The Pendulum Audio OCL-2 is a two-channel electro-optical compressor/limiter designed, in the maker's words, "for the utmost in transparency, detail and versatility"1. It is a rack unit rather than a pedal: a 2U enclosure that runs on mains power, aimed at players and engineers who want studio-grade compression in the signal chain. Pendulum Audio says its custom opto cell provides "fast, invisible compression without the artifacts and sluggish response inherent in vintage" opto designs2.
The signal path is analog throughout: a custom optical input attenuation network sits in front of an all-tube Class A gain stage, with a transformerless output1. Pendulum Audio describes the result as "an open, detailed sound with an expanded sound stage and clarity that can only be achieved with modern tube circuitry"1. The unit was introduced in 1998, and Pendulum Audio's spec sheet calls it "a modern classic" since then2. It is handcrafted in the USA1.
How it works
The OCL-2 is an opto compressor: a light-dependent element controls how much the signal is turned down, and a tube stage brings the level back up. The maker's short signal path design puts the optical attenuator in front of the tube gain stage1. The compression curve is a soft-knee design with a fully adjustable compression ratio1.
Key specifications from the maker:
| Specification | Value |
|---|---|
| Input sensitivity | +4dBu1 |
| Input impedance | 10Kohm1 |
| Frequency response | -1.0dB at 8Hz and 145kHz with 10Kohm output load1 |
| Noise | less than -78dB below +4dBu output (Output at 0dB); less than -75dB (Output at +20dB)1 |
| Distortion | less than 0.05% THD+N, 20Hz to 10kHz1 |
| Output | +35dBu into 10Kohm load, +24dBu into 600 ohm load1 |
| Polarity | XLR connectors pin 2 hot1 |
Fast, Preset and Manual modes
The sidechain offers three operating modes1, and this is where the OCL-2 differs from simpler opto compressors with fixed behavior.
- FAST mode: the optical cell operates with very fast attack and release times, peak-averaged by the rapid operation of the cell. Pendulum Audio says it is "remarkably free of pumping artifacts even at high compression levels"1.
- PRESET mode: six classic attack/release settings optimized for program compression, including two with program-dependent release times1. The presets are 0.1s, 0.3s, 1s, 2s, 1 to 4s and 0.5 to 20s (program dependent)1.
- MANUAL mode: total control over attack and release, which Pendulum Audio calls "particularly useful for creative compression effects or for processing bass guitar"1. Attack is variable from 1.0ms to 40ms and release from 0.1s to 2s1.
Controls and connections
| Control | What it does |
|---|---|
| Meter | Selects input level, gain reduction or output level, referenced to +4dBu = 0VU1 |
| In/Bypass | Hard bypass of input signal to output connector1 |
| Link/Split | Links channel 1 and channel 2 for stereo operation1 |
The two channels are completely independent, with hard bypass switches for each channel and sidechain inserts for frequency-dependent compression and de-essing1. The optical cells are custom matched for precise stereo balance1.
The OCL-2 runs on mains power (120Vac, 30W, with a 240Vac option) and uses regulated high-voltage internal supplies with soft-start warm-up and output muting1. It is not compatible with pedalboard power supplies or batteries.
Where it came from and what came after
The OCL-2 dates to 19982. Its fast opto cell also lives on in other Pendulum Audio designs: the maker's DS-500 page describes using "the fast opto cell from the OCL-2 as part of a triggerable LC notch filter" for de-essing3. Players comparing rack options can also look at the Pendulum Audio Quartet and the Pendulum Audio OCL-500, a 500-series format compressor from the same maker.
For players coming from stompboxes, the OCL-2 is a different animal from a compressor pedal: line-level XLR inputs and outputs, a 2U chassis, and a sidechain with three modes and inserts. Bass players in particular may find the Manual mode's slowest attack and release settings useful, as the maker itself notes the mode suits bass guitar processing1.
Videos
Retrosonic Pro Audio
Questions
Is the Pendulum Audio OCL-2 a tube compressor?
Yes. The OCL-2 uses a Class A vacuum tube signal path with a transformerless output, built around two 6072A and two 6922 tubes. The gain reduction itself comes from a custom electro-optical attenuator placed in front of the tube gain stage, so it is an opto compressor with an all-tube audio path.
Can the OCL-2 be used in stereo?
Yes. The two channels are completely independent, and a Link/Split switch links channel 1 and channel 2 for stereo operation. Pendulum Audio matches the custom optical cells for precise stereo balance, so the two channels track each other when linked.
What are the attack and release ranges in Manual mode?
In Manual mode the attack time is variable from 1.0ms to 40ms and the release time is variable from 0.1s to 2s. Pendulum Audio describes this mode as useful for creative compression effects or for processing bass guitar.
What voltage does the OCL-2 run on?
It runs on mains power: 120Vac at 30W, with a 240Vac option. Internally it uses fully regulated +300Vdc, +12.6Vdc and ±15Vdc supplies with soft-start warm-up and output muting. It is not a battery or pedalboard power device.
How many rack spaces does the OCL-2 take?
It takes two rack spaces (2U). The enclosure measures 19 x 3.5 x 12.5 inches (48.2 x 8.8 x 31.8 cm) and weighs 14 lbs (6.4 kg).
Sources (3)
- OCL-2 - Pendulum Audio, Pendulum Audio
- OCL500-Brochure.pdf, Pendulum Audio, 2008-10
- DS-500 - Pendulum Audio, Pendulum Audio
