Back in approx. 2004 I have received a non working Kawai SX-210 as a gift from a friend. After checking all the supply voltages I have realized it will not be so easy to fix it. I have removed the battery as it has not leaked yet. So due to other priorities I have stored the synth for 13 years in a corner of my studio. 2017 I wanted to hear how it sounds like. Furthermore I killed one key of the keyboard while carrying it through a door - common issue... So I started to fix the synth. After hours with a scope I have figured out the main issues of the synth:
- broken CPU
- several logic ICs were dead
- some traces on the PCB were interrupted
Just a small warning: the used PCB material of the SX-210 is realy fragile. I have not seen something simular before in my whole life. I would call myself not a novice, but I would really refer to an expert in case of any soldering work in this case! Touching the PCB with a soldering iron is most likely damaging the printed pins and traces on the PCB even with low soldering temperatures! For that reason I had to fix a lot of traces by wires afterwards.
The next I have noticed was that several voices were dead or had issues with the envelopes. In this case it is wise to have a closer look on the CD4066 chips in the EG sections on the voice board. In the end I had to replace 4 of them. Now all voices were playing fine. And again I had to replace some traces by wires.
After a friend visited me I wanted to show him the interiour of the SX-210 and lifted up the front panel to have a look. Afterwards the synth was dead again. No! So I checked the chip select lines of the computer board and found a dead trace in a short term of time. After fixing it the synth was up and running again. I played with it in the next 2 weeks and went on holiday for one week. After returning I powered up the synth again - and you guess - not working anymore! Doh!
Now decision time started with two options:
- a) dump the unit as it is in frustration
- b) sell it on eBay as it is
- c) let some time pass by and do something else
Due to the fact I was working on some own synthesizers I have choosen to follow up option c.
Another year has passed and I remembered this little fella still catching dust in the corner of my studio. My thoughts were shall I spend another 200 hours of useless time in order to *try* to fix it, or shall I follow a completly new route.
Now I could start the first line of codes in order to reimplement all the original features. As the main microcontroller has got now theses specs I could also implement some new features: PIC32MZ2048EFG144 main MCU:
- 200MHz (old SX210 CPU had just 12MHz)
- 512KB RAM (compared to 2KB before)
- 2MB FLASH
- SD card slot on the development board
Now it is time to extend the spec list a little bit with some new features:
- MIDI IN and OUT
- storage of patch data on SD card with FAT filesystem for easy backup with a PC
- 4 LFOs (original just 1)
- add sine and random LFO waveforms
- MIDI sync of each LFO
- polyphonic step sequencer supporting velocity per note with up to 99 steps
- arpeggiator (up, down, up/down, random) with 1 to 5 octaves
- MIDI controller support of *all* parameters (RX and TX; by now 95 in total)
- per note control of cutoff by velcoity
- support for longer patch names by using scroll text in the display
- new LFO modulation destinations: HPF and resonance
- pitch bender range up to 99 semitones
- unison detune
- random detune per voice to simulate some detuned old gear
- Modulation wheel targets: cutoff, HPF and LFO gain of each of the 4 LFOs
- 400 memory slots to store own patches
- 12bit DAC for control voltages (10bit before)
By today I managed to realize all of above features. As I do not have any reference SX-210 with an original computer board I was not able to emulate the original behaviour of LFO speed, portamento, glissandro and EG speeds. So old parameter values are most likely not the same as with the original unit. Furthermore the tape interface for storing patches is not supported anymore.
Currently the upgrade is in prototype state. Unfortunately it looks like it will not become a product as further development (bug fixes, bootloader, CE certification etc.) is required. Costs of a final product with very low quantity would be too high to be accepted.
Sound demo: Kawai SX210 Enhanced Demo1 (master).mp3
All sounds are from the SX210 multitrack recorded and SX210 controlled by MIDI. Some reverb and delay added.
