Category Archives: Synthesizer

KORG M1 realtime control

I never thought I´d ever own a KORG M1. But when I recently found a used one at a very reasonable price I couldn´t resist. Now I am not really interested in its famous piano or organ sounds, or the internal sequencer for that matter. I rather want to explore its capabilities to produce drone like soundscapes. And for that, at least a little amount of realtime controllability would be apreciated.
Fortunately all relevant parameters are editable via SysEx. And as I found out the M1 reacts fluently to parameter changes. The only oddity is that the parameter numbers in the SysEx message depend on the structure of the program, and so double oscillator programs have a different parameterset than single programs. I therefore settled for a control set for double oscillator programs as polyphony is not an issue for me. The fact that the display of the M1 also jumps to the currently modified parameter is a nice touch as well…

DW-6000 editor panel for Ctrlr

I have just released a panel for Ctrlr for the KORG DW-6000. This panel can be used as a mapper between standard MIDI CCs and the DWs SysEx messages, allowing all parameters to be controlled by a hardware MIDI controller. This also applies to those parameters that are combined in a single SysEx message, like OSC 1+2 waveforms.
A corresponding preset for the BCR2000 MIDI Controller is also in the works…
You can find the Ctrlr panel here.

CS15D channel 1 modification

Since I got my CS15D I´ve always known that one day I would make a certain modification to it, and this day has finally come: Manual control for channel 1.

Mod design

When I opened the synth the first time I was pretty surprised by what preset meant before the time of (affordable) digital memory! Each preset is a set of resistors defining the CV values of the parameters.
The channel 1 and 2 presets reside on distinct PCBs.
I eventually managed to grab a copy of the service manual, and it made it pretty obvious that it would not be too hard to replace the presets by controls. The service manual reveals that all parameter CVs use the same 10V voltage source. The preset selectors route this source to the respective preset subcircuit. Channel 1 manual mode is not so much different. The voltage source feeds the control pots that are buffered by op-amps.

CS15D manual control subcircuit

CS15D manual control subcircuit

The overal design of the synth proved execellent for the modification.
The preset selector switchboard can be easily unscrewed from the front panel and the panel slits provide enough space for the new pots.

CS15D preset switch panel

CS15D preset switch panel

The preset board for channel 1 can also just be unplugged and taken out, and the board connectors reused to feed and source the modification board.

CS15D channel 1 preset board

CS15D channel 1 preset board (PM1)

This design makes it easy to replace the original components with the custom control modification without altering the original circuits or messing up the front panel.

Now the modification was pretty straight forward:

  • Build a PCB with the driver op-amps, voltage source routing and board connectors.
  • Build a control panel

It was not so complicated, but a lot of soldering work..

Once finished, I hooked it all up, switched on the synth and… It worked!
But just for a short time, which brings me to….

The Tr7 problem

A minute after I started calibration works on channel one, a flashy bang to my left silenced the audio output of the CS15. After a short notion of anger and a little fear I might have damaged an irreplaceable custom chip, I searched for the fault and located it soon: A transistor blew into pieces. Lucky enough the marking on the front was still readable, and a glance at the service manual revealed the function of the destroyed part. Tr7 on the VCO board is the actual 10V source for the preset circuit, regulating +15V from the main power supply down to 10V.

I first assumed I caused a short circuit while calibrating which lead to the destruction of the transistor, so I simply replaced it with a new one and went from there. Not long though till the replacement gave up, too. So obviously my modification lead to an overload. I replaced the voltage source for my mod board with a power supply generator, which told me my circuit draws ~30mA. The transistor provides a base-emitter current of 150mA, so my assumption didn´t seem so far fetched.

I then decided to include an 7810 voltage regulator into my board, feeding it directly from the main power supply. And what can I tell you… problem solved!

Summing up

Yamahas design for the manual controls has a very handy side effect. The driver op amps can also work as CV mixers. So you can easily hook up an external CV input in parallel to the control pot for each parameter. Due to space limitations, I did that for pulse width, filter cutoff and resonance. Now I can feed in an LFO from my modular, too. But this also leaves some space for improvement on my circuit. The eurorack modul CV voltage is in the 5V range. The CS15D works with a 10V range. So I still have to include amplification for the incoming signals…

The happy ending

The mod works and I am very happy with it. I am not so much a fan of presets anyways and it never made sense to me to create the sound of a trumpet or clarinet with an analog synth. So now I have a brilliantly sounding synth with two manually controllable channels.

For the below video I hooked up MFBs Urzwerg to each of the channels CV/Gate inputs (via a CV converter of course) with two slightly different sequences. One channel plays the bass part and the other one the melodic part. In addition to the sequence I recorded two solo melodies.
Yamaha CS15D modified from MacroDX on Vimeo.

DW-8000 control via SysEx

The lack of hardware controls on the device can be overcome by using a MIDI controller capable of sending System Exclusive messages. Almost every parameter of the DW-8000 can be controlled via SysEx. Only the MIDI settings themselves and the arpeggiator are excluded.
I am using the Behringer BCR-2000 controller for realtime tweaking. If at all, the only setback is the coarse resolution of the parameters on the DW which does not even make use of the full MIDI value range of 128 steps. But the simple fact that it is fully controllable (other than its little brother, the DW-6000) totally makes it up to me.