Lexicon 224X (1982–1985)

A digital reverb that came with a 50-foot cable, and the cable was part of the design.

Overview

The Lexicon 224X is a digital reverb in two pieces: a 19-inch rack mainframe that does the processing, and a separate remote console that does the talking. The console is the LARC, the Lexicon Alphanumeric Remote Console. The mainframe takes up 7 inches of rack height and 15 inches of depth, weighs 34 pounds, and pulls up to 150 W from the mains. The LARC is a small desktop slab, 5.9 by 9.5 by 3.2 inches, weighing 1.9 pounds. It connects to the mainframe over a flexible 50-foot cable with DE-9 connectors, and it is normally powered through that cable. For runs beyond 100 feet, Lexicon specified an optional remote supply - 10 to 20 Vdc or 10 to 20 Vac at 6.25 W - feeding a miniature jack on the console. The reverb sits in the machine room and the engineer sits at the desk, so the cable earns its keep.

The LARC makes the machine readable. Studio Sound (October 1983, p.97) described the console as showing at a glance which family of programs is active, which specific program is selected, and which variation within that program is running. All of it is spelled out on LED displays instead of squeezed into a two-digit window. The same coverage noted that setups could be stored to audio cassette, which is how this generation of Lexicon gear handled user memory.

The 224X is derived from the standard Model 224. Studio Sound (February 1982, p.28) reported that the X combined everything the 224 did with additional facilities, and that it was introduced alongside the Super Prime Time at that year's AES New York show. This matters if you service one, because the manual is blunt: boards must not be exchanged between 224, 224X, and 224XL units. They are related machines, not interchangeable ones.

The rear panel is built for serious patching. Inputs are two channels on 3-pin male XLRs, balanced and transformer-isolated, pin 2 high, with a 20-kilohm input impedance. Outputs are four channels - A, B, C, and D - on 3-pin female XLRs, also balanced and transformer-isolated, with a 90-ohm output impedance. The 224X accepts input levels from +8 to +18 dBm, and output levels run from slightly below +8 dBm to slightly above +18 dBm. Input and output trims are screwdriver pots reached through access holes on the mainframe's front panel, not knobs on the face. Unity gain is the factory setting, with a maximum output level of +12 dBm.

Setting those levels is a procedure. The manual sends owners into the delay-line diagnostic programs, Zero Delay or 0.5-second Delay, reached by pressing PAGE and PROG together, then REG, then numeric key 7 or 8. Feed in a musical source or a 1-kHz tone at the hottest peak level the system will see, and trim until the peak sits just short of lighting the +12 dB LEDs on the LARC's upper display. The manual warns that the 224X clips abruptly, like other digital audio equipment of its era. It also says that after a RESET you should not touch the numeric-select keys until the unit resumes normal operation, because doing so can erase the user memory registers. For output levels, the delay-line program passes the left input to outputs A and D and the right input to outputs C and B. The manual is explicit that this program is for *setting* levels, not checking them, because levels differ significantly across other programs. Checking is done with program material or noise, never a pure tone.

The patching advice in the manual reads like a working engineer wrote it. The 224X is designed to sit on a mixing console in a stereo-in, stereo-out configuration, but Lexicon recommended independent sends switchable pre- or post-fader and pannable returns. The manual also notes that regular console inputs are more desirable than echo returns on a unit this versatile. Equalizing the return, about +3 dB below 200 Hz, adds richness and naturalness to reverb, while a high-frequency boost brings brilliance to drums. Phase gets its own warning: reversing polarity on any input or output produces audible phase-inversion effects, and improper phasing in the stereo echo path makes a mix weak or thin. The Chamber program doubles as a phase test, since it digitally averages the two inputs. Miswire the phases and you will hear practically nothing.

The programming is deeper than the typical reverb of the era. Controls include LF Decay, Mid Decay, Treble Decay, and Crossover, and the manual gives concrete recipes. A convincing concert hall in the Concert Hall program comes from LF Decay between 2.5 and 3.0 seconds, Mid Decay between 1.8 and 2.5 seconds, and Crossover between 600 and 800 Hz. Set LF Decay to 1 second, Mid Decay anywhere from 1.5 to 3.0 seconds, and Crossover to 1000 Hz, and you get the thin, bodyless sound of a modern hall with light-panelled, thinly constructed walls. Treble Decay, per the manual, should always sit between 6 and 10 kHz to mimic air absorption, with 6 kHz the most natural setting for those examples.

Then there is Dynamic Decay, which is where the 224X separates itself from a reverb that only knows how to start. LF and Mid Stop Decay controls, activated by the Dynamic Decay toggle, apply only to the tail of a sound — after the input has stopped. That is a different idea of what reverb is: not a fixed space the signal passes through, but a space that changes character as the note dies. For multitrack work, the Split programs let two entirely distinct sounds run on different tracks simultaneously without re-recording, and the manual notes it is not uncommon to build a different ambience for each instrument or vocal section to give each its own color.

Storage and automation reflect the period. The cassette interface runs 600-baud FSK with Hamming error detection and correction over a DIN-5 180° connector, and it can store any or all of the nonvolatile register banks. Automation was an option, not a standard feature: an RS-232C serial interface on a DB-25. RFI shielding covers the AC connector, audio connectors, and console cable, and the unit complies with FCC limits for a Class A computing device. Protection covers a lot: mains fused, secondaries fused, voltage crowbar and/or current limiting, thermal protection. The power supply is convection-cooled while the logic cards get forced air, so that is where the heat lives.

Voltage is switch-selectable across 100, 120, 220, and 240 Vac at 50 to 60 Hz, within −10% and +5%, via two changeover switches behind the front panel. That is a technician's job, per the manual, along with fitting the correct rear mains fuse: 3AG 3A slow-blow for 100 and 120 Vac, 3AG 1.5A slow-blow for 220 and 240. Units factory-set for 220 or 240 ship with 20-mm fuse adapters. Internally, the supply rails are +5 Vdc at 10 A, −5 Vdc at 250 mA, +12 Vdc at 1.25 A, −12 Vdc at 150 mA, and ±15 Vdc at 750 mA each, plus a 10 Vac transition supply at 500 mA and an internal +5 Vdc LARC rail at 1 A. Every major assembly is removable, and diagnostic programs run automatically at power-up or reset, controlled and displayed through the LARC.

A used 224X comes with a set of known faults, and the manual documents them. A pop when changing programs or using the Mute switch traces to U7 and U8, the LF353 dual opamps on the AOUT board. The fix is replacement for low bias current. Unpredictable LARC operation can come from a four-position switch on the NVS board. All switches should be open, and a few units shipped with them closed. A LARC that fails on cable runs of 1000 feet or more may have a 10-kilohm resistor at R4 on the transition board where a 1-kilohm part belongs. Software version 8.2 carries three documented bugs: no B output on the Dark Hall program, A and C outputs on Rich Split muting when Mid Decay is set to infinite, and variation 5 of Dark Hall capable of causing reverb runaway. From version 8.2 onward, ROM checksum diagnostics improved, with all serial communications code and the checksum program in the first SBC ROM, so if that ROM works, errors on the others get reported. Each ROM's checksum matches its ROM number.

The environment spec: operating range 0 to +35°C, storage −30 to +75°C, relative humidity to 95% without condensation. The LARC's cassette interface cable is a DIN-5 180° part. The mainframe-to-LARC cable is a DE-9 with a documented pinout: chassis/shield ground, receive and transmit data, transmit common, isolated supply voltage, receive common, and isolated supply ground.

By the mid-1980s the field was crowding. Mix (May 1985, p.38) ran the 224X with LARC alongside the Ursa Major BX32 and the Yamaha REV1 with its remote control unit in a roundup of the category. The 224X had no single killer spec. What it had was four transformer-isolated outputs, a 50-foot console cable, dynamic decay that reshapes the tail, and a cassette interface for keeping your work.

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