SPL Channel One Mk3

With a Transient Designer, a de‑esser and an unusually versatile input section, there’s more to SPL’s recording channel than most.

Sound Performance Lab (SPL) have been making high‑quality audio gear since 1983. They first made a name for themselves with their Vitalizer, but it’s probably their next innovation, the Transient Designer — the first dynamics processor that didn’t rely for detection on the input signal crossing a level threshold — for which they’re now best known. Now, SPL’s pro audio range includes everything from preamps, channel strips, audio interfaces and mixing desks to mastering gear, monitor controllers and high‑quality headphone amps, and with the last of those they also cater for the hi‑fi market.

For review here is the third iteration of their Channel One. Like its predecessors, this analogue recording channel comes in a vented 2U 19‑inch rackmount chassis, but while it borrows plenty from the Mk2 version, this is a significant redesign that goes much deeper than the darker and, to my eye anyway, more impressive and easier to read front panel. The most notable changes to the feature set include a revamped preamp section, and this is now joined by a dedicated valve‑based saturation processor. The MkII’s headphone monitoring facilities have been dropped too and although this was a high‑quality feature, it’s one that I suspect many users will have found superfluous. More than compensating for that is the inclusion of a Transient Designer, which should increase this device’s appeal and versatility significantly. The de‑esser, EQ and compressor sections seem largely unchanged, but the metering has been rethought: the previous version had LED meters for gain reduction and output level, whereas we now have a large moving‑coil meter that can be switched to show gain reduction, input level or output level. A switch sets this meter’s 0VU position to correspond to output levels of +6, +12 or +18 dBu (that’s the only means of user calibration). What’s less obvious from the pictures is that SPL have opted for beefier power rails (±18V), and that the build quality on the inside is impeccable, with traditional through‑hole components used throughout.

Ins, Outs & Amplification

At the start of every channel strip comes the preamp, and this one is more versatile than most. There are actually two versions of this device: the regular one is electronically balanced, while the presence of Lundahl input and output transformers differentiate the Channel One Mk3 Premium. The mic amp is a discrete solid‑date design, but it’s joined by a separate valve saturation processor. So, between the main gain control knob (9‑68 dB for the mic inputs, and continuously variable) and the Saturation knob (turning this first switches in this circuit, then over 30 detented positions take you up to 100%), you can already access a range of sonic characters.

There’s particularly generous flexibility when it comes to the inputs. On the back are two separate mic inputs (unusual for a mono device), and a dedicated line input, all on XLRs, while on the front there’s a high‑impedance TS instrument input, which takes precedence over the line input when a jack is inserted. A toggle switch selects the source (Mic A, Mic B, Line/Inst), while separate switches for each mic input engage +48V phantom power. Three more switches operate a 20dB pad, a polarity inverter and a fixed 80Hz 6dB/oct high‑pass filter. Though not indicated (that would have made the panel crowded) the gain range for line signals is ‑20 to +16 dB, and for instruments ‑6 to +30 dB. And if you have the input transformer option that adds a chunky 14dB to the values on the scale....