SAE 2700B
Twenty slide controls per channel, a pink-noise button, and a rack ear on each side - SAE's half-octave equalizer built for the studio but just as happy in a serious listening room.
Overview
The 2700B is the rack-mount half of SAE's two-channel half-octave equalizer pair. The home-cabinet Model 27B is the other half. The 27B was dressed for the living room. The 2700B came in a rack chassis with a 600-ohm line output, aimed at professional and domestic buyers alike. The circuitry inside is the same instrument, and plenty of owners bought the rack unit for a home system simply because it was the one that showed up on the used shelf.
The core of the thing is density of control. Each channel carries twenty frequency bands, spaced a half octave apart, spanning 20 Hz to 20 kHz. Each band gets its own vertical slide potentiometer with a range of ±16 dB. A front-panel switch drops the maximum range to 8 dB for finer work. A pushbutton engages the equalizer-defeat function, so a listener can A/B the correction against the flat signal without repatching anything. DB Magazine (October 1975, p.13) noted the dual-channel design delivered +23 dBm for recording applications. That is enough output headroom to sit in a signal chain feeding tape, not just between a preamp and a power amp.
SAE built a pink-noise generator into the unit, operated from a front-panel pushbutton. It's the feature that separates a serious room-correction tool from a glorified tone control. Feed the pink noise through the system, watch a real-time analyzer (or trust your ears against a known reference), and the twenty half-octave sliders let you chase down room resonances and equipment deficiencies band by band. Modern Recording (December 1976, p.16) flagged the generator as a headline feature of the design.
The numbers SAE quoted were respectable for the period. Intermodulation distortion was rated at 0.02%, and harmonic distortion likewise came in under 0.02%. Output was specified at 11 volts RMS into a 600-ohm load. That is the professional line-level convention, and the reason the 2700B carries the "600 ohms line" designation. The noise figure was quoted as "better than 90 dB", which is a single number with no reference level or weighting, so it tells you less than it appears to.
Both sections run from built-in IC-regulated power supplies, which simplified installation in a rack full of other gear. The two channels are complete and independent. The 2700B can be used as a stereo equalizer, as two mono units on different sources, or as a single channel of very fine correction with the other side idle. Recording Engineer (October 1975, p.6) reproduced the front panel in its new-products column. It's a wall of sliders with the pink-noise button, defeat switch, and range selector clustered to one side.
Pricing at introduction was $600 for the rack-mount 2700B against $550 for the home-cabinet 27B. That's a $50 premium for the rack ears and the 600-ohm line output, per both Modern Recording (December 1976, p.16) and the product announcements of the day. In the mid-1970s that put it in serious-hobbyist and small-studio territory. A 1982 Mix studio directory lists a 2700B in the outboard rack at Cirkus Audio Group in Hollywood, alongside UREI limiters and an Eventide Harmonizer.
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