Korg DSS-1
Sometimes I seem to attract interesting old electronic instruments. Around 2008 I came across an almost-working Korg DSS-1 keyboard. The DSS-1 was one of the first keyboards to incorporate digital sampling and combined digital and analog effects. It is also an interesting mix of old and new. It has a distinctive sound that is still good even today; but that is combined with a klunky user interface and a 3.5" floppy drive for storing instruments. Like the Rodgers organ before it, I fixed the keyboard up and passed it on to someone who can hopefully make use of it.
A couple of words about the instrument
It is amazing how fast technology can move. The Rodgers organ, made in the late 1970's, was driven entirely by discrete analog components. The DSS-1, released less than ten years later (1986), is processor-controlled, uses digital samples, and has a MIDI interface. The inside is pretty packed with electronics. On the left are a few circuit boards containing the brains of the instrument. The power supply is on the right. Several circuit boards are mounted on the lid of the instrument that hold switches, sliders, and a small backlit LCD text display. (The photo at right shows the instrument with the lid opened upwards so that all the circuits are visible.)
The DSS-1 has two CPUs that share duties in running the instrument. There's an Intel 8085 that handles the more administrative tasks and digital I/O (floppy disk, buttons, etc), and a Hitachi 63B03X microcontroller that handles analog I/O, MIDI, and directly controls the synthesis circuits. Controlling the instrument from its control panel is pretty clunky. There's a small text LCD display and a couple dozen buttons on the top surface that let you navigate through all the functions of the keyboard. Most of the top of the instrument is covered in descriptions of the various menus in pretty small type. There's no permanent storage in the keyboard; all instruments are stored on specially-formatted 3.5" floppy disks. You load instruments into memory one 'system' at a time. Each system holds several instruments, so you can switch between instruments quickly without reading from the floppy disk each time. (Floppy disk I/O is as slow as you would expect.)
Two useful links:
Glen Stegner's site contains a number of vital DSS-1 resources: images of the original instrument floppy disks, a utility for creating the disks on a PC (assuming you have a PC with a floppy drive!), MIDI information, etc.
Tom Virostek has created an upgrade for the DSS-1 that increases working memory and makes a number of other enhancements. I just discovered his project and I'm fascinated. If I still had my DSS-1 I would be bugging him every other day to see when his latest revision would be ready...
Button replacement
The most severe problem my DSS-1 had was a number of non-working buttons on the top of the keyboard. The most important failed button was 'enter.' When that button doesn't work, you can't tell the keyboard to load an instrument from the floppy disk, so the keyboard can't make any sound, period! My guess is that's why the previous owners were trying to throw the keyboard away. Happily, it was an easy problem to fix. The switches are standard microswitches, and are easy to desolder from the single-sided circuit boards that hold them. The only trick is to make sure the replacement switches are the same height. I first tried to use some switches that were about 1 mm taller than the originals, but when the boards were screwed back into place the switches were jammed in the 'on' position. All the wires to these boards are terminated by headers, and each header has a different size, so there's no question of connecting things incorrectly when putting it all back together.
Joystick replacement
On the left side of the DSS-1 is an analog joystick. Its x-axis is used for pitch bending, and the y-axis controls other analog effects. On my keyboard the joystick was busted -- it looked like something heavy had been dropped on it, breaking some of the plastic pieces that held the stick in place. In the photo at right, showing the underside of the original joystick, the locknut at the bottom and the washers under the brass strap in the middle were my attempt to piece the joystick back together. That didn't work, so I made a replacement instead.
I wasn't in a place where I could machine any components, so I bought a joystick instead of trying to build something of my own out of individual parts. I used a 252 series mini-joystick by CTS (from Digikey). The main problem with the mini-joystick was that it was, well, mini. I built up a little platform using perfboard and spacers to hold the joystick in the proper location in the cavity of the original.
Now some electrical fiddling around was necessary. The potentiometers in the original joystick had four leads, rather than the usual three. The potentiometers operate between 0 and +5V, and the fourth lead provides exactly 2.5V to an extra contact in the middle of the potentiometer. This served to provide a little deadzone in the middle of the joystick's movement and to ensure that it provided a neutral voltage when the joystick was centered. Nowadays this would be taken care of entirely in software, and I couldn't find joysticks (or any potentiometers at all) with the fourth lead. To try to imitate this behavior I built the circuit shown at right. The diode and resistor networks provide a bit of nonlinearity, and the op-amp makes sure the voltage output covers the full 0 to 5 V range. I don't recall exactly what components I used, but any dual op-amp with rail-to-rail output that can run on 5 V would work. The diodes were plain old silicon diodes, fairly low power, but all four of the same type.
To finish it off, I make a nice little wooden handle for the joystick. And it worked pretty well!
And that's that. I had the DSS-1 while I was going to grad school in Minneapolis. When I moved away I left it in the hands of an artist friend who might have a chance to use it to do something creative.
