. We have a list of synth techs who can help with the installation.
TM62100 replaces the original YM62100 IC. The original IC needs to be desoldered and a socket put in place. TM62100 is then put in the socket. Holes for the midi sockets need to be drilled and the sockets installed. A stencil for drilling is part of the kit. In order to get additional midi control (e.g. Filter), a few wires need to be soldered to the synthesizer’s PCBs.

Complete installation guides are available as PDF for:

Yamaha SK15 TM62100 installation guide*
Yamaha SK20 TM62100 installation guide
Yamaha SK30 TM62100 installation guide
Yamaha SK50D TM62100 installation guide

(* no guide yet, but we can give pointers, please contact us)

TM62100 also works in organs that use the YM62100 IC, such as Yamaha D85. However, the “AUTO BASS CHORD” functionality is not implemented and will not work. According to a customer, the following features do also not work in the D85 after installing TM62100: SPECIAL PRESET – Only Piano and Guitar work, CUSTOM VOICE: lower keyboard only, Synchro Start does not work, Auto Arpeggio” and “Rhythm Chord” do not work.

There also is a YM26100 (not 62 !) IC used in various Yamaha organs. These are not compatible.