Marantz Model 2440 (1972)
The Model 2440 was not a receiver, not an amplifier in the usual sense, and not a tuner. It was Marantz's "Quadradial Adaptor-Amplifier," a box designed to bolt four-channel capability onto an existing two-channel stereo system. The service manual calls it a "Solid-State Quadradial Adaptor-Amplifier," and that awkward name tells you what it was. It decoded and adapted four-channel sources, and it had its own power amplifier to drive the added rear channels.
Marantz's advertising from the period pitched it at the reluctant upgrader. High Fidelity (January 1973, p.17) ran copy aimed at listeners who "got the urge to go 4-channel, but don't want to give up your great stereo system." The 2440 was the way to keep the stereo you already owned while adding full four-channel. The same ad copy, which also appeared in Audio (March 1973, p.96), rated the unit at 40 watts continuous RMS. Marantz also claimed a snap-in, snap-out decoder scheme that would let the owner accept optional SQ matrix decoders and CD-4 demodulators as those formats developed. That was a hedge against the format war, since nobody in 1972 could say which four-channel system would win.
The service manual shows what's actually inside. The chassis is built from discrete functional blocks, each on its own printed circuit board:
- Front Channel Buffer Amplifier — P.C. Board P100
- Tone Control Unit — P.C. Board P200
- Balance Control Unit — P.C. Board P300
- Tone Amplifier — P.C. Board P400
- Vari-Matrix Unit — P.C. Board P500
- Meter Amplifier — P.C. Board P600
- Power Amplifier — P.C. Board P700
- Power Supply — P.C. Board P800
The mode switch (S004) had MONO, 2 CH, DISCRETE, VARI-MATRIX, and SQ DECODER positions. In VARI-MATRIX, two-channel stereo was synthesized into four channels, with the rear-channel content governed by a DIMENSION control. At minimum the rear channels collapsed toward mono, at center they were stereo, and at maximum they went out of phase to throw the image outward. The SQ DECODER position required the separate Marantz SQA-1 SQ adaptor to be plugged in. The 2440 did not decode SQ on its own. Balance was handled by three separate balancers (front L-R, rear L-R, and front-rear). A REMOTE switch made the optional RC-4 Remote Control Box operative. At that point the 2440's own balancers were bypassed and the RC-4 took over level and balance duties, though the RC-4's maximum volume was still capped by the 2440's master volume control.
Servicing notes call for an 8-ohm load (with a 0.5 mfd capacitor switched off) and a 1 kHz test signal at the 5V range for output power measurement. The manual is explicit that the 2440 is aimed at "the knowledgeable and experienced technician only."
Beyond the service manual and the 1972-73 ad campaign, the record on this model is thin. It was a transitional, format-hedging product from the peak of the quadraphonic era, and like most such adaptors it has been largely forgotten as the four-channel formats faded. Surviving units turn up occasionally. Documentation is limited to the service manual and period advertising, with no independent lab reviews.
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