T6118A, T6118B, T6118C (1981): These are Kawai’s first custom drum ICs. 24 pins, clock is 1.6 MHz, manufactured by Toshiba. They each generate 6 channels, and the A/B/C suffix denotes different variants for different sets of sounds. They’re used in the DX series organs. The high end organs have all 3 ICs (15 sounds total), while the lower end models use only the T6118A and T6118B (10 sounds).

These are the sounds made by each IC, with the original names from the service manuals:

  • T6118A: Hihat-L, Hihat-S, Cymbal, Hi Conga, Clave, Bass D
  • T6118B: SD (Tone), Rimshot, Low Conga, Cowbell A, Cowbell B (these are used together) SD (Noise)
  • T6118C: Low Bongo, Low Tam, Guiro, Tamb., Wow-Gui. The remaining channel is unused.

They appear to continuously generate digital waveforms, which are either stored or synthesized, then sent to an onboard waveform DAC. This is externally buffered and sent back into the IC for enveloping via a second multiplying DAC. The output of this DAC is again buffered and again sent back into the IC for demultiplexing. The 6 outputs then go to sample and holds, then analog filtering and mixing circuits. The input seems to be simple trigger pulses, with no accent. So in total, each IC contains waveform generators, envelope generators, two DACs and demultiplexer control circuits.

Kawai R100, R50, R50e, R50iii (1986-87): These are 8 note polyphonic drum machines. Although they can transpose samples, there are no envelopes, so they’re not really full fledged romplers. Similar hardware is likely used in the ADEPT2 and ADD series Kawai organs.

They’re based around 3 custom gate arrays:

MB63H158: “Sensor LSI”, 64 pins, made by Fujitsu. This is a simple gate array that scans the front panel buttons and drum pads and calculates pad velocity. It’s also used as a keyboard scanner in other models, like the K1, K3 and K5.

The sample playback gate arrays are made by Mitsubishi:

M60009-0104FP: AGU “Address Generation Unit”, 100 pins. This interfaces with the CPU and contains the phase accumulators and address generation. It seems to contain all the registers for sound generation, and sends amplitude data and timing signals to the DGU IC.

M60009-0103FP: DGU “Data Generation Unit”, 100 pins. This contains the anti-log table and output accumulators, sends data to the DAC and controls the sample and holds.

The waveform ROM is 256k x 16, storing both 8 bit header data, which goes to the AGU, and 12 bit waveform data, which goes to the DGU. The data isn’t packed in any clever way, so the remaining space is wasted. The samples are recorded at 31.25 kHz (not 32 kHz as is incorrectly claimed in the user manuals). The R100, R50 and R50e each have different waveform ROMs. The rare R50iii contains an expansion board with all 3 ROMs. The AGU can only address 256k, so only one waveform ROM can be used at a time. The waveform data is stored in a logarithmic format. Like Yamaha’s FM ICs, the amplitude is scaled without a multiplier by adding the amplitude information to the logarithmic waveform data, then passing the sum through an anti-log table. This is equivalent to multiplication since, a * b = exp(log(a) + log(b)). There doesn’t appear to be an amplitude envelope, so the scaling is used only for the sound level, velocity and panning.

The master clock is 5 MHz and the playback sample rate is 31.25 kHz (160 clocks per sample, 16 clocks per voice plus 16 clocks for each stereo output channel). The DAC is 12 bit linear (DAC312 in the R100; the R50 apparently uses a cheaper resistor array). There are 8 monophonic output channels, plus stereo mix outs. The DGU IC internally pans and accumulates the sounds, and the stereo outputs get their own time slots for conversion. While this is electronically simple and more flexible than drum machines that use analog mixing to assign output channels to fixed panning positions, it also means that the stereo mix outputs have lower dynamic range (12 bits per output) than an analog mix of the individual outputs (approximately 14-15 bits depending on how the channels are panned). The sounds can be tuned chromatically over a range of -8 to +7 semitones, but the flange effects in the R50 adjust the pitch more finely, and it’s not unlikely that the hardware supports a larger transposition range. Interpolation seems to be truncation. Coupled with the low playback sample rate, this results in a dirty sound similar to the E-mu SP-1200 or Ensoniq Mirage.