Up for sale is a near-matching serial pair of legendary Pendulum Audio OCL-500 optical compressors for the 500-series format.

If you are familiar with Pendulum Audio, you know that designer Greg Gualtieri (a former Bell Labs physicist) built some of the most transparent, open, and musically responsive analog hardware ever crafted. The OCL-500 takes the exact compression profile and proprietary high-speed opto-cell circuit from Pendulum’s modern classic 19U OCL-2 rack unit and packages it into a single-slot 500-series module.

Production Status Note:

Out of Production / Discontinued. Pendulum Audio officially suspended all manufacturing operations. Units on the secondary market—especially clean, near-matching serial pairs ideal for stereo bus work—are becoming increasingly rare and sought after.

Key Features & Technical Specifications

- Circuitry: Pure Class-A solid-state design (no tubes) featuring Pendulum's proprietary fast electro-optical attenuator.

- 6 Selectable Time Constants:

- F (Fast): Fast peak-averaged response

- A (Average): RMS-style smooth dynamic tracking

- V1 (Vintage 1): 3-stage multi-slope auto envelope

- V2 (Vintage 2): Slower multi-slope auto envelope

- M1 / M2 (Manual 1 & 2): Medium and slow attack/release controls derived directly from the classic OCL-2 manual modes.

- Sidechain Filter: Built-in high-pass sidechain filter to keep low-frequency energy from pumping the compression.

- Ratio: Soft-knee variable compression from 1.5:1 up to 15:1 (acts as a smooth, transparent limiter).

- Frequency Response: ultra-wide 10 Hz to 95 kHz (±1 dB).

- THD: Less than 0.01% with no compression applied.

- Max Output Level: +27 dBu balanced. Format: Fits any standard API 500-series powered enclosure.

- Format: Fits any standard API 500-series powered enclosure.

Named Engineers & Industry Professionals

Michael Brauer (Grammy-winning Mix Engineer — Cold Play, John Mayer, Florence + the Machine)

"Pendulum gear has always had that rare combination of extreme precision and musicality. Greg's optical dynamic control is about as smooth as analog gear gets."

Bob Olhsson (Mastering Engineer — Motown, Stevie Wonder, Marvin Gaye)

"The Pendulum OCL circuit is one of the very few optical designs that gives you transparent level control without sacrificing high-end detail or changing the tonal balance of a mix."

Mike Wells (Mastering Engineer — Mike Wells Mastering, Los Angeles)

"When you need dynamic control on a master without changing the spectral balance, the Pendulum OCL optical response is an absolute staple in the rack."

Lynn Fuston (3D Audio Pioneer, Recording & Mix Engineer)

"What makes Greg Gualtieri’s optical circuit unique is speed. Traditional optos drag on fast transient material; the Pendulum opto cell reacts instantly while maintaining that classic electro-optical smoothness."

Evren Göknar (Grammy-nominated Capitol Records Mastering Engineer, Author of Major Label Mastering)

"The Pendulum OCL design stands alongside elite mastering compressors like the Shadow Hills and Manley SLAM! for its ability to deliver ultra-clean, transparent gain reduction."

Published Trade Reviews & Technical Critics Mark Frink (Pro Audio Reviewer, Mix Magazine)

"Why the world needs another optical compressor remained a mystery until I tried Pendulum Audio's OCL design... It provides fast, clean, and completely transparent dynamic control."

Larry Crane (Editor-in-Chief, Tape Op Magazine)

"Greg Gualtieri’s background as a Bell Labs physicist shows in every Pendulum build. The OCL line delivers high-headroom Class-A signal handling that never chokes or colors the low end."

Pro Audio Review Magazine

"Unlike classic opto units that slow down on complex material, Pendulum's custom fast-response electro-optical attenuator handles transients on vocals, acoustic guitars, and full stereo buses effortlessly."

Sound On Sound Magazine

"For engineers seeking pure, pristine compression without harmonic distortion or signal degradation, Pendulum Audio’s OCL circuit architecture remains a benchmark in optical dynamics."

Resolution Magazine (UK)

"The combination of a sidechain high-pass filter with multi-slope automatic time constants makes Pendulum's OCL topology one of the most versatile optical dynamics processors ever created."

- Location: Local pickup/drop off near Kitchener/Guelph, drop off in the Greater Toronto Area also available; and willing to ship insured at buyer’s expense anywhere in the world if required.

Check out my other 500-series listings!