Lexicon 300L

The 300L is a mainframe that can't be serviced in the field, ships with a proprietary remote as standard, and has a 20dB gain trim in 0.1dB steps. It's a studio reverb that expects you to work the way it works.

Overview

The 300L is a Lexicon digital effects processor. The first thing the period press noticed was what came in the box. EQ Magazine (May 1995, p.16) reported that the 300L was a new version of the still-available 300 processor, and that every operation runs through the LARC - Lexicon's proprietary remote controller - which ships with the standard configuration. It was also offered as a mainframe only. That suits rooms that already had a LARC on the console and just needed another engine behind it.

The converter stage is where the 300L makes its case. The A/D side accepts balanced XLR on pin 2 high, with an input impedance of 50kΩ unbalanced and 100kΩ balanced, and a gain switch that flips between a 0dB position covering +2dBu minimum to +20dBu maximum full scale, and a +16dB position covering -14dBu minimum to +4dBu maximum. That second setting is the one that matters in a real room — it lets a quiet source hit full scale without an outboard preamp in front of the converter. Common mode rejection is 60dB minimum from DC to 2kHz and 40dB minimum from 2kHz to 20kHz, which is the kind of balanced input design that holds up next to tape machines and consoles rather than a shelf.

Frequency response follows the sample rate: 10Hz to 21.5kHz at +0.2dB at 48kHz, 10Hz to 20kHz at 44.1kHz, and 10Hz to 14.5kHz at 32kHz. Phase linearity is +5 degrees from 10Hz to 20kHz and frequency independent. Analog input to digital output delay is 0.75mS. Crosstalk is held to 80dB maximum from 10Hz to 20kHz, signal-to-noise is 90dB minimum A-weighted, and both THD and SMPTE intermodulation distortion are 0.01% maximum across 10Hz to 20kHz. Dynamic range is 90dB minimum. Pre-emphasis is switchable between 15µs and 50µs, and the gain control offers 20dB of range in 0.1dB increments.

The D/A side is the stronger half. Output is balanced XLR on pin 2 high with a 75Ω output impedance and a full scale output level from -2dBu to +18dBu. Frequency response, phase linearity and the stereo crosstalk figure all track the A/D section. Elsewhere the output stage tightens up: crosstalk drops to 90dB maximum, signal-to-noise rises to 100dB minimum A-weighted, and THD and SMPTE IMD both hold at 0.01% maximum. Dynamic range stays at 90dB minimum. Digital input to analog output delay is 1.8mS. De-emphasis mirrors the input side at 15µs and 50µs, with the same 20dB in 0.1dB increments gain control. For the whole analog-to-analog path at 48kHz, the figures are 10Hz to 21.5kHz at +0.2dB with 80dB maximum crosstalk, 90dB minimum A-weighted S/N, 0.01% maximum THD, 0.01% maximum SMPTE IMD, and 90dB minimum dynamic range.

The digital interface is professional-grade and unambiguous: balanced female XLR digital input, balanced male XLR digital output, conforming to AES 3-1992 (ANSI S4.40-1992). That's the AES/EBU standard, not a consumer S/PDIF variant, and it tells you the 300L was built to sit in a digital chain rather than at the end of one.

The service documentation is blunt. The DSP board cannot be troubleshot in the field, and symptoms pointing to DSP failure mean contacting Lexicon Customer Service. The 300L is a mainframe you send back to the factory, not a box you fix on the bench. The service procedure starts with the obvious: top cover off (three screws per rack ear, three per side, one at the front of the cover, one upper-center on the rear panel), then an inspection for burnt smell, mechanical damage, loose components, and the relay clicks that should be audible on power-up. Fuse values are documented per line voltage. 100/120V uses .5A, .5A, 3.15A, and .500A (3AG) across F1, F2, F3, and F5. 230V uses .5A, .5A, 3.15A, and .250A. The XLR connectors are checked for tightness with a dedicated "XLR Lock Screw Driver" turning the lock clockwise, and ribbon cables are checked for proper seating.

The troubleshooting philosophy in the manual is genuinely useful, and it's the kind of thing that separates a 300L from a box with a service department that doesn't care. One channel bad means the power supplies, system timing, and digital circuitry up to the oversampling filters are all fine — you can use the working channel as a reference and trace the fault along the analog path. Both channels bad points to something common: a shared component, a power supply issue, or a timing problem. The manual also flags cables and connectors as the natural weak point, noting that vibration can break strands, oxidation and flux contamination can make connections intermittent or resistive, and poor seating at assembly shortens long-term reliability. The Host-to-DSP continuity table is included as a minimum check, with the caveat that if those lines check out and you're still getting power-up errors, there's a legitimate circuit problem — but inspect every cable before, during, and after removal anyway.

The power-up sequence is documented. The LARC should display LEXICON, then MAINFRAME RESET, then LEXICON 300L VX.XX, then LARGE HALL SG:SET P 1. If LARGE HALL doesn't appear, the manual's fix is to press BANK, 1, PROG, 1.

Period advertising leaned on the control surface and the ecosystem rather than the converter specs. Mix Magazine (December 1995, p.89) ran Lexicon's copy positioning the 300L as the newest addition to the company's world-class digital effects systems. It also noted that owners of a 300L, 480L, or 224XL could add multi-machine LARC control via the LR-4. Studio Sound (December 1995, p.35) carried the same campaign copy, framing the 300L as a new version of the award-winning 300.

The Sound on Sound review of the PCM90 (May 1996, p.84) offers a cross-reference for placing the 300L in the line. The reviewer noted that the PCM90 borrowed algorithms from the 480L and 300L, and called out the 300L's Ambience algorithm as one of the most notable hand-me-downs.

For a buyer today, the 300L is a mainframe with a specific service posture. The DSP board is not field-serviceable, the unit wants a LARC to be useful in its standard configuration, and the digital I/O is AES/EBU on XLR. The analog front end is solid: the +16dB gain switch position, the 0.1dB gain trim, the AES 3-1992 digital interface, and the 100dB minimum A-weighted D/A signal-to-noise.

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Lexicon 300L

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