ART Tube PAC & Tube EQ

We test ART's two compact tube processors to see if they sound bigger than they look.

When ART first introduced their Vactrol‑based opto‑compressor a couple of years back, I was more than pleasantly surprised by its sound, so when they announced they were combining a simplified version of this compressor with one of their tube mic preamps, I was keen to try it. As fortune would have it, they also have the Tube EQ in the same series, which arrived at the same time, so I got to play with that as well.

Both devices come in a 1U‑high, half‑width format, and as their hybrid circuitry includes tubes, they don't inflict further wall‑wart PSUs on us, but are mains powered (hooray!). The casings are both tough and attractive, with nicely curved front panels, and the white‑on‑black legending is clear and easy to read.

Taking the Preamp/Compressor first, this combines a mic/line preamp with an opto‑compressor where each section includes its own ECC83/12AX7 tube. Input is via a balanced XLR for mic‑level signals or a high‑impedance input for line‑level or guitar signals. Switchable 48V phantom power is fitted, along with a 20dB gain boost stage and phase inversion (the latter following the compressor stage). Outputs are available on both unbalanced jack and balanced XLR, so the unit may be used either as a direct recording channel or patched via a console insert point. A small, but effective 4‑LED meter shows the degree of tube drive, with a similar meter directly below to show the amount of gain reduction taking place, up to a maximum indicated value of 12dB.

I don't think I've ever seen a simpler compressor section than this one — but don't let that put you off, as it actually sounds pretty good on most material. There's a variable threshold control and an overall output gain control for the unit, but other than that, there are just four buttons, if you include Bypass and the Phase Invert switch. Compression is of the soft‑knee type, with a choice of two ratio settings labelled Comp and Limit — Comp has a ratio of 2.3:1 and Limit 6:1. The attack time is fixed at around six milliseconds, and the release time may either be fast or programme‑dependent, again selectable via a switch.

As far as I can tell, this unit uses the same low‑voltage tube circuitry as its predecessors, so the overdrive characteristics may not sound exactly the same as a high‑voltage design. Nevertheless, this type of circuit can still sound good, and it helps keep the price down.

PAC Sound

The circuitry may use low tube voltages, but it still sounds impressively clean, providing you don't drive it too hard (some 'starved tube' circuits can sound rather soggy). Background noise level is reassuringly low; my Rode NT1 mic sounded very sweet indeed.

At the lower compressor settings, it's possible to knock 6dB or more off the dynamic range of the signal with very few audible signs of compression, but for a more overtly compressed sound, adjusting the threshold to give 12dB or more of gain reduction will do the trick. Conversely, the Limit setting (6:1 ratio) can be used to give a much more 'squashed' sound, but because of the soft‑knee compression curve, the less gain reduction you set, the less obviously compressed the sound seems. At quite high gain reduction settings, the Limit mode is pretty unsubtle, but still in a smooth and musical way.

Trying a guitar through the high‑impedance jack input provides a nice combination of DI and compression, again with minimal noise. The preset attack of the compressor works nicely with guitar to give the attack of the sound a little life, but it isn't so pronounced that it sounds unnatural on vocals.

While esoteric tube processors are nice for those who can afford them, ART provide a very valid 'halfway‑house' product that improves on the facilities found in a typical mid‑price mixing console, yet costs far less than the top‑end tube models from the big names.

Tube EQ

Packaged in the same case as the Preamp/Compressor, the Tube EQ has independent input and output level controls and a choice of balanced XLR or unbalanced jack connectors, but there's no mic preamp in this model. The front panel proclaims this a parametric equaliser, but it's not, as there are no Q (bandwidth) controls — it's actually a 4‑band EQ with two sweep mids and shelving high and low sections. The shelving frequencies can be switched from 40Hz/120Hz and 6kHz/18kHz respectively, but the mids have no Q adjustment, not even a two‑position switch setting.

Though they're not parametric, the mids do feature switchable frequency ranges as well as +/‑12dB of gain: Lo‑Mid goes from
20Hz to 200Hz with a 'x10' switch to take it up to 2kHz, whereas the Hi‑Mid starts at 200Hz and goes up to 2kHz with the 'x10' switch pushing it up to 20kHz. This leaves a useful amount of overlap between the ranges to ensure you can get at exactly the areas of the spectrum you want to. Both Mid controls use dual‑concentric pots and knobs to save panel space, while a single Bypass button takes the whole EQ out of circuit.

Tube Sound

It turns out that the Tube EQ is well‑behaved and reasonably sweet‑sounding, though it doesn't have the flexibility of a parametric equaliser, especially when you need to home in on a narrow part of the spectrum. Even so, it has a wider range — and is rather nicer‑sounding — than many console EQ sections. The switchable shelving filters add to the usefulness of this equaliser, and in many situations, the lack of fully parametric mids may not be that important, as the filter widths have been sensibly chosen.

Summary

Both these units are well built, affordable, and have a clean, professional sound augmented by just a little tube warmth. For me, the Preamp/Compressor is the most attractive, as it offers mic/line/instrument preamp facilties as well as its very smooth‑sounding compressor section. The Tube EQ also sounds very good, but the lack of true parametric operation or a mic amp makes it less of an all‑rounder. I suppose ART would like you to buy both and patch them together!

While esoteric tube processors are nice for those who can afford them, ART provide a very valid 'halfway‑house' product that improves on the facilities found in a typical mid‑price mixing console, yet costs far less than the top‑end tube models from the big names. There are already a number of worthy products in this area (both hybrid and all solid‑state), including the excellent Joemeek range and TL Audio's hybrid processors, so it pays to listen to a few different models before deciding which one suits you best. You may also be surprised at how little tonal difference there is between some of the solid‑state and hybrid tube models, so go by what your ears tell you, not just the spec sheet. Whatever you do though, don't leave these two new ART models off your shortlist!