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Empirical Labs EL9 Mike-E

Microphone Preamplifier & Compressor
Published February 2010
By Hugh Robjohns

Empirical Labs, purveyors of some of the most versatile compressors around, apply their dynamics expertise to a mic preamp.

American manufacturers Empirical Labs design a range of professional audio hardware and software products, but by far the company's best known are the Distressors — an intriguing range of digitally‑controlled analogue compressors that has been around since the mid 1990s — and the Fatso, essentially a valve (tube) and tape emulator. Their latest product is the Mike‑E, a single‑channel, solid‑state mic preamp with an integral compressor section, all digitally controlled, and offering some unusual facilities.

Guided Tour

The Mike‑E is housed in a 1U, rackmounting, black‑painted, steel case, with attractive blue screened legends around the front‑panel controls. The rear panel is marked clearly with white legends, and the interfacing starts on the left‑hand side of that, with an IEC mains inlet. The mains voltage, 230 or 115V AC, can be selected using an internal switch, and the line fuse is also internal, but the unit's lid can be removed by unscrewing the nine cross‑head screws holding it in place. Power consumption is a frugal 15W.

Moving to the right, the review model had a blanking plug over a hole that is provided to accommodate an additional output XLR for the optional Jensen output transformer, which was not installed. Next comes a pair of quarter‑inch sockets providing a side-chain input and side-chain control‑voltage linking for stereo applications with a second Mike‑E. Over at the right‑hand side are the input and output phantom-powered XLRs, each with an associated quarter‑inch jack socket. The two input connectors are wired in parallel (so phantom does appear on the jack socket), and feed a Lundahl transformer, but the Jensen or a larger Lundahl transformer, for better LF headroom, can be fitted as options. The input impedance is surprisingly low, at a nominal 600Ω, and the 10dB input pad is located before the transformer to avoid saturation with loud inputs. On the output side, the XLR is electronically balanced, while the quarter‑inch socket is unbalanced (tip connected to pin two of the XLR), and maximum output is a whopping +28dBu.

Between these XLR and jack connections there was another blanking plug on the review model, and this caters for an optional TRS socket, providing an unbalanced insert point between the preamp output and compressor input. This could be used to integrate an equaliser, perhaps, or to enable an uncompressed direct feed of the mic signal to be recorded alongside the main (compressed) output.

Internally, most of the electronics are mounted on a main circuit‑board occupying about three‑quarters of the floor space. Components are all standard (no surface mount here), with lots of integrated circuits, all of which have been defaced to hide their identification markings. Lots of sealed relays are in evidence for function switching, and the power supply is a linear design. The rear‑panel connectors are all mounted on the chassis, with wire links to the board, and most of the front‑panel controls are mounted on a couple of vertical daughterboards behind the panel, linked back to the main board on ribbon cables. Build quality looks good, so the Mike‑E should prove reliable.

The specifications claim a bandwidth of 3Hz to 200kHz with the compression and saturation (CompSat) section bypassed. The high end drops slightly, to 150kHz, with CompSat engaged, but I doubt anyone would notice! If the optional output transformer is installed, the bandwidth from that output is given as a very creditable 6Hz to 80kHz.

The front panel is quite sparsely populated, thanks largely to the advantages of digital control (push buttons take up much less space than rotary controls), although there are a lot of LEDs! Starting at the left hand side, a DI input socket automatically overrides any rear‑panel connections. This unbalanced input has an impedance of around 340kΩ and is intended for low‑level sources such as guitars and basses.

The rear panel of the Mike‑E.The input gain is adjusted with a pair of increment/decrement buttons, in 5dB steps from 60dB down to 10dB. A diagonal array of LEDs indicates the current gain setting, ranging from green at the low end, through amber, to red at the maximum settings. The company claim the Mike‑E has a 'super low noise' preamplifier, and the specs claim a 130dB signal‑to‑noise ratio at 40dB of gain, which is very good — although this figure was achieved with the inputs shorted rather than terminated with 150Ω (or 200Ω), which is the standard way (and which would produce a poorer specification, of course). There's no level meter, but a clip LED illuminates when there is a problem. With 20dB of extra gain available at the output control, an overall total of 80dB of gain can be dialled in.

The next panel section has two buttons. The upper one cycles through four options, providing an 80Hz, third‑order (18dB/octave) high‑pass filter on the output of the preamp section, or a polarity inverter just prior to the output driver — or both, or neither — with green and yellow LEDs to indicate the status. The lower button activates the 48V phantom power.

The bulk of the front panel is taken up with the CompSat compressor controls. The main rotary control, with a Distressor‑style knob, sets the amount of Drive into the compressor, while four push‑buttons configure the operating mode. The first toggles the external control‑voltage link on and off, and the pre‑emphasis/de‑emphasis circuitry on and off (red and yellow LEDs indicate the current setting). The next selects the compression ratio, cycling around six options, each indicated with more colourful LEDs: Bypass, 1:1, 2:1, 4:1, 8:1 and 'Nuke'. Bypass does as it says, while 1:1 essentially disables the compressor stage but leaves the saturation circuitry working. The straight ratios all have soft‑knee characteristics, so are fairly subtle in their response, while Nuke provides a limiter action and engages different attack and release characteristics to suit that application. The last two buttons adjust the attack and release time constants, each cycling around four options with yet more LED indicators. Attack options are 0.9, 2, 8 and 100ms, while release options are 50, 100, 250 and 500ms — although they all sound slower than the numbers suggest in practice. Arranged across the top of this section is a bar‑graph gain‑reduction meter, with eight LEDs spanning a 20dB range. Usefully, a small rotary mix control allows the compressed and direct signal to be blended for parallel compression effects.

I mentioned two additional circuits earlier which I should explain further. The switchable pre‑emphasis/de‑emphasis feature boosts the level of high frequencies ahead of the compressor/saturator and restores it afterwards. This means that high‑energy high‑frequency components will be more strongly affected by the saturation and compression processes, essentially soft‑clipping them in a musical and tape‑like way. The saturator is a soft‑clipping section that emulates the appealing effects of triode valve stages at low levels, progressing to a harder effect (achieved with germanium transistors) as the drive is advanced further. The resulting distortion can be varied from a tiny fraction of a percentage point up to about 15 percent, depending on the setting — so there's plenty of controllable coloration available. A pair of LEDs gives some idea of how hard this stage is working, with 'Warm' and 'Toasty' indicators!

The final front‑panel section on the extreme right‑hand side hosts another Distressor‑style rotary control to adjust the output level, along with a black rocker switch to power the unit on or off. Unity gain is achieved with the control set at 5.5, while the maximum (10) provides an extra 20dB of gain, and zero mutes the output — so full fades can be achieved, if desired.

In Use

Configuring the Mike‑E is very straightforward once you're familiar with the multi‑mode switching of some of the buttons, and the many LEDs give good status feedback. With the CompSat section bypassed, to assess the mic preamp, I was surprised at how clean and sweet it was with a range of capacitor mics. Having past experiences of the Distressor in mind, I was expecting a distinctly coloured sound, but actually the preamp provides a commendably quiet, neutral and detailed sound character. I found the unusually low input impedance (around 600‑800Ω) did influence the sound of some dynamic mics slightly, forcing the sound to close in slightly — but then most of my own preamps operate with abnormally high input impedances, and I guess I'm used to the sound that dynamic mics give in those circumstances. Backing the gain off to select line mode raises the input impedance to 3.3kΩ, which is still way below the normal 10kΩ of most standard line inputs, but shouldn't trouble any modern line‑level source.

Adjusting the gain is simple enough. The 5dB steps work well, and the digital control ensures that the settings are repeatable. The lack of a level meter isn't really a problem, as recorder, converter or DAW meters can be used easily enough. The high‑pass filter works at removing sub‑sonic rubbish, but manages to add a subtle but noticeably warming character in the process.

I'm not overly happy about phantom power appearing on the quarter‑inch input socket, and I'm very surprised that the phantom power isn't disabled when line input mode is selected. That should be trivially simple to achieve given the digital control paradigm used here — but this isn't the only product on the market to suffer that particular 'feature', and it just requires some care and thought when connecting line‑level sources. The DI input works as expected, and my concern that the input impedance appeared a little low was unfounded, because a range of guitars and basses sounded great through this unit. Again, with the CompSat section bypassed the DI input is essentially very clean and detailed, just like a decent DI box.

Switching on the CompSat section allows the Mike‑E to really display its versatile character. Leaving the compressor on a 1:1 setting so that only the saturation stage is working allowed a subtle richness to be added to the sound, building as the Drive control was advanced progressively into a much more grungy distortion — all very easily controlled and generally very musical. Bringing in the compressor section, the low 2:1 ratio caters for gentle and relatively transparent bus compression, while the 4:1 and 8:1 settings are obviously much harder and more aggressive — although the broad soft‑knee transfer characteristics make the transition from linear to compressed fairly gentle at all settings. The attack and release parameters work broadly as expected, although I suspect that some degree of programme‑related automatic variation is going on as well — and there's even a hidden configuration mode to make the side-chain more sensitive to high frequencies and transients. The Nuke mode is more or less a hard limiter, although a very good‑sounding one most of the time!

The really impressive aspect of this section is the very wide range of adjustability, and the tonal range that this allows. The Mike‑E can be used equally well on anything — vocals, guitars, basses, kick, snare, overheads or whatever — and a setting can be found very quickly and easily that complements the source tastefully or messes with it comprehensively, but in a creative and musically appealing way.


I can't think of any other preamp/compressor that has the same extraordinary level of flexibility, ease of operation and extreme tonal range. It does clean and bright, dark and fuzzy, and everything in between, and with only a couple of controls and switches, finding a sound is a very fast and intuitive process. It's an expensive preamp, but it is unique — and well worth an audition.  


There are loads of preamp/compressors around, but I really can't think of any quite as versatile as this.

Published February 2010

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