Marantz 1200B

A stereo console amplifier rated at 100 watts per channel into 8 ohms, and 125 into 4. Marantz's own service documentation is written in the careful, unhurried language of a company that expected these to be repaired, not replaced.

Overview

The model number on the front panel and the model number in the service literature don't quite agree. Know that before you go looking for one. The factory documentation is titled for the Marantz Model 1200 Stereo Console Amplifier - a service manual issued to authorized warranty stations, describing a unit built by The Marantz Company, then a subsidiary of Superscope Incorporated, in Sun Valley, California. The pages inside that same manual carry the heading "MODEL 1200B" on the board diagrams. Collectors chasing parts and schematics should search both designations. The two are the same machine.

The manual spells out a power amplifier with honest, load-dependent ratings. Both channels driven, 20 Hz to 20 kHz, the 1200B is rated at 100 watts per channel into 8 ohms, 125 watts into 4 ohms, and 50 watts into 16 ohms. The 4-ohm figure is the interesting one. Plenty of amplifiers of the period quoted a single 8-ohm number and quietly fell apart into low-impedance loads. Total harmonic distortion, measured including the preamplifier section, is specified at less than 0.15 percent at or below rated power across the full 20 Hz to 20 kHz band. Intermodulation distortion gets the same treatment: less than 0.15 percent by SMPTE method, any combination of two frequencies, again 20 Hz to 20 kHz, again including the preamp. Those aren't spectacular numbers by the standards of the spec-sheet arms race, and Marantz clearly wasn't playing that game.

Frequency response is quoted as +0/−3 dB from 6 Hz to 80 kHz, with a tighter ±0.25 dB window from 20 Hz to 20 kHz. A 6 Hz bottom end is the kind of figure that shows up when the output transformers and power supply have been over-built rather than trimmed to a price. The phono input is specified at 1.35 mV sensitivity into 47 kOhms. That is a fairly typical moving-magnet loading, and a healthy MM cartridge will drive it without strain.

The preamp section is where the 1200B shows its ambitions. The service manual's circuit description walks through a low-level amplifier built around a single-ended differential pair, an inverter stage, and an emitter follower, providing 40 dB of gain. Three low-level inputs and three high-level inputs feed a selector switch that also chooses the equalization network - flat or RIAA - for the phono stage. Tone controls are switch-defeatable, with bass specified at ±10 dB at 100 Hz. The filters are ganged across both channels: a high filter, and a low filter switchable between 50 Hz and 100 Hz.

The test procedures in the manual show how tightly Marantz expected these to hold tolerance in the field. The low filter, engaged at 50 Hz, should produce a drop of −3 ±1.5 dB. The same goes at 100 Hz. The high filter, at 5 kHz and again at 9 kHz, should land at −3 ±1.5 dB. Bass and treble controls at full rotation should give +10 ±2 dB and −10 ±2 dB. The loudness contour, referenced to 1 kHz, should produce −7 ±2 dB. Channel balance at mechanical center should hold within 0 ±2 dB. These are the tolerances a warranty station was expected to hit on a customer's unit, not lab-grade best-case figures. They're generous enough that a 1200B in decent health should still meet them today.

The specs tell most of the story here. A 100-watt-per-channel amplifier that delivers 125 into 4 ohms, holds distortion under 0.15 percent across the audio band including the preamp, and passes signal from 6 Hz to 80 kHz is not a colored, romantic piece of gear. It's a clean, quiet, high-headroom amplifier with a competent phono stage and a flexible control section. The tone controls and filters are defeatable. With them out of the circuit, the 1200B is a straight wire with gain. With them in, it's a period-correct console amplifier that can tame a bright cartridge or a boomy room.

The service documentation is unusually complete for a unit of this vintage, which is a real practical advantage. The manual includes a full parts list with Marantz part numbers for resistors, capacitors, switches, transformers, and even the plastic feet. It also has a list of illustrations covering every board in the amplifier, from the interconnect board through the phono amplifier, X10 amplifier, tone amplifier, power amplifier, power supply, and rectifier/relay boards. A test equipment list names the specific instruments a warranty station was expected to use, including the Hewlett-Packard 331A or 333A distortion analyzer, a Weston CVO-100P audio oscillator, a Tektronix 503 oscilloscope, and a Simpson 390 AC wattmeter. A competent technician can still service a 1200B today, which makes it a reasonable candidate for restoration rather than a shelf piece.

Go in with realistic expectations. The 1200B is not one of the Marantz receivers that commands silly money on the used market, and the thin period review coverage means it doesn't have the reputation-driven pricing that follows a well-reviewed flagship. What it has is solid engineering, a useful feature set, and the build quality of a company that issued a service manual to warranty stations rather than treating the product as disposable. Expect to find units with tired electrolytics, dirty selector and filter switches, and possibly a failed relay. All of that is documented in the manual and repairable. The toroid in the power supply and the output stage components are the parts to inspect carefully on any example, since replacements are not off-the-shelf.

For a period system built around a turntable and a pair of efficient speakers, the 1200B is a sensible, unfussy choice. It has the inputs you need, the phono stage is properly implemented with switchable RIAA equalization, and the power is honest. It won't flatter a bad recording, and it won't add warmth that isn't there.