Lexicon PCM 70 (1985)

The PCM 70 was Lexicon's mid-1980s entry into rackmount digital effects. The manual tells you more than any marketing sheet does. It's a single-rack-space unit, 19" wide, 1.75" high, 13.5" deep, made for a standard 19-inch rack or any level surface. Around back are unbalanced left/right outputs on 1/4" tip/sleeve phone plugs. Output impedance is 600 ohms regardless of the level setting. Output level is set by a front-panel pushbutton and also varies with the program running. The manual is emphatic on one point. If you patch the PCM 70 into a console via an effects loop or aux send, set the MIX parameter (0.0) to 100% wet, or turning up the send and return just makes the dry signal louder. Plug an instrument in directly instead, and somewhere between 45 and 65% is a reasonable place to start.

Under the hood it's a computer-based device, and the manual is unusually candid about that. Lexicon built in protection against power-line noise, spikes, and hash, but the memory can still get scrambled. The documented fix is a power-cycle, then pressing the 8 key when the software version appears. That prompts "CLR ALL BUT REGS" and clears memory without wiping user registers. If that doesn't work, the full reset erases all registers but leaves the factory presets intact. Press 0 at the version prompt, then confirm at "CLEAR MEMORY?" and "ARE YOU SURE?" A lithium battery maintains data memory, meaning parameter settings and user registers, with a service life of up to five years. When it's nearly spent, "BATTERY LOW" appears at power-on, and Lexicon or a dealer should be contacted for replacement. Register protection is a separate feature that can block overwrites if it's switched on.

The manual that accompanies Software Version 3.00 is copyright 1985 and 1987, and the Rev 1.1 printing is dated 03/87. So the PCM 70 had a real software revision history, with the 3.00 release adding features over earlier versions. The preset programs are organized into rows: Row 0 echo and chorus, Row 1 multiband delay, Row 2 resonant chord, Row 3 concert hall, Row 4 rich chamber, Row 5 rich plate, Row 6 inverse room. Parameters are grouped into effects, reverb, and control categories, and not every program exposes all of them. The MIDI implementation is deeper than you'd expect for the era. Each program carries ten patches. These let performance events (last note played, aftertouch, velocity) or controls like volume, pitch bend, mod wheel, and footpedal drive up to ten different parameters in real time. You can link two PCM 70s together, move registers between them, control one from a keyboard or sequencer, and store or edit registers from a microcomputer.

Contemporary advertising leaned hard on that dynamic MIDI angle. Studio Sound (May 1986, p.65) ran Lexicon's copy describing the PCM 70 as an "extraordinary new digital effects processor with dynamic MIDI," pitched as a way to vary any parameter from a MIDI keyboard while playing. The same advertisement appeared in Studio Sound in January, April, and June 1986 and in Mix in September 1986. That's a lot of trade press space for one box in one year. A decade on, Sound on Sound (August 1996, p.197) still called the PCM 70 "legendary" while introducing the PCM 80, and noted that the newer unit's algorithms were based on both the PCM 70 and the 224.

The record is thin in a few places. There's no original list price in the material on hand, no production-run figures, and no design-team credits. The manual is thorough on operation and thin on history. If you're trying to date a specific unit, the software version shown at power-on is your best clue. 3.00 is the revision documented here, and earlier units would have shipped with earlier firmware.

• Digital effects processor, one rack space (19" × 1.75" × 13.5" / 483 × 45 × 344 mm)
• Unbalanced 1/4" TS left/right outputs, 600 ohm output impedance
• Lithium backup battery, up to five-year service life; "BATTERY LOW" warning at power-on
• Documented with Software Version 3.00; manual copyright 1985, 1987; Rev 1.1 dated 03/87
• Preset program rows: echo/chorus, multiband delay, resonant chord, concert hall, rich chamber, rich plate, inverse room
• Dynamic MIDI: ten patches per program, real-time parameter control from keyboards, sequencers, and controllers
• Two PCM 70s can be linked; registers movable between units; microcomputer register editing supported
• Maximum ambient operating temperature 35°C (95°F)

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