Portable Electronic Organ
Made in 1981 by Kawai Musical Instruments of Japan, the KMA-37 is a strange little keyboard. With only three buttons to control its sound (excluding the rhythm functions), it has the most basic tonal capabilities of any electronic organ I've ever seen. Its width of 37 keys is narrower than a normal combo organ keyboard (usually 49 or 61 keys), as well as typical spinet organ manuals (usually 44 keys). Pitch-wise, its range of C4 to C7 is quite high. It also has a built-in analog drum machine, with extremely basic presets consisting of a bass drum on the first beat, and a snare-like drum on every subsequent beat. "Metronome" eliminates the bass drum.
This is a very uncommon instrument, despite being manufactured by Kawai, which was and still is a leading keyboard manufacturer. I have found only one reference to it aside from those I have made myself, which is that one was repaired in 1990; see here. Kawai's websites do not have any info, so in July of 2014, I contacted Kawai US, asking if they had any kind of information on the unit. The answer was no—neither the fellow I conversed with nor his Japanese colleagues had anything. No new info has been sent to me by readers since the first version of this article was published in late 2014. I've also found nothing on any other KMA series instruments; if they exist, they would probably be similar except with different numbers of keys, considering this KMA-37 has 37 keys.
What would be the intended market of this instrument? The functionality is most comparable to toy instruments. Yet, the build quality indicates that it is no toy—from the full-size keys with a great feel, to the sturdy metal and wood cabinet, it displays a quality that even at the time was becoming rare, and which is now especially rare. Yet of course, the limited pitch and tonal ranges make it unsuitable as a professional instrument. My best guess is that it was intended as a kind of portable practice organ for music students.
To give some background, I found this keyboard at a thrift store in Lacombe, Alberta for $10.00 in August 2013—it had just come in, and upon seeing it, I knew it was something of interest. I have not had to perform any "real" repairs; I simply cleaned the pots with Electrosolve, and applied a bit of glue to stabilize a crack in one wood block, but that's trivial stuff. I also figured out where the tuning control was, and adjusted it (see the Hardware section). In any case, I publish this article to serve as the only source of info on this unit. If you own a KMA-37, please contact me, since I would like to know if any more of these still exist.
The build quality is relatively high. The casing is made of metal and wood; mostly plywood with faux-wood veneer, some faux-wood-veneered particle board, and some solid hardwood mounting blocks. The metal top cover is held by 12 screws, to give enough strength for the instrument to be carried by a handle mounted to the cover. On the back can also be seen the builder's plate, the two outputs, and two rectangular holes, which are probably for mounting a long-gone music stand. The "EXT. OUT" does not interrupt the internal speaker, while the "HEADPHONE" output does. As expected, the "HEADPHONE" output makes a nice high-level output for recording and external amplification, but take care to use stereo connectors so as not to short out the right channel.
There is another peculiar feature on the back. Have you spotted it? Check out the heavy-duty chrome-plated TEISCO end caps on the handle! Teisco was a Japanese company that made guitars, amps, and combo organs in the 1960s especially. Kawai bought Teisco in 1967, and discontinued the brand in 1969 except for electronic keyboards, which continued "until the 1980s" according to Wikipedia, so this explains the connection company-wise. I then tried to find a connection on the instrument level, researching Teisco keyboards of the same era, but I only found synthesizers with little resemblance. The Teisco Synthesizer 110F uses two of the same knobs, and the font is the same—this is the strongest connection I've found to Teisco instruments. There is also a connection to Kawai home organs of the same era (such as the DX900), some of which use the same buttons, and the same lettering font.
Below shows the bottom of the instrument. Towards the front, there are two brown plastic pieces spaced the same horizontally as the rectangular holes in the back. I suspect these pieces, along with the metal bracket in the middle, were designed to hold a metal wire music stand to the bottom when not in use. I imagine something similar to the stands on Hewlett Packard test gear such as the 651B; you can look it up to see what I mean. However, I cannot imagine a plain metal wire stand mounting properly to the rectangular holes in the back, so it is still not certain what kind of design was used.
Removing the twelve screws and carefully moving the metal panel out of the way reveals the insides:
The electronics are typical for 1981. As many functions as possible are implemented with ICs: the voltage regulation, tone generation, power amplification, and so on. Unfortunately, this makes this instrument less easily repairable than earlier organs made with discrete parts, since some of the ICs are long out of production and increasingly scarce, whereas discrete parts are still in production, and common. Especially the TMS3615-25NS tone generators are scarce, and would be difficult to substitute since there is no datasheet online (until now; see addendum at bottom). In fact, I can only find TMS3615NS for sale in the proper shrink-dip package, and I don't know the difference between it and the -25NS; my guess is that it would probably work, but I can't say for sure. The TMS3615NL in a normal DIP package was widely used, especially by Italian companies such as Crumar, Farfisa, GEM, Siel, and so on... see here.
Near the left end of the left tone generator board (seen in the upper right corner of the above image), you can see a variable inductor. This is the master tuning adjustment—rotating its core tunes all notes on the keyboard. Use a plastic screwdriver, and be very careful so as not to crack the ferrite core.
The small oval-shaped internal speaker can produce a moderately loud output, driven by a Sanyo LA4230 6-8W amplifier chip. Neither of the volume controls can actually be turned all the way down; a small amount of signal comes through at minimum setting. The internal wiring harnesses are neatly arranged and laced with clear plastic cord (very common in this era of Japanese equipment), and most connections between boards are made with 0.1" Molex connectors, which would make removing and replacing boards quite easy.
Again, there are still many confusing aspects of the unit. It is basically a 37-key electronic organ with very limited tone settings and rhythms, with excellent build quality; quite an odd combination of features, really. What was the original intended purpose of this keyboard? It's too limited in tone and range for most professionals to perform with. Perhaps it was made as a practicing unit, but if so, why such a high-pitched range (C4 to C7), and why such high build quality? These questions may never be answered, to the disappointment of millions...
A reader in Ukraine known as T-150 (named after the Soviet tractor) has kindly sent me the datasheet for the TMS3615-NS tone generator chip, which I have uploaded here—I believe this will be its first time online. As can be seen, this chip takes one high-frequency clock as input, and divides this frequency by certain factors (listed on page 8) to give 13 square-wave pitches spanning one octave, spaced in semitones—these pitches comprise the 8' footage. The 8' pitches are each divided by 2 (i.e. lowered an octave) to create the pitches comprising the 16' footage. Each pitch is fed to its own "analog modulator" (i.e. variable-gain amplifier), which modulates the amplitude based on the "sustain bias" voltage, as well as the voltages on the 13 key inputs. The outputs of the 8' modulators are summed to a single 8' output, and similarly for the 16'. This leaves little to do outside of the chips—just basic filtering and effects.
You may wonder why the chip produces 13 notes instead of 12. This is so that the keyboard's range can start and end on the same note. Have a look; how many C keys are there? Four, yet there are only 3 tone generator chips. Either the lowest- or highest-octave chip is responsible for two C keys (I don't know which, since I still have no schematic, nor have reverse-engineered it, nor does it really matter!) If the chips only gave 12 notes, the instrument would probably have started on C and ended on B.
Note as well that the "sustain" features of the chip are not really used by the KMA-37. The manual states that sustain of the notes is possible by adding a 1µF capacitor to each key input, and that the sustain time is adjustable ("from a few ms to a very long time") by adjusting the voltage on pin 4 ("SUSTAIN BIAS"). My preservationist nature prevents me from modifying this instrument to try it out—it is enough for me to know that it is possible. I should note, however, that already there is a short yet noticeable "sustain" time, and a short "attack" time.
The "flute" tone is mellow and comprised of roughly triangular waves. The "organ" tone is brighter and closer to a sawtooth/ramp in shape. Having both tone buttons pressed in at once combines the two additively. As mentioned above, there is a very short "attack" time at the beginning of a keypress, and a similarly short "sustain" time at the end. The vibrato is very basic, with a medium frequency, and a low amount of "depth". It's easy to forget that you've turned on the vibrato once it's been on for a while, since it is so subtle.
After observing the output waveforms on an oscilloscope, it appears that the "flute" tone results from lowpass-filtering of the 16' squarewave outputs from the tone generator chips, and the "organ" tone appears to be from lowpass-filtering of the summed 16' and 8' squarewave signals. See the images below:
Note how the waveforms become both smoother and lower in overall amplitude with increasing pitch, undoubtedly as the fundamental frequencies approach (and pass) the filter cutoff frequencies, resulting in greater attenuation of especially the low-order harmonics relative to the fundamental, but also the fundamental itself. Note how the "flute" voice begins a rounded square at C4, becoming a fairly good triangle wave by C7. The "organ" voice also begins close to the summation of 16' and 8' squares of equal amplitude, yet also approaches a triangular shape. Anyway, I cannot say more without doing some proper circuit-tracing, but I figure this is an interesting addition nonetheless.
The "Rhythmer" is a neat little rhythm unit, also very simplistic. There are 5 on/off buttons for selecting the rhythm pattern: metronome, 2/4, 3/4, 4/4, and 6/8. Buttons to the left override buttons to the right, however the 6/8 button doubles the speed of all rhythms no matter what. Each beat consists of a burst of noise controlled by a simple volume envelope (sounding similar to a snare drum), with the downbeat also including a "blip" of low frequency content, giving a sound like a bass drum. The simple snare and bass drum combination calls a marching band to mind.
As with most organs, the KMA-37 makes a great lead instrument when used with some overdrive/distortion. One example of this can be found on my 2014 album Demos, or perhaps not..., on the track "Sixties Five", where I use it with a wah pedal and a homemade "Valve Caster" tube overdrive, which has fairly low gain and gives a dark, crunchy sound. It also makes an appearance on my album Ридахций at the 22:26 mark, where the rhythmer is used to produce a repeating pattern of 11, 10, 9, ..., 3, 2, 1 beats, by means of quickly activating and deactivating the 2/4 button. Neither of these are especially great performances—my ability and tastes have improved since then, though the albums still have worthwhile moments. Maybe at some point I will make a proper demo, but it is low on the priorities, unless it is requested.
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