Fun Stuff - K2000

Kurzweil K2000


Introduction

After buying my K2000S I bought the Technical Reference Manual and schematics (available from Young Chang) to see just how the unit works and what mods may be possible. It turns out to be a really great machine to customize, if you are up to it. So read on to get a feel for what you can do! Also, I hope you can benefit from my experience with investigations of the NVRAM, SCSI termination, and the liquid crystal display, etc.

All About the Display

The liquid crystal display, or LCD, doesn't seem to be bright enough for the most of us. Some of this is due to the fact that it's backlight has a limited lifetime (about 2000 hours if I remember right). The backlight is electroluminescent, like the EL nitelights of years past. Unfortunately there is no "backlight" switch on the unit (except for the main power that is). So if you leave your synth on all the time you are reducing the EL backlight's efficiency over time. All is not lost if your display is dim however! First of all, the display is perfectly readable with an external light source - like a small booklight or whatever shining on it at an angle. In fact, you might like the unit better with the EL panel supply disconnected! This removes the blue from the background and gives you better contrast with the liquid crystal characters (with an external light source). On my unit there is a twisted pair of rather large white wires connecting the display backlight and the power supply. Disconnect this and see what you think.

Ok, your EL panel is shot and you want a new one. From what I understand, you don't have to buy the whole display and EL panel - you can just buy the EL panel by itself (but not from YC)! So here are some of the necessary part numbers for you:

The LCD has an embedded Toshiba T6963C controller. If you investigate lcd's from other vendors you need to find one with this controller on board or it won't work. The display is connected to the synth with a ribbon cable, making it simple to try replacement displays without taking the whole unit apart. I have found the "W" part surplus for less than $30.

To be honest, I don't know which backlight is on the standard display - I suspect it is the blue-green one. You should be able to order this part from any of Sharp's distributors - here you have to approach one of the local electronics distributors; those who typically sell components to local original equipment electronics manufacturers (OEM's). Companies like Pioneer, Newark, Wyle, Hamilton, might be candidates. Sharp has a fax line that might be able to provide you a list of local reps/distributors: 1-800-833-9437. You can also get the spec on the display there. The cost of the EL panel should be less than $50, maybe less than $30. Unsolder the 2 wires to it at the display and the backlight just slides out! Slide another in, solder, and you're done. Getting AT the display IS kind of a bitch, as you have to remove the pcb mounting screws above it and move the synth board(s) up out of the way to get to it. Label and map out the ribbon cables beforehand as they sometimes come out on their own. While you are at it maybe you want to replace the red panel led's with blue ones(?). I've haven't attempted it but it would look cool eh?

I have located some additional vendors of seemingly compatible LCD's. These may have brighter backlights - at least one of them had an LED and CCFL (fluorescent) backlight option - thing is, my display is fine, and I don't feel like spending the bucks to find out how the others work out. I had intended to sell an LCD or backlight replacement kit but maybe you guys can get by with the above info alone.

Voltage Control Inputs

Here's the fun part! The K2K has several inputs that can be used as voltage control inputs for modulation and linear voltage control of programmed settings! The modulation wheel, the pitch bend, the control pedal, key pressure, and the data slider, are all voltage inputs read by an analog to digital converter. The control pedal input is an obvious target, but you could add one or multiple normally closed input jacks to accommodate more than one voltage source. All of these expect 0-5V signal levels. With the control pedal, the tip is the input, the ring is sourced 5V (appx.). The pitch and modulation levels are actually negative signals inverted by op amps so they might be a little tricky to interface into. The control pedal and data slider inputs are direct through though. So go ahead - connect up a breath controller, a ribbon controller, percussive triggers, or whatever and have fun with it! The ADC speed seems quite reasonable even for filter or pitch modulation.

The NVRAM (Toshiba TC518128AFWL-10LV)

This beastie is probably why my unit occasionally comes up with no output, no modulation wheel, one channel missing, etc. The NVRAM is used to store your programs, using the battery backup. Instead of using SRAM, the synth uses pseudostatic ram. This isn't used much anymore. I think at the time it was a relatively inexpensive attempt at long term data storage that didn't take the power that dynamic ram (the simms) uses. Yes, this is what drains your batteries down. Now, technology has advanced to the point where you can get SRAM with built-in battery etc. In any case, SRAM is much higher capacity now and may be a good candidate to replace the existing part. One problem with the existing part could be that it has internal circuitry that refreshes the memory bits even while the synth is off. This is supposed to go on when it is safe to do so. Problem is that there isn't much in the synth to sense the power supply voltage(s) dropping below recommended levels. So garbage may get written to the NVRAM. This is why sometimes you have to take the batteries OUT for 15 minutes or so to fix a problem. I'd like to put in a power fail detect circuit and a SRAM and see if my problems go away.

The PRAM Option

The PRAM option is more of the NVRAM chips on a card with a PAL for detection and addressing control. Such a small amount of memory shouldn't cost as much as YC is asking. As these too draw battery current while AC power is off, you will have to replace the batteries more often with this option installed. Nothing wrong with your option, just more parts to suck juice....

Sharing the SCSI Bus with a PC

Many of us share a hard drive between the K2K and pc; making program/sample transfers much faster and easier. Just be sure that the SCSI bus is correctly terminated! The trick here is that the ends of the cable need to be terminated. The terminations are resistors tied to the 5V line. The K2K has a terminator embedded on the synth board itself. Your pc's SCSI controller would also probably have one, and your hard drive would have one..... that's too many! If you have the drive in the pc, you normally would need the synth on to terminate the far end of the SCSI cable or you'd get errors on disk transfers. Some people switch the bus from the K2K to a cable terminator using a bus switch. I did something which I think is better. On the SCSI bus there is a line called "terminator power". This is 5V from the controller/pc side. Although the K2K sources 5V to this line on the bus, it's internal terminators are tied to the synth's internal 5V not terminator power! If you cut the line from synth 5V to the terminators and install a 1N5817 schottky diode from them to terminator power, you have the best of both worlds - with the synth off the terminator is powered by the cable power, and with the synth on/pc off the synth's terminator power feeds the pc/host side of the cable. You will have to be sure to have the pc controller supply terminator power - a jumper function sometimes. You also want the terminator removed from the controller and installed on the drive. The drive is on one end of the cable, the synth on the other. I don't believe in installing the drive in the synth as the power supply is really overtaxed and there is too much heat in the synth case due to all the load.

More on Hard Drives, ID's, and SCSI

As I stated above, the power supply is really maxed out if it has to power a hard drive in addition to the synth and it's options/memory. It gets damn hot as it is. Many hard drives will require close to a half an amp on the 5 volts. Motor starting currents on the 12 volt line can approach 2 amps or more. You also have to worry about powering the required fan. You might want to think about providing a separate external supply for the drive. Laptop battery eliminator supplies that you may be able to find surplus should do fine.

Each device on the SCSI bus has to have its own unique ID selected, usually by a jumper or switch. It doesn't matter what the ID is - as long as each is different. You can select one of 7 ID's. Your synth will tell you what is connected and each device's ID. Terminators have to be physically on the ends of the SCSI cable. If you have an internal hard drive and don't use the SCSI port in the back, the synth's terminator needs to be installed (normally is) with another on the hard drive. If you do plan to use the SCSI port you probably need to remove the terminator on the synth board, terminate the drive, and have some kind of terminator that can plug the DB25 connector when a cable is not used (with a terminator at the device/controller at the end of the cable that plugs in here). Yes, it gets messy!

In addition to termination and ID hassles, you may have additional problems with capacity, compatibility, and types of SCSI busses. SCSI drives at 750mb and below are generally compatible capacitywise. Larger than that depends on your synth's level of firmware. Contact YC to get the details - you may be able to use a larger drive but just not use ALL of it. Several drives - hard drives and CDROMs - just plain don't work due to the SCSI chipset they use. I had trouble with a CDROM with an NEC controller chip. Best post a message on the K2000 mail list to check compatibility. Finally, take a look at the connector on the back of your unit. It is called a DB25. Newer SCSI drives and controllers use a different type connector style, called SCSI II (two). This is a smaller, thinner connector style. There are adapters to interchange these and the older cables/connectors but they aren't cheap. If you are recording you may want to disconnect the SCSI cable from the synth and pc to make things quieter.

Effects Channel Op Amps

At some point in time I'd like to replace the several of the op amps used in the effects channel (TL072/4) with quieter varieties to see if it would make a difference. There are really a lot of op amps in this circuit's signal path and it could be part of the reason the direct outs sound better.



email me: barry.l.klein@wdc.com
created 5-5-99

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