SPL combine their acclaimed headphone amps with monitor control facilities and USB audio interfacing.
There are currently several affordable but good‑quality standalone monitor controllers on the market, but two recent additions come from the German manufacturer SPL. Part of their Series One range, the Control One and the Marc One are almost identical but the Marc One also includes a USB connection and stereo A‑D/D‑A converters; lots of monitor controllers have a D‑A and often USB connectivity to allow playback from a computer, but unlike most the Marc One can also serve as a two‑way line‑level audio interface. Both units also boast a good headphone amplifier, and a streamlined implementation of the crossfeed facility found on SPL’s Phonitor.
Both are desktop units with a vertical control panel on the front, and most signal and power connections plug into the rear; the single headphone output is sensibly placed on the front. They measure 210 x 50 x 220 mm and weigh around 1.5kg, so stay put on the desk well. A supplied wall‑wart PSU accepts any mains voltage between 100 and 240 V AC, outputting 12V DC at 1.5A via a coaxial plug. This is a Class‑2 power supply: there’s no direct connection between the monitor controller’s chassis or audio grounds and the mains safety earth, so ground loops shouldn’t be a problem, even with unbalanced connections. Internal DC‑DC converters transmogrify the 12V supply into ±17V rails for the audio circuitry, for a decent headroom margin. The coaxial power inlet is not a locking type and there’s no cable retainer either, but the power plug did remain securely in position during a week’s use on my desktop.
The rear‑panel audio connections comprise two stereo analogue line inputs, two stereo speaker outputs (one with a Sub output), plus a stereo line output. The Marc One model supplements these facilities with a USB B‑socket for connection to a computer, tablet, or smartphone.
All‑analogue connections are via quarter‑inch TRS sockets, but not all offer balanced operation. Line Input 1 and Speaker Output A (plus the associated ‘sub’ output) are all balanced, while Line Input 2, Speaker Output B and the Line outputs are all unbalanced. SPL argue there are technical benefits in using unbalanced (ie. ground‑referenced) connections in applications like a monitor controller, and there is some validity in that in specific circumstances. Yet, it also increases the risk of introducing ground‑loop problems, and I wonder if some potential purchasers might be put off at the idea of connecting their balanced‑input monitors to the Control One’s unbalanced outputs. However, in practice, sources and speakers with balanced I/O can usually be connected to unbalanced equipment without problems. The rear panel’s labelling indicates the use of TS plugs for the unbalanced I/O but, sensibly, they are TRS types with the ring terminals linked internally to the sleeve terminals (rather than just left floating), so TRS cables can be used reliably.
Plugging into just the left input sockets of the Line 1 or 2 inputs provides a dual‑mono signal, thanks to some internal normalling between corresponding left and right sockets — a useful convenience should you need to monitor any mono sources.
A pair of recessed DIP switches is located near the power inlet. The first attenuates the signal level to the speaker outputs by 10dB, which is a helpful option if using high‑sensitivity (or consumer) monitor speakers. The second DIP switch serves no function on the Control One but on the Marc One it determines the A‑D’s input source, and thus the signal that’s sent to the computer over the USB connection. The default mode routes Line Input 1 to the A‑D but operating the DIP switch sends a mix of both Line inputs 1 and 2 so that either source can be captured into the computer. The A‑D converter has a fixed alignment of 0dBFS = +15dBu, the idea being to allow budget analogue equipment to operate at moderate levels without incurring unwanted analogue saturation, coloration or distortion, yet still achieve a digital full‑scale signal. I did question the lack of options here for users expecting to work with professional headroom margins but SPL suggested that wasn’t their main target audience for this particular product....