Gainlab Audio GLA-MP1 Bishop

Gainlab’s channel strip delivers high‑quality valvetube preamplification and optical compression, along with some interesting tone‑shaping options.

We’ve looked at a couple of Gainlab’s products in the pages of SOS already. The Dictator variable‑mu compressor (SOS December 2021) and the Empress equaliser (SOS April 2022) both impressed us with their combination of good build quality, great sound and value for money. So when I was offered the opportunity to test their Bishop Channel, a recording channel strip, I was keen — and I wasn’t disappointed.

Controls Overview

The first stage in the signal path is a valve mic/line/instrument preamplifier. Its large, stepped gain knob is surrounded by a busy‑looking legend, with two concentric circles; each one indicates the setting for a different gain mode, with the modes selectable using an adjacent metal toggle switch. In the low‑gain mode, this stage can apply up to 40dB boost, while in high‑gain mode it can add up to 60dB. All this is achieved using three vacuum tubes. A neat yellow lighting system clearly indicates which mode you’re in, with two backlit circles around the legends as well as the switch LED lighting up to give you that confirmation, meaning you don’t have to squint to see how the toggle is set: a pleasing combination of style and substance!

There are seven metal toggle switches nearby, most relating to the preamp. Three are for features you’d expect on any modern preamp: 48V phantom power, a pad (for the mic input only) and polarity inversion. There’s also a power on‑off switch for the whole unit, a selector switch for mic, line or instrument mode, and another to choose between a front‑panel input and one on the rear. A dedicated saturation stage for the instrument input allows you to add some colour to clean DI signals using a smaller Drive knob that’s placed top left of the main gain control. As well as allowing deliberate coloration of the sound, this can be really helpful when used more subtly to tame any spikiness in a guitar signal before it hits the valve stages. I was a little surprised to find on some online images that the front‑panel input appeared to be an XLR, rather than a combi type into which you could plug a bass or electric guitar directly... but fear not! That must be an early version, since the review unit featured just such a combi. (It’s perhaps worth noting that, when active, phantom power is present on the XLR whether you have the mic, line or instrument setting selected.)

This is an optical compressor that, I think, is broadly based on the Teletronix LA‑2A design, but it’s not a direct clone and is actually more sophisticated.

To the right of the gain knob and in the centre of the 2U rackmountable unit is a large backlit moving‑coil VU meter that displays the output level. A recessed preset allows you to calibrate the meter’s zero point with a small screwdriver or similar, and next up we have the compressor stage, with its own LED metering. This is an optical compressor that, I think, is broadly based on the Teletronix LA‑2A design, but it’s not a direct clone and is actually more sophisticated. While it’s a single compressor (there’s only one optical cell) there are, as Gainlab put it, two slopes at play. Each has its own threshold control and independent 11‑LED gain reduction meter. The top 10 LEDs indicate 1dB of gain reduction each, so the meter has plenty of resolution in the most useful range (if you’re crushing a signal by more than 10dB, who cares what the meter says?). Beneath the Threshold controls are chickenhead knobs for Character (a knee control, I think) and Time Constant. As on most compressors of this type, there aren’t separate attack and release controls but there are five switched attack‑plus‑release settings, ranging from Slowest to Fastest, plus a sixth, programme‑dependent position.

The last knob, an output attenuator, has Off, ‑3, ‑6, ‑8 ‑10 and ‑12 dB settings, so you can bring down the output while increasing the gain or backing off the compression, allowing you to maintain sensible signal levels and judge changes in tonality without loudness really coming into play. (There certainly can be changes in tonality if you drive the input stage, even before you bring the compressor into the equation.)

Above this knob is a toggle switch to (dis)engage a high‑pass filter, with Off in the centre position, a 60Hz filter below and a 120Hz filter above. So there’s scope to tackle unwanted LF rumbles on their own, or to counter any unwanted proximity‑effect bass lift. Finally, we come to the Bishop’s secret weapon: another tiny toggle at the top right that engages a dynamic air‑band boost at either 20 or 30 kHz.

Around the back, there are separate XLR inputs for mic and line sources, meaning you could for instance have the mic input hooked up to a wallbox in the live room, the line input hooked up to your patchbay, and still have the front‑panel input available for mics and instruments. The front‑ and rear‑panel mic sockets are wired in parallel but switched automatically, with the front‑panel XLR taking precedence when a cable is plugged into it (plugging an instrument into the centre jack won’t break the connection to the rear mic XLR, though). Also on the rear are an output XLR — Gainlab quote an output impedance of 150Ω — a ground‑lift toggle switch, and an IEC mains power inlet with built‑in switch and fusebox.

The Bishop offers separate inputs on the rear for mic and line sources, which will make integrating it into a patchbay trivially easy.

In Use

So, that’s the quick tour completed, but the all‑important questions are how the Bishop sounds and how easy it is to coax the desired sound out of it — and the headline response is that it sounds superb and it’s easy to use!

The valve preamp has plenty of range, and when applying the amounts of gain you’d typically want in a studio session for normal mic and DI applications, there’s impressively little by way of noise and distortion. The frequency response seems pretty much flat, too, but there’s definitely character available here if you crank the gain and pull down the output. It’s a character that, as with all the best tube gear, isn’t what I’d call ‘warm’ exactly (one man’s warm is another man’s ‘mush’!) but more in the ‘lively’ and ‘classy’ ball park, with a slight rounding of transients and a little pleasing ‘flair’ to the high end. It’s not dissimilar to the sort of thing I’ve heard when testing, say, Thermionic Culture or Manley gear, and not something that’s ever likely to disappoint. This is a characterisation that applies especially to vocals, which always came out sounding wonderful.

The instrument input isn’t unpleasant either. The discrete Drive circuit can add some really pleasing colour, although it’s worth noting that for instruments with passive pickups that happen to need bags of gain, I found it hard to get a truly clean sound without really cranking the tube Gain stage — and that, at the sort of levels I sometimes needed, this meant there a fair bit of hiss was audible. It’s not a problem as such, as it’s very easy to roll off the top end of a DI’d guitar or bass part before feeding the signal to, say, an amp simulator. Nonetheless, it would have been nice to either have more clean gain available on the instrument input, or perhaps a switchable low‑pass filter (maybe as another setting on the Dyn Air knob) to counter such boosted hiss.

While they might look complicated, the compressor controls are intuitive enough that you can find your way around and set up a pleasing sound without thinking too hard.

The compressor has that forgiving personality that should be familiar to anyone who’s used something like an LA‑2A or LA‑3A: somewhat relaxed and very easy to set up. Even though those dual slope controls might look complicated, they’re actually intuitive enough that you can find your way around and set up a pleasing sound without thinking too hard about it; it’s really just a case of setting the threshold for the desired gain reduction and then twisting the second slope knob to see what more it brings to the party — and it’s a useful way to shape the sound. You can use this compressor for graceful control of vocals, guitars and basses, or anything else you might usually use an opto compressor for. If you wish, you can really slam your drum room mic too, and I really enjoyed doing this on a parallel setup, where I could use the valve stages to add a bit of grit before clamping down on the transients and bringing up the drum sustains. Of course, you’d need two units for stereo... Similarly, I loved using the Bishop as a parallel distortion effect on vocals, though note that, as there’s no wet/dry blend on board, you’d have to set that up separately. Still, while this might have been a nice addition, I usually prefer to EQ the parallel path anyway.

The air band and high‑pass filter are worth a few words, since the numbers on the faceplate don’t tell the whole story. For example, the HPF’s 60Hz setting rolls off fairly gently, starting in the low hundreds and down by about 7.5dB by the time you get to 100Hz. So it’s definitely an audible effect, not just a rumble filter. The same goes for the 120Hz setting, which rolls down from about unity at 2kHz to ‑10 around 250Hz. Similarly, the air band’s frequencies might seem very high on paper, but the curves reach well into the audible spectrum. It’s nice that this band is dynamic, too, since it avoids raising things like tape hiss and the noise floor of analogue electronics when there’s no signal present.

Verdict

There’s plenty of competition when it comes to valve optical compressors, but this isn’t the most expensive option out there, and I reckon it’s better than anything else I’ve used at its price. The sound is everything I’d want of a tube preamp and, with the dynamic air band, more besides. With mic, line and instrument inputs, as well as front‑panel access for mics and guitars, it could work nicely in any studio, whether a musician/songwriter’s small home studio set-up or a pro studio’s rack. It’s packed with more facilities than its closest competition, and while that does make the striking front panel appear a touch busier than most, it’s far easier to use than it might appear. In short: highly recommended!