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Buzz Audio ARC1.1

Recording Channel
Published March 2005
By Hugh Robjohns

Buzz Audio ARC1.1Photo: Mark Ewing

Buzz Audio have combined their top-flight preamplification and compression circuitry with a new equaliser design to create a versatile front end for recording.

The practical business of recording has evolved considerably over the century of its existence, partly because of technological advances and partly because of fashionable working practices. In the very early days, technical limitations meant that an entire orchestra or band had to be recorded acoustically through a single horn. Then came the electrical microphone, electronic amplifiers, and stereo recording, but the entire acoustic output of the musical ensemble was still recorded in one go. This approach continued through the 1950s, 1960s, and 1970s, using larger and larger mixing desks to balance the outputs of numerous microphones.

However, the introduction of multitrack recording changed all that, introducing the possibility of overdubbing. From the 1970s onwards it became increasingly the norm to record each section, or even each separate element of a production, individually. The obvious result is that it is no longer necessary (or fashionable) to record through a large mixing console — a single channel strip is all that is needed. To that end, stand-alone preamps, recording channels, and 'producer packs' have become increasingly popular. Fashion and convenience may have something to do with their popularity, but so too does the value for money they offer — big-console sound and flexibility on a modest budget.

One of the latest additions to this market sector is the new Buzz Audio ARC1.1 — a fully featured and unusually flexible solid-state recording channel boasting mic and line/DI input sections, a four-band EQ with separate high-pass filter, an optical compressor with separate FET peak limiter, and an output section with a switchable output transformer. Throw in multiple signal paths and comprehensive internal routing options, extremely high-quality audio circuitry, and Buzz Audio's attention to detail, and it quickly becomes obvious that the ARC1.1 is something rather special.

Buzz products have made several appearances in these pages, and elements from these individual signal processors have been combined in the ARC1.1. For example, the SOC1.1 stereo optical compressor was reviewed in SOS May 2002, with the MIA1.0 DI following in August and the MA2.2 mic preamp in December. All have impressed me with their sound quality, thanks mainly to the use of discrete Class-A circuitry and careful engineering design. As might be expected, such quality comes at a price, not least because the company is based in New Zealand, but for those whose budgets can stretch to such levels the sonic rewards easily justify the outlay.


The ARC1.1 is housed in a black-painted 2U rackmount enclosure which extends 300mm behind the rack ears. The front panel looks initially to be borrowed from the Apollo space ships — a nightmare of identical knobs and toggle switches! There are far more than on most recording channels, so this is a toy for serious 'tech heads'. Fortunately, the panel ergonomics and labelling make the actual operation quite straightforward, although it is necessary to get to grips with the concepts behind the sophisticated internal routing.

As always, the best place to start is the rear panel, and here we are faced with nine XLRs, a couple of TRS sockets, and an IEC mains inlet. The mains voltage is switchable for 230V or 115V operation, and a rocker switch allows the signal earth to be floated from the chassis earth if required. The top row of XLRs provides a balanced mic input along with a dedicated mic preamp output, plus a balanced line input and direct loop-through socket. The lower row of XLRs provides direct access to the inputs and outputs of the EQ and compressor stages — all fully balanced — plus the unit's main balanced output. Two TRS sockets provide a compressor link buss for coupling two ARC1.1s for stereo operation, and there's also an unbalanced side-chain insert point to the compressor.

That is an unusual amount of connectivity for a product of this type, and the reason for it is that each section (mic preamp, line input, EQ, and compressor) can be used independently on different signals, all at the same time! To make this possible, the ARC1.1 has four separate signal paths routed through a matrix of twenty-two relays, with oxygen-free cable linking the various circuit sections and relays rather than long and convoluted PCB tracks.

There is a main signal path (accessed via the various 'In' routing switches) running through the unit in the conventional way, culminating in the main output. In addition, each section of the equaliser and compressor can be removed from the main signal path and allocated instead to the corresponding external connection loops (via the Ext switches). Furthermore, each equaliser section can also be routed instead to the side-chain of the compressor. The reason for all those toggle switches will have now become clear!

Buzz Audio ARC1.1Photo: Mark Ewing

Mic & Line/Instrument Inputs

The control panel is divided into separate control sections with blue graphics, and each control is clearly identified with white legends. There is plenty of space around all the knobs and switches, so operation is very easy, and although there are very few LED indicators, the use of toggle switches makes the current status of each function fairly visible, even in low-light situations.

There are two discrete preamp sections, one for the microphone input and one for a line/instrument input. The mic section features two rotary controls and two toggle switches. Gain is continuously adjustable from 9dB to 50dB, and the knob has a light detented feel to it. One of the toggle switches increases the range by 15dB (24-65dB), while the second activates phantom power. There is no warning LED associated with the phantom-power switch, although a soft-start/stop circuit is claimed to minimise thumps and bangs A manual mute facility is also provided in the output section (see below) so that the output can be silenced when switching phantom power on and off, protecting delicate monitoring systems — and your ears!

The second knob is unusual in that it provides continuous adjustment of the input impedance, spanning 220Ω to 5.5kΩ. Most preamps that offer variable input impedance only allow a few switched settings, and rarely over such a wide range as this. The preamp is based on the proprietary BE40 discrete Class-A modules used in the SSA1.1 and MA2.2, which boast impressively low noise and fast transient capability.

The line input section sits to the right of the mic input, sharing a similar panel layout. The top rotary control adjusts the gain from 0dB to 40dB with the same light detented control action, and a toggle switch allows this range to be reduced by 10dB to span -10dB to +30dB. Not only is this a more practical range for many applications, but when selected it also increases the input impedance from 20kΩ to 70kΩ, which may have sonic benefits if you're receiving signal from some line-level devices with weedy output stages.

In place of the impedance control of the mic preamp section is an unbalanced quarter-inch socket optimised to act as a direct input for guitars. The input impedance is 1MΩ, and the second toggle switch activates this input in place of the rear-panel balanced input. The -10dB toggle is disabled when the unbalanced input is in use.

Output Stage

At this point, the logic of the signal path is broken, because the next panel section is the output stage. The top row of controls features a toggle switch to select the input source — the mic or line preamps — and a continuously variable output level control, This control is configured like a fader, with +10dB of gain available above the nominal zero level, and it reduces the signal all the way down to silence if rotated fully anticlockwise.

The lower row of controls comprises three toggle switches, the first being a three-position type providing normal, mute, and phase-reverse functions. The Normal switch position maintains absolute phase through the unit, meaning that a positive voltage from the microphone generates a positive voltage at the output of the unit. The middle toggle switch allows the compressor side-chain to be monitored in place of the main output, which is useful for setting up an equaliser to provide frequency-conscious compression, for example.

The third switch is very interesting, as this routes the output through a special transformer designed specifically to introduce some distortion and 'colour' to the sound. Below 0dBu, the transformer introduces around 0.5 percent distortion at 50Hz, helping to add a slight thickening effect to the sound. By driving the levels harder, the transformer can be coaxed into saturation, increasing distortion levels to about two percent. A useful characteristic of transformer distortion is that the amount of distortion decreases with increasing frequency, so that above 1kHz the distortion is below 0.1 percent, even when driven very hard. This helps prevent the top end becoming harsh and glassy — the benefits are very much restricted to a thickening of the lower mid-range and the low frequencies, which is just where they are needed!

At the right-hand side of the panel are two vertical bar-graph meters. One shows the compressor gain reduction, while the other can be switched with yet another toggle switch to show either the input level (after the mic/line preamps) or the output level (after the output level control), or it can be turned off altogether. The meter is a peak-reading type with a slowish decay time, and is scaled from -32dBu to +18dBu. A separate Over LED provides a clip warning when the signal exceeds +20dBu. The circuitry driving this indicator monitors the signal path at several key points, and continues to monitor the compressor and EQ even if they are switched to the external loops. It also remains active even if the main peak meter is switched off.

Four-band Equaliser

The equaliser is very highly specified, with two parametric mid-frequency bands, high- and low-shelf sections, and a separate high-pass filter. Each of these can be switched independently between the main internal signal path, the compressor side-chain, or the rear-panel input/output loop, where it can be used to process an external signal. Unusually, there is no facility to bypass the EQ section as a whole, so checking whether your tweaking has really improved the situation (as opposed to just making it louder and brighter!) is impossible. The closest you can get to bypassing the EQ is to switch each separate stage to either the external or side-chain paths, which may be less than desirable, of course. This omission is one of the few disappointments of the ARC1.1. The handbook recommends switching unused EQ sections (after setting their cut/boost controls to zero) into the compressor side-chain, thereby removing them from the audio signal path entirely.

The first component of the EQ is the high-pass filter, the controls of which lie below the output section on the front panel. A three-way toggle switch sets the routing, while a rotary control provides continuous frequency adjustment from 25Hz to 450Hz. The filter has a 12dB/octave slope. The next portion of the front panel is occupied with the fixed-frequency high- and low-shelf sections. These both have continuous cut/boost controls which span ±17dB (with a centre detent at 0dB), and the obligatory routing switches. In addition, two more toggle switches allow the low-shelf turnover to be lowered from 120Hz to 60Hz, and the Q of the high shelf to be increased — the Broad position provides a response that resembles most high-frequency shelving equalisers, while the Tight setting provides a much steeper slope, allowing the high shelf to operate more like an 'Air' control. Apparently, the low-shelf section employs a proper choke inductor (rather than an electronic gyrator circuit), and this is claimed to provide a much tighter bass than would otherwise be possible.

The two parametric mid-sections are identical save for their overlapping frequency ranges. The first spans 30-700Hz, while the second covers 160Hz-3.4kHz. Both have continuous cut/boost controls offering a range of ±15dB (with centre detents at zero); both have routing switches; both have continuously variable Q controls; and both have x10 frequency-multiplier switches. In both cases the filter bandwidth can be varied from a narrow 0.25 octaves (Q value of 4.0) to a broad 1.7 octaves (Q value of 0.6).

The frequency-multiplier switches afford these EQ sections an enormous range, but without sacrificing control accuracy. So the first mid-section can be switched to cover 0.3-7kHz and the second to 1.6-34kHz! The handbook explains that the circuit topology is based on a constant-amplitude phase-shift network (as opposed to the more common state-variable filter), an idea first promoted back in the 1980s by well-known console designer Steve Dove, who worked with Ted Fletcher at the time.

Buzz Audio ARC1.1Photo: Mark Ewing

Compressor & Limiter

The compressor section combines an optical compressor with a solid-state (FET-based) peak limiter. The signal-routing options for the compressor and limiter differ from those of the equaliser. The limiter can be switched into the main signal path, into the external compressor loop, or completely out of circuit. The opto-compressor can be switched to the external loop or the main signal path. In the case of the latter, it can be switched before or after the EQ section. Note that it is impossible to bypass the compressor completely — you can only move it between the main and external signal paths. While the latter may serve as a bypass function if the external loop is not being used, the reverse situation is unlikely to be acceptable.

The compressor itself has a simple set of variable rotary controls comprising Drive, Ratio, Release, and Make Up. The Drive control effectively sets the threshold, but is scaled simply from one to 11 — bigger numbers mean more gain reduction. The Ratio control is one of only two rotary switches on the unit, offering ratios of 2:1, 5:1, 10:1, and 20:1. The opto-compressor has a gentle soft-knee characteristic.

The second rotary switch provides a selection of five release times plus an automatic option. Strangely, the control is calibrated 1, 2, 4, 8, and 16, but these values actually refer to 0.1, 0.2, 0.4, 0.8, and 1.6 seconds of recovery time from 20dB of gain reduction. The automatic option provides the usual characteristics — fast recovery from loud transients with a slower recovery for more continuous signals. The attack time can also be adjusted via a toggle switch, the options being fast (1ms), slow (70ms), or automatic (programme-dependent). A third toggle switch activates the stereo link buss via the rear-panel quarter-inch socket mentioned earlier.

The Compression Make Up control provides up to 15dB of gain to restore peak levels after compression. A vertical bar-graph meter shows the gain reduction from 1dB to 26dB, and its illumination accurately reflects the attack and release time constants in action, providing far better visual feedback of the dynamic changes than a simple VU meter ever could.

The limiter is equipped with a continuously variable threshold control (ranging from 0dBu to +20dBu) and two toggle switches. The first adjusts the release time between Fast (0.1 seconds), Medium (0.75 seconds) and Slow (2 seconds), while the second routes the limiter section between the main internal path and the external compressor loop, or puts it out of circuit altogether. The limiter has an infinite ratio and is always placed as the final processor in whichever signal path it is inserted into — immediately prior to the output level control when in the main signal path, and after the opto-compressor to ensure fast transients that might escape the compressor are caught. An LED illuminates whenever the limiter is triggered into applying gain reduction. The limiter uses a special kind of FET which is optimised to work as a variable resistor (rather than as a switch or amplifier), and the circuit topology combines both feedforward and feedback paths to ensure very fast and accurate reactions to transient signals.

The Bee's Knees

The ARC1.1 has a sound quality to match its price — it sounds expansive and slightly larger than life, with plenty of air at the high end and a weighty, solid bottom end. The specifications claim a bandwidth from 4Hz to 400kHz (-3dB) and I can easily believe it. The EIN figure for the mic input is -132.5dBA and the distortion is better than 0.001 percent under most circumstances.

As a stand-alone recording channel, I found the ARC1.1 to be a very impressive tool. Using just the mic preamp through to the main output, I found it handled dynamics very well, with a fast, detailed sound. It exhibited a fundamentally neutral character and an open, airy quality. Switching in the output transformer added a distinct richness to the lower mid-range and bottom end, making the source sound slightly thicker and more dense, but without any unpleasant harshness. As expected, pushing the levels harder decreased the subtlety of the effect, but it never became unpleasant.

Introducing the equaliser had a negligible effect on the signal quality, and the facilities allowed a wide range of tonal shaping and correction to be applied quickly and easily. The lack of an overall bypass facility was frustrating, but individual sections can be bypassed easily enough if the external loop isn't being used. The frequency and bandwidth ranges of the two mid-sections proved to be well chosen, and the ability to 'stiffen' the high shelf was also useful for adding a little sparkle without harshness.

The opto-compressor seems to share similar characteristics to the SOC1.1 — if my notes from that review are to be believed — which is not surprising given that the control functions (and, I suspect, the circuitry) are identical. Overall, the compressor was equally at home whether used for some gentle taming or full heavy compression. It doesn't always sound 'transparent', in that you are aware of it working at times, but its contribution always seemed appropriate and musical, and it is easy to set up and adjust. The gain-reduction meter is particularly instructive when adjusting the Drive and Release controls, and the peak limiter very effective at catching transients that the slow optical compressor couldn't hope to deal with.

The ARC1.1 is certainly a very versatile unit, although I'm not convinced that such flexibility is necessary, and some key features have been sacrificed along the way. Nevertheless, it maintains the sonic standards set by its siblings and is a worthy addition to the upper echelons of the recording-channel market.

Published March 2005