Nakamichi CA-5AII
A phono-first preamplifier that let dealers fine-tune your cartridge loading with a bag of resistors - and warned you not to open the case yourself.
Overview
The CA-5AII is a Nakamichi stereo preamplifier. It belongs to a small family of near-identical variants that the company distributed by territory: the CA-5II, the CA-5EII for Europe, the CA-50II for Japan, and the CA-5AII for the United States and Canada. The differences are mostly packaging and paperwork. The service documentation lists distinct carton boxes, front-panel assemblies, chassis assemblies, and owner's manuals for each market, including English, German, French, and Japanese editions. A collector chasing a CA-5AII specifically wants the North American version, and the part numbers confirm it: the U.S.A. and Canada chassis and front-panel assemblies carry their own designations.
The interesting part for anyone who actually plays records is the moving-coil phono stage. The load impedance for an MC cartridge is factory-set to 100 ohms. Nakamichi shipped the unit with a supplement of resistors, five each for the left and right channels, that a dealer could install on the printed circuit boards to change that loading. The documentation is blunt about who should do the work. It is a dealer-only modification, and the manual warns that opening the unit carries a considerable risk of electric shock.
The circuit is a discrete, low-feedback design. According to HiFI-Stereo (April 1988, p.45), the CA-5AII was designed for negligible distortion without overall feedback, and it needed only a moderate amount of feedback to meet its performance specifications. The same report, credited to Julian Hirsch of Hirsch-Houck Laboratories, describes the measured performance as exceptional. Hirsch's lab reports were known for being unsentimental.
The parts list reads like a proper audiophile preamp of its day: µPC811C integrated circuits in the line amp, 2SA970 and 2SC2240 transistors, a 2SK240 FET, and a pair of DS2Y-S-DC24V relays. The power supply is fused at 1.6A 250V for the main rails, with a separate T800mA fuse specified for the Australian, Saudi Arabian, and European variants. There's also a spark killer on the power switch: an XE-473 for the CA-5II and CA-5EII, an ECQ-JC187C for the CA-5AII specifically, and an AU 120033 for the CA-50II.
The front panel carries a power button with its own guide and lens, a volume knob on a dedicated holder, and a function switch with its own nut and washer hardware. The tone switching lives on a separate PCB assembly. The layout is conventional. The service documentation treats every knob and button as a replaceable assembly, so individual parts can be sourced or substituted without a complete front-panel rebuild.
For a preamplifier of this caliber, the CA-5AII is also notable for what it doesn't do. There's no digital section, no remote, no video switching. It's a line stage and a phono stage, and the phono stage is the point. The MC loading resistors, the low-feedback topology, and the care taken with the power supply all point in the same direction: this was built for people who cared about the first gain stage in the chain.
The CA-5AII is one of several closely related models, and parts are not always interchangeable across the family. The chassis, front panel, and even the power switch PCB carry different part numbers depending on whether you have a CA-5II, CA-5AII, CA-5EII, or CA-50II. If you're buying one to restore, verify which variant you're getting before you order parts. The documentation also includes a production date seal for the CA-5AII, which is useful for dating a unit.
The CA-5AII is a serious phono preamp from a company better known for cassette decks. It doesn't have the cult following of a Dragon or a 1000ZXL, and that's probably why prices have stayed reasonable.
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