Kawai K4R

A rackmount K4 with the keys stripped away. Same engine, less furniture, and a service manual that tells you exactly what's inside.

Overview

The K4R is the rack version of Kawai's K4 synthesizer. The best thing about owning one today is the documentation that survived. The service manual is unusually complete. It lists the PCB set, the semiconductor complement, the individual chips, and the mechanical parts. So a K4R that misbehaves can be diagnosed instead of guessed at. Collectors who work on their own gear tend to value that more than any spec sheet.

The architecture shows in the board layout. The main board, the MI-056, carries the MPU, card buffer, reset, RAM, code ROM, address decoder, DCO, DCA, wave ROM, DCF, pan pot, MIDI, audio, D/A, and power supply, according to the manual. That is essentially the whole voice path on one board. The DCO/DCA/DCF trio is the digital-oscillator, amplifier, and filter chain. The dedicated wave ROM confirms this is a sample-based instrument, not an analog one. The MI-057 handles panel switches, the MI-059 handles data entry, and the MI-058 is the volume board. A rack unit's control surface is minimal, and the board set reflects that.

The chip list reads like a snapshot of early-'90s digital synth design. The tone generator is the K002FP, a 100-pin custom device, and the K4R carries two of them. A K004FP handles pan pot. The K005FP is the key scanner on the keyboard version, and the K4R's parts list leaves it out, as you'd expect for a rack. The K007FP effector and the TC51832SP PSRAM appear on the K4 board but are struck from the K4R column. That tells you the rack version's effects and sample RAM situation differs from the keyboard model. The CPU is a PD78310G-36, backed by an HM62256LP-15SL 8 × 32Kbits SRAM and a CR2032 lithium battery for patch retention. A TLP513 photocoupler and a MIDI connector round out the I/O. The audio path uses TA75558P, NJM-4556D, and TA7508P op-amps.

Power comes from an external PS-121 adapter. The manual lists market-specific variants: the PS-121 D for Japan, PS-121 U for the U.S.A. and 110V markets, PS-121 N for 200V markets, PS-121 S for Australia, PS-121 G for the U.K. and 220/240V markets, and PS-121 W for West Germany. Fusing differs by region too - a TSC 1A 250V for Japan, an MT4 1A 250V for the U.S.A. and Canada, and a SET 1A for Europe. Anyone buying a K4R without its original adapter should check the fuse rating before substituting a supply.

The display is a DMC16205-NY-LY1 LCD, and the parts list includes an LCD cover. Both are small consumables that are frequently missing on used units. The rack ears are listed as a rack adapter, two pieces, all markets. The front panel is a single part number, and the volume knob and a black knob are listed separately. That level of detail makes restoration possible.

The manual does not say how the K4R sounds, how many voices it has, what its filter is, or what it cost. Those facts aren't in the documentation at hand, so this page can describe the hardware and not the music. The K4R shares its engine with the K4. The K4 appears in period ROM-card advertising alongside the Roland D-50/D-550, Korg M1/M1R, Yamaha SY55/SY77, and Ensoniq VFX. Mix (1990, p.132) listed the K4 in a ROM-card price table, which places it in the same market tier as those instruments without settling any spec question.

The K4R is a rack unit, so it fits a studio without demanding keyboard space. The service documentation means a dead voice or a failed battery is a fixable problem. The CR2032 is the obvious first item to check on any used unit, and the LCD is the second.