Aurora Audio Sidecar

By stripping this mixer down to the bare bones of preamp, EQ and stereo summing, Geoff Tanner shows us that less really can be more when it comes to quality vintage-style consoles.

Aurora Audio are the brain child of Geoff Tanner and Alan Dickson. Geoff is a British former Neve Special Projects Engineer and Alan a Hollywood studio owner. This American company grew originally from Phoenix Audio in the late 1990s and the name change occurred when the third founding member, David Langford, decided to retire. Today, Aurora manufacture a range of preamps, equalisers, compressors, routers and summing buses, all of which are based on Neve-esque discrete transistor, class-A circuitry. However, out of respect for former co-workers at Neve, none of the Aurora products are direct copies or clones.

Given that Aurora were already making a range of console building blocks as standalone outboard products, it was only a matter of time before some sort of mixing desk emerged, and now it's here: the Aurora Sidecar. The 'sidecar' term is generally used to mean a secondary 'console', used essentially to extend the channel count of a main console for tracking or mixdowns, and often to introduce different sound character options at the same time. I'm sure we've all resorted to wiring in a compact budget console when we've run out of channels on the main desk or interface at some time or another. At the opposite end of the scale, Abbey Road Studios famously have two original Beatles- and Pink Floyd-era EMI TG 12345 16-channel desks which are used regularly as sidecars! Bringing it back to Geoff Tanner's world, a very popular sidecar amongst high-end studios is the old Neve BCM10, which was originally designed as a compact broadcast desk in the early 1970s. Geoff has refurbished and modified many of these over the years, but BCM10s are almost impossible to find these days, so it's not surprising that more and more people have been asking Tanner to come up with an alternative.

Sidecar Profile

As you'd expect from a Neve-inspired design, the construction of the Sidecar is modular.

The Aurora Sidecar benefits from Tanner's fifty-year career in audio electronics design and production, mostly involving class-A circuitry, and it has an extremely simple signal path. It provides ten channels, plus a stereo mix bus, and is built like the proverbial tank — though there are a few more luxury touches than the average tank! The heavy-gauge steel frame has hand-worked wooden side-cheeks and a leather arm rest, and the individual plug-in channel modules are supported by steel guide rails and held in place with thumbscrews at the top and bottom of the module. Each module has a steel frame with a screening plate on the left-hand side, and all audio and power connections to the rest of the desk's circuitry is via a 15-way D-sub at the base of the module.

A heavy external linear power supply unit provides a single-sided 24V power rail for the audio electronics, plus 48V for phantom power, and connects via a four-pin XLR at the back of the desk chassis. There are warnings in the manual about keeping it well away from audio transformers in the desk or elsewhere to avoid magnetic coupling from the mains transformer.

As I'd anticipated, each channel strip follows the broad design approach of the classic Neve input modules, so the mic/line input is transformer-coupled (1.2kΩ input impedance) and the discrete class-A preamp provides up to 80dB of gain. A dedicated unbalanced instrument input is also provided on every channel, along with a bypassable four-band semi-parametric equaliser and separate high- and low-pass filters. A polarity inversion switch, bus routing with pan pot, channel mute, Penny & Giles fader and VU meter are also provided, but there's no insert point.

The stereo mix bus uses transformer summing and the mix bus outputs are also transformer-coupled, again with dedicated output VU metering. However, there are no mix-bus insert points or any kind of monitoring section. In total, there are 24 audio transformers within the Sidecar and input signals will always go through at least one transformer — potentially three — depending on the signal routing and connections.

Channel Strip Detail

The Sidecar's Neve heritage is evident not only in the circuit designs, but also in the styling of the various channel controls.

The Sidecar flaunts its Neve heritage by using the same style of control knobs and colours: there are lots of fluted knobs in maroons, blues and greys, with the familiar big red wing-knobs for preamp gains. The eleven-way channel gain switch spans -10 to +80 dB, in 10dB steps, and accommodates both line inputs and mic inputs via the single-channel input XLR on the rear panel. There's around 26dB of headroom if the gain structure is set correctly, and a red illuminated button activates +48V phantom power while a second (yellow) button flips the signal polarity.

The instrument input is via a quarter-inch TS socket mounted on the channel strip below the gain knob. It presents a 10MΩ input impedance, and plugging in automatically overrides the rear mic/line input. The channel VU meter is wired across the transformer-coupled direct-output XLR on the rear panel, and so reads the post-fader level through the channel strip. There's no PFL mode, so channel gain setting must be done with the fader open at its unity position, with the output level registering on the channel VU meter aligned for 0VU = +4dBu.

The semi-parametric, four-band equaliser is a typically comprehensive design, each band being individually bypassable. The controls are laid out in a traditional style, with separate high- and low-pass filters at the bottom of the section, along with illuminated buttons to engage the main EQ and each filter individually.

The EQ section gain knobs follow Neve's tradition by being coloured red and having centre detents at unity gain. The high and low shelf sections both have a three-position toggle switch above the gain control, which provides a bypass mode (in the centre), and alters the gain range at each end (±6dB or ±16dB). The high shelf has five selectable turnover frequencies spanning 3.3 to 15 kHz, while the low shelf five settings between 33 and 330 Hz — both set with grey rotary switches.

The high and low mid-band sections have larger knobs to set their centre frequencies, each providing ten settings from 2 to 12 kHz and 100 to 1400 Hz, respectively, plus individual bypass positions. More three-way toggle switches above their gain controls adjust the bandwidth (narrow, medium or wide), and up to ±20dB of gain is available. The 18dB/octave high-pass filter switch towards the bottom of the channel strip offers five turnover frequencies (from 22 to 270 Hz), while the low-pass filter offers five more options (between 3.9 and 18 kHz).

At the very bottom of the channel strip is a pair of mix bus routing buttons to send the channel output to the left or right mix bus. If both buttons are engaged a green status LED indicates that the pan pot is switched into the circuit path. An illuminated red button mutes the channel output from both the mix bus and direct output and the long-throw P&G channel fader is configured with 10dB of additional gain if fully open.

The stereo mix bus employs the traditional Neve resistive voltage summing configuration and unbalanced transformer coupling into the mix bus gain stage, (as opposed to the current summing technique associated with virtual-earth mix amps used in most modern consoles). The mix bus P&G faders are differentiated from the channels with red caps and unity gain at the fully open position. There are no other mix bus controls, and the mix bus VU meters are wired across the output XLRs (aligned to 0VU = +4dBu again).

Performance

Analogue connections are via the ubiquitous three-pin XLR connectors.

The Aurora Sidecar is, as you'd expect, all about sound character. In fact, it provides that in spades. It also won't surprise anyone that it's not the quietest or cleanest desk available on the market, and that's reflected honestly in the published technical specifications. For example, the signal-to-noise ratio is given as greater than -75dBu, giving a dynamic range of 101dB (most modern high-end consoles would achieve 10 to 20 dB more), and channel crosstalk is also surprisingly high, with a published figure of -70dB at 1kHz. (Crosstalk inherently gets worse at higher frequencies and most manufacturers quote the measurement for 10kHz). Distortion is better than 0.075 percent at 1kHz, again at least an order of magnitude 'worse' than most modern consoles.

However, these should not be considered to be bad specifications at all. The critically important point here is that the distortion sounds 'nice', the noise helps with integrating the mix, and the crosstalk helps to give the stereo image depth and stature. These aren't Aurora claims, by the way, they are my interpretation of why the Aurora Sidecar sounds the way it does and why so many of Aurora's clients want products like this.

There's a distinct sense of body and solidity to the overall sound of this sidecar and the mic preamp can be nicely overdriven to good effect, if appropriate (a major advantage of having a fader across the channel output). Transients are handled cleanly, but drums seem to gain an attractive weight and 'phatness' as they pass through the Aurora circuitry. Overall, the sound character seemed very evocative to me of the classic Neve 1081 input module, and of course the Sidecar reflects its feature set, too.

The channel strip is laid out with plenty of finger space around the controls, and the use of differently sized and shaped knobs and colour-coding makes navigation very easy. The controls also appear to be robust and of high quality, making the Sidecar satisfying to use, and it feels well worth its cost; this is a well-built professional product that should last a lifetime.

I've already highlighted the extremely simple signal path through the desk, and by connecting the channel-direct outputs to the studio console or a DAW interface, the desk essentially serves as the equivalent of a rack of Neve 1081s. However, it also enjoys the useful operational benefits of channel faders and individual VU meters to better manage the gain structure. Certainly, Geoff Tanner sees this as the normal way to work with the Aurora Sidecar when tracking. However, it does raise the question of how to track with compression (or other forms of signal processing), if that is the user's preference.

Obviously, channel-direct outputs could be routed to outboard compressors before sending their signals on to a recording console or DAW, but in this configuration the dynamics must always follow the channel EQ. The absence of pre-EQ channel insert points means that the only way to compress before equalisation is to route the outboard compressor's output back through a second channel strip (or daisy-chain an outboard EQ after the compressor) — possible, but probably not practical.

The same issue raises its head when using the Aurora Sidecar for mixdowns. Outboard dynamics can be patched in front of the channel line inputs, providing dynamics before EQ, but there's no easy way of reversing the order, if required, when using the Aurora Sidecar's mix bus.

Are these practical issues for potential owners? Some I discussed this with thought so, but Tanner thinks not, and he actually offers good reasons for not including insert points. For a start, he emphasises that this is intended as a sidecar, not a full console. The two products are each designed to be used in different ways. Also, he wanted to keep the signal path as short and clean as possible, while also controlling manufacturing costs, and I think that's all fair enough. At the end of the day, whether these potential signal-routing limitations are relevant can only be a personal decision. The Aurora Sidecar is what it is, and has no pretentions of being a fully equipped console. Moreover, not only does it lack insert points, but there are no auxiliary sends either and no monitoring section, so it couldn't really be pressed into service as a full console. It will always have to be used in conjunction with a full console or in a DAW-based rig with its own interfacing, aux routing and monitoring facilities.

Clearly, then, the Aurora Sidecar won't appeal to everyone, and it does take some effort to come to terms with the concept and application of a sidecar as opposed to a normal console. However, if viewed as a more flexible and satisfying variation on a rack of classic outboard preamp modules, its true value and appeal becomes obvious. Sound character and build quality are both excellent, the price seems fair, and the Aurora Sidecar is an impressive development from this interesting company. Just imagine what it would be like if Aurora were to build us a full console... Geoff?