Music and Synth DIY

Circuit bending

Frankenkawai – Kawai K1r – Address/Data line patchbay, LTC1799, display change and joystick addition

A couple of years back, in an early attempt to learn circuit bending, I fried a K1r.

I was doing the old “replace the DSP crystal with a LTC1799 variable oscillator” thing, I didn’t take into account the fact it needs a 3.3v max pulse. I was powering the LTC1799 from a 5v source – and because it clocks at 32mhz maximum, when I tried it over the stock 12mhz or so, the average voltage was enough to fry one of the “unobtainium” proprietary ICs. Gutted, but we live and learn, eh.

I saw someone on Ebay selling a K1 board for a tenner, and a K1 joystick as well. I was originally going to hot air the DAC off the board and swap the fried one out, but it turns out the keyboard version – the Kawai K1 – is VERY similar and fits into the K1r case.

The keyboard has the headphone socket on the back, and the K1r has it on the front of the rackmount – so it needs some flying wires soldered to connect it. Details are in the schematics in the service manual.

The desktop version – K1m – and the keyboard both have a joystick to change the balance between the four parts of a Multi, but the K1r doesn’t.

As this is a now a K1 in a K1r box, I thought I may as well add it. Very straightforward, plugs into the only connector it fits into on the board.

Problem is – the K1 has a “switch” button to turn the joystick on and off. The K1r doesn’t, and it’s off by default, so there’s no way of turning it on without some tinkering.

The Joystick button

To do this, first locate connector CN2. This is the front panel switch matrix. The red wire is pin 1, select line 0. The missing Stick switch needs a momentary push-to-make switch connecting data line PD6 (pin 6) to select line PA2 (pin 3). Cut these wires, solder a new wire to each of them for the switch, and then solder them back together with some heatshrink wrap.

Solder the new wire from PD6 to one side of the switch, then get a 1n1418 or similar signal diode, solder the cathode to the new wire from PA2 and the anode to the momentary switch. Test it – it should bring the Joystick menu up on the screen.

While I was doing this, I thought I may as well jazz it up with a blue display instead of the underwhelming stock one. The commonly available, cheap, 1602A display is available in many colours and is an easy drop in replacement. Bitsbox sell one for £3.

On the top left of the display are the data bus lines, power, etc, and the backlight power is on the right hand side. These are all exactly the same as the stock display – I simply used a hot air gun to remove the connector, and resoldered it along with the K & A wires for the backlight.

From the 1608 datasheet

The only thing that needs changing is the K1/K1r has no adjustable contrast, and the fixed voltage on pin 3 – Vo – makes the display too contrasty.

Just cut the existing wire from pin 3 to the display, then feed it 0-5v from a pot or trimmer wired as a voltage divider between pins 1 & 2 (Ground & +5v respectively) which gives you a contrast knob. Other than that it’s just unplugging one display and soldering the new one in.

Making sure the max clock speed was 12mhz (check the service manual, it migth be 12.8mhz) I replaced the clock crystal with a LTC1799 again, which worked fine. I then added a patchbay for shorting the address and data lines from the Wave ROM (again, detailed in the service manual).

It’s a very usable musical circuit bend and the display looks much better.