ART Pro Audio Solo MPA & Solo VLA

Both of these devices are part of ART’s new ‘multivoice’ series, which aims to provide a wide range of tonal options.

Over the years, ART (Applied Research and Technology) Pro Audio have been one of the more prolific manufacturers of valve‑based equipment for home and project studios. The arrival of their new ‘multivoice’ products, the Solo MPA (a hybrid microphone and instrument preamplifier that offers solid‑state and valve amplification) and Solo VLA (which offers a choice of optical compressor with a valve stage or a FET compressor), takes ART’s lifetime total of valve‑equipped products to a very commendable 24! They’ve always offered decent bang for buck, and I hope there’ll be many more to come. Below, I’ll cover the functionality of each of these two new products in turn, before explaining how they performed for me during the few weeks I had them in for review.

MPA Preamp

Arguably, it’s quite hard for anything to make the front panel of a mono mic/instrument preamp in a black 1U enclosure intriguing! However, the legends above and around the Solo MPA’s control knobs somehow manage that trick very well. Balanced, rear‑panel XLR and TRS jack inputs accept mic and line‑level signals, while an unbalanced front‑panel TS jack provides the high‑impedance (>800kΩ) instrument input. The first thing to catch my eye was the gain control: scaled from 0 to 40 dB, this sets the gain of the separate FET‑based preamplifier stages and it’s an unusual gain range on the face of it. But it can be augmented with two other stages: first, there’s a +20dB gain switch; and, second, you can apply up to 15dB of gain at the master output. So you have a generous total available gain of up to +75dB. This unusual arrangement appears to me to be designed to give the Solo MPA the ability to accept either mic‑ or line‑level signals.

As with the Solo VLA, the Solo MPA’s I/O are paralleled on XLRs and quarter‑inch jacks, and can be set to operate at +4dBu or ‑10dBV.

The Solo MPA’s wide‑ranging impedance control can coax different characters from some mics.Next to the gain knob sits a variable input impedance control for the microphone input’s FET preamp. This ranges from 600Ω to a whopping 80kΩ — that’s by far the highest input impedance I’ve seen on a general‑purpose mic preamp. As Hugh Robjohns explained back in SOS September 2023 (https://sosm.ag/qa-mic-preamp-impedance), lowering the input impedance of a mic preamp will significantly reduce a microphone’s output signal. This requires higher preamp gain to obtain a usable output level, which in turn leads to an increase in noise, and maybe also in distortion. The tonal effects of lower input impedances can include: high‑frequency roll off; changes in the mic’s response to fast transients; a reduction in dynamic range; and an increased prominence in the low to low‑mid frequencies. All of which can lead to a subjectively ‘thicker’ overall sound. Increasing the input impedance, on the other hand, will not only lead to an increase in the level of the mic’s output signal, but will also tend to improve the mic’s dynamic range and linearise its response at low, low‑mid and high frequencies.

Whether or not these effects are desirable — or even audible — will depend both on the individual microphone concerned, and on the source being recorded. Dynamic (including ribbon) mics and older transformer‑equipped capacitor mics are usually more responsive to changes in preamp input impedance, because their output...