Technology

Pendulum Audio MDP-1 & ES-8

Rather than try to re-create vintage tube gear, Pendulum Audio designs tube processors that incorporate modern, extended-bandwidth, Class-A circuit designs. 8/01/2001 8:00 AM Eastern

Rather than try to re-create 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 variable Mu 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, 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.

TUBE MIC/DI PREAMP

The MDP-1 can be ordered with either Jensen 13K7 transformers or custom transformers for the balanced audio inputs. (My review unit had the Jensen transformers installed.) Each channel's audio path passes through one 12AX7A and one 6922 tube. On the rear panel, an XLR connector for each channel accommodates mic inputs, and unbalanced ¼-inch phone jacks service mic/line DI inputs. These DI jacks have a 1-megaohm input impedance when a DI input switch on the unit's front panel is set for instrument input. When this same switch is set for line input, the rear panel DI input jack's impedance becomes 100 kilohms, and a 20dB pad is inserted into the audio path. The circuit path is transformerless for all DI inputs.

Conveniently, the unit's front panel also features DI inputs on unbalanced phone jacks. When you insert a plug into a front panel jack, the rear panel DI jack for the same channel becomes disabled. The front panel DI jacks each have an input impedance of 10 megaohms for instrument inputs and, like the rear DI jacks, 100-kilohm impedance for line inputs. I found that electric bass tended to have a slightly tighter bottom but less top end “air” when plugged into a rear DI input, as compared to plugging in through a front panel jack. It's great to have such flexibility to get sounds.

The MDP-1's rear panel outputs are unbalanced XLR and ¼-inch phone jacks, wired in parallel. The transformerless, tube output stage can handle blazing output levels as hot as +35 dBu. A rear panel Power switch feeds a soft-start circuit that mutes the audio output and preserves tube life.

The MDP-1's front panel is replete with useful knobs and switches, yet it remains very user-friendly. Separate toggle switches are provided for each channel to enable 48V phantom power, switch in a 20dB mic input pad, flip the mic signal's polarity, and switch between mic and DI inputs.

Each channel sports a switched, rotary gain knob fixed in 3dB steps that controls the tube gain stage. The gain range spans 30 dB but varies for each type of input: +33 to +63 dB for mic input; +20 to +50 dB for DI instrument input; and 0 to +30 dB for DI line input. Additionally, continuously variable rotary knobs allow you to passively attenuate each channel's output level. By cranking the gain knob that serves the tube stage and lowering the output gain level, you can overdrive the tubes and introduce subtle distortion. This feature makes the MDP-1 a very versatile beast, allowing you to dial in a variety of sounds, from ultra-clean to slightly funky. I've heard cheaper units that offer tube overdrive topologies, and many make your tracks sound like bumblebees trapped inside tinfoil. The MDP-1, however, gives you that sweet splatter of harmonics you lust for.

Yet another rotary switch for each channel allows you to roll off the low end for mic signals at 10 different corner frequencies from 20 to 180 Hz, with an 11th setting for flat response. Finally, a three-way switch for each channel allows you to source the VU meters to show tube gain (pre-attenuator) or output level (post-attenuator) or to turn the meters off when you're pinning. Sourcing tube gain allows you to gauge whether or not you're overdriving the tubes and by how much.

My first test of the MDP-1 was on male lead vocals. This singer had a very woolly voice, for which my AKG TL-II was the perfect mic. But I've never heard my solid-state TL-II sound as good as this. The vocals were beautifully articulate, sweetly scintillating, tonally balanced and clear as a bell, yet eminently warm. The overall sound was lush, brimming with nuance and possessing great depth. I got similarly great results using a Lawson L47MP tube condenser mic on another vocalist.

On acoustic guitar, recorded with a spaced pair of B&K 4011 mics, I was, again, completely blown away. The stereo imaging was hands-down the widest I've ever heard with any mic pre. Transient response was outstanding, offering copious detail but without a hint of stridency. For comparison purposes, the MDP-1 was more understated in the upper bass/low mids than a Millennia HV-3 mic preamp, but, nevertheless, was much warmer sounding (love that glowin' glass!).

Next, I A/B'd the MDP-1's DI path against that of my super-pristine Aguilar DB 900 tube direct box a tough opponent. On electric bass, the DB 900 sounded cleaner and clearer with a sweeter tone. The MDP-1 sounded slightly honky and veiled in comparison, but also bigger, lusher and more aggressive. Overdriving the MDP-1's tube stage and daisy chaining into an Empirical Labs Distressor yielded a bawdy, burpy bass, gushing with overtones.

Next, I DI'd my '62 Strat. Again comparing to the DB 900, the MDP-1 at its cleanest settings produced a tone that had less air and nuance but fuller and creamier low mids, making for a beautifully mellow sound. Overdriving the MDP-1's tube stage to various degrees, I could get ultra-clean or subtly gritty tones. Interestingly, overdriving prerecorded ADAT tracks via the MDP-1's DI inputs (set to “Line”) yielded far more subtle results. And, without overdriving the tubes, the line inputs sounded basically neutral nothing added, nothing taken away.

Outstanding transient response, superior depth, superb spectral balance, unbelievably wide stereo imaging, extended frequency response, low noise and a lusciously warm sound make this fully featured and classy-looking mic preamp a great value at $2,495.

VARIABLE MU TUBE LIMITER

The ES-8 is basically the same device as the Pendulum 6386 Variable Mu Tube Limiter, except that the ES-8 employs six ES8 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 ¼-inch TRS phone jacks, wired in parallel. Outputs are via balanced XLR and unbalanced ¼-inch phone jacks, also wired in parallel. A sidechain insert is provided for each channel on ¼-inch TRS jacks, enabling frequency-sensitive processing applications such as de-essing.

As one would expect from a variable Mu 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 20 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 from 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.

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. Pushing the ES-8 hard in Manual mode, I coaxed wonderfully warm, dense and crunchy tones out of my '62 Strat. The ES-8 also performed well on kick and snare drums, although a variable Mu 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 taste.

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 Yamaha 02R's analog outputs, I had to lower the input levels about 8 dB down from unity to avoid audible 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; www.pendulumaudio.com.