Pendulum OCL-2
Electro-Optical Tube Compressor/Limiter
 by Eddie Ciletti - EQ February 2000

Quite literally "out of the blue" comes a new line of products from a company that once made 'only' an acoustic guitar preamp. The OCL-2 is an optical compressor / limiter with a minimal, Class A signal path consisting of two tubes per channel. (List Price: $2795) It is so minimal, that there are no input or output transformers even though XLR connectors get you the old 'in-out.'

The beauty of working with the OCL-2 as well and with its designer, Greg Gualtieri, is that both are remarkably open and flexible. Translation: There are a number of options, including balanced I/O and passive side-chain EQ filters. Mastering engineers and tweak heads take note: many of the control pots can be 'customized' to reflect user preferences such as Attack and Release ranges.

After an extensive interview, I learned that Mr. Gualtieri's design philosophy is derived from his need to capture acoustic guitar in the most transparent way possible. He is, however, not so much of a purist as to scoff at compression. Classic vintage signal processors are not always clean enough - nor are they in such great condition after time and abuse to justify current market prices. Greg originally created both the OCL-2 as well as the 6386 Compressor / Limiter for his own personal studio.

WEIRD (but cool) SCIENCE

The Pendulum OCL-2 is not a clone of the Teletronics LA-2A. As a former physicist for Bell Labs, Mr. Gualtieri knows how a photo resistor works at the molecular level having devised a proprietary method of taming the unruly optical beasts to a previously unattainable level of consistency. As such, the OCL-2 inspires confidence as a stereo unit that no other optical unit can match and then some.

It is hard to make traditional optical limiters sound bad. Without Attack and Release controls, users are limited to the natural characteristics of the optical parts, which just happen to be perfect for voice, guitars and bass - gentle enough to massage a stereo mix but not damage it. Other modern optical boxes like the Joemeek have added Attack and Release controls that go beyond normal to create interesting near-backwards effects. The controls on the OCL-2 are more effective (without the effect), in part because of the proprietary tweak that only Pendulum has.


Science aside, the OCL-2 has a three-position MODE switch - labeled FAST, PRESETS and MANUAL. The first two preset disable the Attack and Release controls. FAST is as FAST does. In this mode, the OCL-2 gets about the most sonic agility possible from an optical device.

Four of the Six PRESETS were originally modeled from the popular Fairchild Limiter. The last two presets are 'Program Dependent', which is to say that their response is more akin to a human 'riding the gain' and so less obviously processed. MANUAL mode turns on the Attack (1mS to 40mS) and Release (.1S to 2S) controls.


A VU Meter can indicate apparent 'loudness' better than a bargraph-style Peak Meter (unless the latter can simultaneously indicate peak and average levels). Instruments such as voice and bass have a nearly identical peak-to-average ratio, a perfect match for accurate display via VU meter. (The exceptions would be 'P-popping' consonants and 'snap happy' electric bass strings!) Conversely, transient-intense instruments such as drums and tambourine might deflect a VU meter only as high as ~5dB, but the peaks can be 10-dB to 15-dB higher. Analog tape machine users learn this lesson very quickly!


The OCL-2 was evaluated at the same time as the Pendulum 6386 Tube Limiter even though the two reviews appear in separate issues. (See the 6386 review in the December 1999 issue). The units were daisy-chained along with a Great River transformer-less mic preamp and the TASCAM DA-45HR 24-bit DAT recorder. I was completely comfortable using them together with no fear of signal degradation and so thankful for the BYPASS switches, which are not common on vintage products (and even some modern units). Having both units in the signal path made the comparison of identical settings quite easy. With slow attack and fast release the two models behaved as twins, but in FAST mode, the 6386 is more responsive.


Stereo program was the first signal passed through the OCL-2 because that is my acid test. Pass the test and you know the unit can handle individual tracks with ease. The LA-2A and the LA-3A were most notable for their transparent approach to dynamics processing. The OCL-2 goes two steps further by being more sonically transparent (no input or output transformers on a 'stock' unit) and far more versatile in terms of Attack and Release parameters. This will be of particular interest to those who wish to capture vocals, or any acoustic instrument, with the least amount of added color while still having equally transparent control over dynamics variations.

With the luxury of having the two models at the same time, I set the OCL-2 for a Slow Attack and Fast Release (my personal default) followed by the 6386 in FAST mode (as a peak limiter). My heavy-handed visuaî setting for the 6386 had lots of meter movement in Gain Reduction mode. To fully appreciate the FAST mode, however, more conservative settings of less than 1-dB of meter movement (2dB for the OCL-2) yielded such a profound sonic improvement that the 6386 review served as my VU meter refresher course. The combination of both units on a stereo mix was killer. (And this is as close to 'born again' as I will ever be!)

NOTE: Mention of the meter's response time appears on page four of the manual. It also deserves ìhonorable mention on the first page, where front and rear panel layouts, plus a quick summary of each control (a simple yet brilliant move) serve as a convenient and quick reminder.


Unlike the LA-2A (and especially the ADL clones), the OCL-2 has a very flat detector circuit, which means the unit equally processes ALL frequencies. One approach is not better than the other although I personally prefer a weighted detector circuit, one that 'hears' in a similar non-linear way to the human ear. (Through experimentation with side-chain equalization, I have found that a broad 6-dB boost centered at 2.5kHz works well for many applications.) Pendulum sells a TRS side-chain insert plugs with a passive RC network customizable to a user's needs. Very Cool!


Though not as quiet as the 6386, the OCL-2 has gobs of headroom. (Maximum out is +35 dBu into a hi-Z load, +24dBm into a 600-ohm load.) Maximum gain reduction is 27 dB. The OCL-2 is always open and airy, never harsh or muddy. This was made even more apparent on the very last test narration clearly showing that the OCL-2 has feet planted in two worlds, satisfying the passions of the sonic purist along with the needs of audio control freaks.

For the audiophile / minimalist, the plain and simple signal path, using high quality components (gold switches, polypropylene caps) is most reassuring. For the knob needy, no optical signal processor can match its control range. The Pendulum OCL-2 is not 'Rehashed Retro', but Enhanced Vintage Technology.


EQ Lab Report

MANUFACTURER: Pendulum Audio, Inc.; PO Box 339, Gillette, NJ 07933; Vox: 908-665-9333 Web: e-mail: info@

APPLICATION: Audio Dynamics Processing

SUMMARY: Stereo (or Dual-Mono) Optical compressor / limiter with three Response modes: FAST, Preset (4 'normal' plus 2 'program dependent') and Manual (front panel Attack / Release).

STRENGTHS: Minimal Class A signal path maintains sonic purity. In addition to a BYPASS switch, the output is normally bypassed until the unit warms up and voltages are stabilized.

WEAKNESS: The Gain Reduction Meter needs (and may get) expanded range to more accurately reflect the amount of processing when in FAST mode.

PRICE: $2795.00