Nakamichi CA-50II (c. 1987)

The CA-50II is Nakamichi's Japanese-domestic control amplifier. It is the 100V version of the second-generation CA-5 series preamp, sold alongside the multi-voltage CA-5II, the 120V CA-5AII, and the 220V CA-5EII. The variants are the same amplifier with different power-supply regions, and a forum reading of the service manual holds that they don't differ internally otherwise. It listed at ¥210,000 around 1987, with a later Japanese-database figure of ¥200,000 around 1989. Nakamichi described it as an improved CA-50 carrying technology from the flagship CA-70.

The phono stage is the centerpiece. The MC head amp uses a parallel push-pull input built around super Hi-gm FETs to keep noise down, with gain selectable at 36, 30, or 24 dB. MC load resistance is fixed at 100Ω from the factory, but a service center or dealer can swap it to 50, 30, 20, 10, or 3Ω. MM load capacitance switches among 100, 200, and 300 pF. The equalizer and line stages run a two-stage differential topology, with a dual-FET differential input first and a bipolar differential second. They feed a final buffer that's an emitter follower with current bootstrap, held in full Class A. RIAA deviation is quoted at ±0.25 dB (MM) and ±0.3 dB (MC) across 20 Hz - 20 kHz, with phono THD of 0.001% (MM) and 0.004% (MC at 36 dB). Line response reaches 1 Hz - 100 kHz +0/−3 dB, and S/N is 95 dB or better on line inputs, 88 dB MM, 81 dB MC.

The build is unusually fussy for the money. The audio circuit is laid out L/R twin-mono, the front and bottom chassis are copper-plated, and the aluminum chassis is stiffened for vibration resistance. The supply is multi-regulated in two constant-voltage steps and fed by a toroidal transformer. An isolated ground system uses an FET buffer in the supply line to kill ground interference. Signal wiring is oxygen-free copper on an oxygen-free-copper-patterned epoxy board, input switching uses crossbar twin relays wired straight to the terminals, and the jacks are gold-plated. The power cord is notably thick and polarity-marked. A remote power on/off terminal (24V DC) lets the unit link with compatible Nakamichi gear via the separately sold SPC-1J system control unit (¥25,000), and a tape mutual-dubbing function is included. It measures 435 × 63 × 287 mm and weighs about 5.1 kg.

Reception is thin. No period audiophile reviews have surfaced, and the detailed specs trace largely to a single Japanese database. What survives is mostly owner and seller material. One Russian listing praises the "superb MM-MC phono preamp with settings for a specific cartridge," and units turn up on Yahoo Auctions Japan and Avito, often paired with the matching PA-50 power amplifier (the two together originally listed at ¥460,000). Service manuals are readily available: 28 pages, English, with circuit diagrams and a parts catalog. Buyers outside Japan should note the 100V input.

Known specifications:

• Phono MC: 45 µV/100Ω (36 dB gain); selectable 30/24 dB
• Phono MM: 2.5 mV/50kΩ; load capacitance 100/200/300 pF
• Line inputs (Tuner/CD/Aux/Tape): 150 mV/12.5kΩ
• Pre-out: 2V/1kΩ; Rec out: 150mV/1kΩ
• S/N: 95 dB (line), 88 dB (MM), 81 dB (MC, 36 dB)
• Tone: ±10 dB at 20 Hz (bass) and 20 kHz (treble)
• Power: 100 VAC, 50/60 Hz; consumption up to 23W
• Dimensions: 435 × 63 × 287 mm; 5.1 kg

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