Pendulum Audio Quartet II, Mercenary Edition
 by Russ Long, Pro Audio Review, September 2005

   Pendulum's Greg Gualtieri is one of those people who insist on doing everything right. I'm a long-time fan of the quality construction and superior audio performance of his products. I bought the Pendulum 6386 after reviewing it several years ago and then a couple of years later I had the opportunity to review the Pendulum Quartet which also blew me away. I was anxious to check out the new Quartet II, Mercenary Edition ($5,250). Designed with the input of Mercenary Audio's Fletcher, it includes several additional options over the Quartet that allows the user to shape the audio character for maximum musical flexibility and, in many ways, it is the perfect compliment to the Quartet (which is still being manufactured).

   The Quartet II features the tube mic/DI preamp from the Pendulum MDP-1, the Delta-Mu tube compressor/limiter from the Pendulum Audio ES-8, a three-band inductor-based passive tube EQ low shelving, a mid cut and high peak bands with adjustable Q, and an aggressive mode, and peak limiter with JFET and MOSFET modes. The box features a tube-based signal path with pure Class A, high-voltage circuitry. Each of the Quartet II's components are separate entities that can be independently accessed via the rear panel.

   In order to yield the highest quality sound possible, the 12.5-inch deep, two rack-space Pendulum Quartet II uses gold-plated switch contacts, I/O connectors and tube sockets as well as polypropylene caps and metal film resistors (pairs matched to 0.1%). It uses two ECC83/12AX7A tubes for input and two 6922/6DJ8 tubes for output. The gain control tube is a 6ES8/ECC189. On the rear panel of the 14.5-pound box, a female XLR connector provides microphone input and a 1/4-inch jack provides DI input. The microphone preamp's input impedance is 1500 ohm or 10k ohm (transformer balanced and floating), the line input impedance is 100 Kohm and the instrument impedance is 10 Mohm on the front panel 1/4-inch jack and 1 Mohm on the rear panel jack.

   The rear panel's nine 1/4-inch jacks located between the input and output connectors are used to patch in and out of the mic/DI preamp, EQ, compressor and limiter or to insert other equipment into the signal chain. A male XLR connector wired pin two hot provides the Quartet's transformer balanced output and a 1/4-inch TRS jack provides unbalanced output. The Quartet gets its power through an IEC socket that connects to a standard three-prong IEC power cable (included). The voltage selector switch allows the box to easily be switched between 115 volts and 230 volts. To insure the longest possible tube life, the Quartet II's soft start sequence gently applies power to the tubes and stabilizes the circuit before engaging the outputs.

   The Full/Focused switch in the Mic/DI preamp section switches between two drastically different sounding input transformers and loading options. The Full setting has a ratio of 1:5 and the Focused setting ratio is 1:10. I found that in most instances, I preferred the sound in the Focused position. The only exception to this was recording acoustic guitar (strummed not picked), violin and viola. The 1500/10K switch changes the load impedance seen by the microphone. The DI Input switch selects between Instrument (10 Mohm at the front 1/4-inch jack, 1 Mohm at the rear jack) and line (100 Kohm) inputs. The MIC/DI switch selects the MIC input (via the rear panel XLR input connector) or the DI input signals (via the front or rear 1/4-inch input jack). The +48V switch activates 48 volt phantom power and the 0/-20 switch inserts a 20 dB pad before the microphone's input transformer. The ± switch reverses the phase of the microphone signal and the Lo Cut switch applies an 18 dB/octave low frequency rolloff at either 75 Hz or 150 Hz. The Gain control adjusts the gain in 3dB steps from +33 dB to +63 dB for the full mic input, +40 dB to +70 dB for the Focused mic input, +20 dB to +50 dB for the DI instrument input, and 0 to +30dB for the DI line input. The Output control adjusts the output level of the preamp stage. By varying the ratio between the gain and the output control, the harmonic content of the preamp can be varied.

   The three-band tube Passive/Aggressive Equalizer is a modern take on the classic inductor-based passive EQ. It features simultaneous Lo Shelf boost and cut, Mid Dip and Hi Peak bands. The Hi Peak provides up to +20 dB (bandwidth-dependent) of gain from 0.8 kHz - 18 kHz. The Mid Dip provides up to ­20 dB (bandwidth-dependent) from 200 Hz - 800 Hz. The Lo band features up to 20 dB of shelving from 20 Hz - 120 Hz. The EQ - µ / µ - EQ switch places the EQ before or after the compressor. When the EQ is activated, a blue LED is illuminated. When the Aggressive mode is activated, the saturation of the EQ circuit is increased to add harmonic content (nice!).

   The delta-mu compressor has the classic compression profile of the Fairchild 660 and 670 limiters. It features separate threshold and output (up to +15 dB of gain makeup) controls. The Mode switch selects the mode of compression. The five options include: Fast and Faster (both peak-averaged), Average (rms detection), Vintage (program dependent attack and release times), or manual (attack 1 ms - 100ms, release 0.1-2s). The Sidechain Lo-Cut switch reduces detector sensitivity below 150 Hz.

   The new JFET/MOSFET Peak Limiter has JFET and MOSFET modes for two different characters of peak limiting. Unlike other designs, the peak limiter adds no appreciable distortion below threshold. In this section, the Ceiling function determines the maximum output level for peak limiting and the JFET/MOSFET selects the mode of FET peak limiting. The nine-segment LED display indicates the amount of peak limiting applied to the signal. The Compressor/Output switch determines whether the illuminated VU meter indicates level of gain reduction or the output signal level. The meter is electronically isolated from the signal path and is calibrated to 0VU = +4dBu (1.23Vrms).

In Use
   I had repeatedly returned to the vocal sound on a rock project that I was mixing a few months back and just couldn't get it right. Over the period of a week, I had literally tried everything in my arsenal and nothing was nailing the aggressive sound that the artist and I were looking for. That was the day the Pendulum Quartet II arrived. I hooked it up and was immediately amazed. When the artist walked in I simply told him to have a listen, I didn't want him to have any preconceived notions. At the end of the first chorus he stopped the playback and yelled, "You got it, that's the vocal sound!" Since then, every time I've put the box to work on vocals I've been pleased. I used it to record both male and female vocals with the Sony C-800G, the Blue Microphones Cactus and the Brauner VM-1KHE and had wonderful results in every instance. The box also does an amazing job adding tube character to vocals recorded through solid state microphones. As was the case with the Quartet, I had good results using an XLR to 1/4-inch adapter to plug the mic into the rear panel DI input and completely bypass the input transformer. In most instances I prefer the sound of the 'focused' transformer on lead vocals and the 'full' transformer on backing vocals.

   I recorded bass guitar through the instrument input and ended up with a big, phat tone that wasn't lacking in presence and definition. The box coupled with an Earthworks SR-25 did a wonderful job capturing the sound of my Taylor acoustic guitar. The top-end had a wonderful sparkle and sheen without ever sounding harsh or edgy and the bottom end was rich and big. The box also worked extremely well for recording electric guitars with a Royer R-122.

   I had superb results using the box to record kick drum with a Heil PR-40, snare drum with a Shure SM-57, hi-hat with a Neumann KM-86i and shaker and tambourine with a Royer SF-1. There were several instances where I used the mic pre in one signal path, the EQ on another and the compressor and limiter on another. Each section performed flawlessly. The ability to simultaneously use each of the four components completely independent from the others is a wonderful thing. This is not possible with most of the all-in-one boxes that I've encountered. I occasionally found that I needed to supplement the Quartet II's EQ with a GML 8200. The Quartet II's EQ sounds wonderful but it is fairly limited so if extreme sonic manipulation is required it will likely require the addition of a more flexible EQ.

   The Pendulum Quartet II squashes a load of features, phenomenal sound, extreme flexibility, and a tube-based signal path with pure Class A, high-voltage circuitry into a single package. The box is a bit pricey but worth every cent.
Russ Long, a Nashville-based producer/engineer, owns The Carport recording studio. He is a regular contributor to Pro Audio Review.

Fast Facts
Applications: Studio
Key Features: Single-channel; preamp; delta-mu compressor; three-band EQ; limiter; 20 dB pad for preamp
Price: $5,250
Contact: Pendulum Audio at 908-665-9333,

+ Fantastic sound
+ Preamp, EQ, compressor and limiter can each be accessed individually

- Pricey