Pendulum Audio ES-8
Tube Limiter
 by Michael Cooper - MIX June 2001

   Rather than trying to recreate vintage tube gear, Pendulum Audio designs tube processors that incorporate modern, extended-bandwidth, Class-A circuit designs. Both the MDP-1 tube preamp ($2,495) and the ES-8 tube limiter ($3,495) are 2U, dual-channel units that feature transformerless outputs, low noise and a frequency response from below 20 Hz out to 65 kHz (75 kHz for the ES-8). Classy aesthetics, impeccable front panel screening, positive-action knobs and switches, gold-plated I/O connectors, and large, illuminated ANSI VU meters suggest the rigorous attention to quality that lurks below the hood. There you'll find gold-plated switch/relay contacts and tube sockets, polypropylene caps, metal film resistors and custom toroidal power transformers with hum-blocking shields. On both units, the chassis is ventilated through the top and side panels.

ES-8 Variable Mu Tube Limiter

The ES-8 is basically the same device as the Pendulum 6386 Tube Limiter, except that the ES-8 employs two 6ES8 tubes (one per channel) for gain control in lieu of 6386 tubes, which are in increasingly short supply. The dual-channel ES-8 offers the same compression curves as the Fairchild 660 and 670, but the ES-8 departs from those vintage designs in that a Class-A, solid-state makeup gain stage is used to drive its transformerless balanced outputs. Fast and Manual modes complement the six 'Fairchild' presets.

Inputs are via balanced XLR and 1/4-inch TRS phone jacks, wired in parallel. Outputs are via balanced XLR and unbalanced 1/4-inch phone jacks, also wired in parallel. A sidechain insert is provided for each channel on 1/4-inch TRS jacks (tip is send, ring is return), enabling frequency-sensitive processing applications such as de-essing. A Power switch (serving a soft-start warm-up circuit) and detachable three-prong AC cord round out the unit's rear panel.

As one would expect from a tube limiter, the ES-8 does not offer a ratio control. The compression characteristic is soft knee, with a smooth transition from compression to limiting as you hit the device harder. The ES-8 can provide up to 12 dB of gain reduction.

Continuously variable rotary knobs provide control over input attenuation, output gain boost/cut and threshold. The unit is optimized for +4dBu nominal levels. Maximum makeup gain is set at 12 dB at the factory, but you can adjust trims inside the chassis to increase the output control's maximum boost to 30 dB.

A three-way rotary switch lets you choose between three compression modes for each channel: Fast, Presets or Manual. Fast mode features fixed 0.5ms attack and 50ms release times.

The Presets mode activates a six-position rotary switch that implements different "Fairchild" presets. The first four presets offer release times of 0.1 second, 0.3 second, 1 second and 2 seconds, respectively. Presets 5 and 6 provide program-dependent, two-stage release times ranging between 1 to 4 seconds for preset 5 and 5 to 20 seconds for preset 6. In both presets 5 and 6, an initially quick release time is followed by a longer decay back to zero gain reduction. Attack times range from 1 to 4 ms for all six Fairchild presets.

Switching the ES-8 to Manual mode activates continuously variable attack and release rotary control knobs that are provided for each channel. Manual attack times range from 1 to 100 ms. Manual release times range between 0.1 and 2 seconds.

Separate rotary controls for each channel switch the VU meters to show input, output or gain reduction levels. Independent hard bypass switches are also provided for each channel. The ES-8's two channels can be operated independently or linked via a front panel switch. When linked, channel 1's settings control thresholds, all dynamics processing (modes and attack and release times) and bypass switching for both channels. Only the input, output and meter mode controls remain independent when the channels are linked, a logical arrangement.

My first test of the ES-8 was on arpeggiated acoustic guitar, played with a flat pick. Switched to Fast mode, the ES-8 sounded outstanding. The processed track was utterly devoid of audible amplitude modulation artifacts with 3 dB of gain reduction showing on the meters. (Peak gain reduction levels were obviously higher than what the VU meters showed.) The ES-8 produced a smoother timbre than most compressors I've heard in this application. Even with 7 dB of gain reduction, amplitude modulation artifacts were barely audible.

Fast and Manual modes provided great dynamics control for lead vocals. And pushing the ES-8 hard in Manual mode, I co-axed wonderfully warm, dense and crunchy tones out of my '62 Strat. The ES-8 also performed well on kick and snare drums, although a tube limiter is too slow to give you explosive UREI 1176LN-type snare sounds. Disappointingly, the ES-8 lent a tone to electric bass that was a little too soft--almost cottony--for my tastes.

The program-dependent Fairchild presets worked best for stereo bus compression. The ES-8's dynamics processing was laudably transparent. The unit lent a slightly euphonic, softer sound to the mix, while perfectly preserving spectral balance. The harder you hit the ES-8, the creamier it sounds. Purists might bark at me, but 8 to 10 dB of gain reduction on a stereo mix sounded great.

The only big beef I have with the ES-8 is that its inputs lack headroom. Pumping +26dBu mixes into the unit from my 02R's analog outputs, I had to lower the input levels about 8 dB down from unity to avoid audible distortion. [DESIGNER'S NOTE: This is EXACTLY what the input attenuator is for! You can, in fact use the input control to change the texture of the sound, by controlling how hard the input transformer and input tube are driven. If you routinely work with +26dBu input levels and use large amounts of gain reduction, the range of the Output level can be internally adjusted for up to +30dB of makeup gain. The output stage can drive up to +32dBu without distortion]. I should also note that the ES-8's +4dBu gain structure does not accommodate -10dBV levels very well, as the input control is strictly an attenuator. For most pro tracking applications, these issues should not be a problem.

The ES-8 is a clean, transparent tube limiter that performs admirably on the acid test for compressor/limiters--percussive, broadband program material. The unit is not heavily colored, lending more of a soft sound, rather than bursting with overtones. Its only weaknesses are its limited headroom at input and practical incompatibility with -10dBV systems. Boasting a plethora of features and elegant looks that more than justify the $3,495 price, the ES-8 is bound to find a home in many pro studios.

Pendulum Audio, PO Box 339, Gillette, NJ 07933; 908/665-9333;;

Michael Cooper is a Mix contributing editor and owner of Michael Cooper
Recording in beautiful Sisters, Ore.