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DAV Electronics BG5

Recording Channel
Published August 2004
By Hugh Robjohns

DAV Electronics BG5Photo: Mark Ewing

This premium recording channel has a big Decca-pedigree sound which belies its unassuming 1U rackmount box.

I reviewed DAV Electronics' first product, the BG1 dual-channel mic preamp, back in SOS December 2003. Since then the range has expanded to include a quad preamp (BG2), a stereo mastering equaliser (BG3), and a stereo limiter (BG4). However, the subject of this review, the BG5, is a full recording channel that draws together various elements from each of its forebears, comprising as it does a mic preamp, a simple two-band equaliser, and a compressor/limiter. Mick Hinton, the designer, worked for many years for The Decca Recording Company, and all the BG products are designed in the Decca tradition — family traits include a recognisably 'big' sound quality, exemplary technical specifications, and precise control functions.

Number Five Is Alive!

The BG5's 1U rackmount box measures about 250mm from front to back, with a simple black paint job and an brushed steel lid. All of the rotary controls are switches, ensuring repeatability and accuracy of settings, and all the buttons have associated LEDs — which is just as well given that it would otherwise be hard to see the status of the black buttons on the black fascia! The rear panel carries a trio of XLR sockets for mic and line inputs, plus a line output. There is also a phono socket to link the compressor's side-chain to a second unit for stereo applications. The unit features an internal linear mains power supply, and the encapsulated toroidal transformer is mounted on the right-hand side, well away from the sensitive microphone circuitry. The front-panel controls are all well spaced, with white legends and markings which are easy to read. Some of the legends on the BG1 were in red and blue, which I found became unreadable in low-light conditions — but the all-white markings of the BG5 prevent such difficulties.

The front-end circuitry is essentially the same as in the BG1, based around an Analog Devices SSM2017 input device. Although this chip is widely used, the capabilities of ostensibly identical designs vary considerably according to the supporting components, PCB layouts, circuit topologies, and so on. Mick Hinton appears to have optimised his design very well, and the BG-series products undoubtedly offer one of the best incarnations of the SSM2017 front end I have heard.

The input gain is adjusted from 26dB to 59dB in 3dB steps, which means there's no practical need for a fine level trim control. A little more gain might be useful on occasion — especially if using low-output ribbon mics — but it shouldn't prove a problem in practice with modern mics. A quarter-inch socket by the gain control provides a high-impedance input for guitars and basses. The DI signal is handled by another Analog Devices op amp, this time the high-quality OP275 chip, which features a Butler front end — this is the name given to a special input circuit containing both bipolar and JFET transistors, the combination of which is supposed to combine the precision and low noise of bipolar devices with the speed and transient handling of JFETs. In fact, this chip is used throughout the BG5, including as the output driver, but it is relatively unusual because it is two or three times more expensive than the usual op amps which tend to be employed in most products of this kind — the TL072 or NE5534A, for example. The input selection is performed by a couple of sealed miniature relays, controlled from a front-panel button and the switching contacts on the DI input socket — the latter taking priority regardless of the mic/line switch setting.

Like its siblings, the BG5 doesn't have any level meters as such, but the internal headroom is indicated by three LEDs. Two green LEDs show signal levels at +8dBu and +18dBu. The third LED illuminates red when the signal reaches +21dBu, at which point the preamp still boasts an impressive 8dB of headroom. This factory-standard level calibration is designed to correspond to the alignment of most professional A-D converters, but it can be specified to conform to other operational levels, if required.

A row of six black buttons provide the usual range of input-conditioning facilities. These include 48V phantom power to the mic input, mic/line switching, 30dB input pad, input polarity reverse, 50Hz high-pass filter, and a bypass function for the equaliser circuit.

Signal Processing

The equaliser is a simple two-shelf affair derived from the BG3 mastering equaliser, and is located in the signal path before the dynamics processing; there is no facility to move it after the dynamics. The turnover of the low-frequency shelf can be switched in octave intervals between 50, 100, 200, 400, and 800Hz, and the associated gain control provides up to 7.5dB of cut or boost switched in 1.5dB steps. The high-frequency shelf turnover can be set at 1, 2, 4, 8, or 12kHz, and the available gain adjustment is the same as for the LF shelf.

The compressor/limiter, like that in the BG4, is apparently based on circuit designs used by Decca in the late '70s, famed for their very low distortion and low noise. In this version, a transconductance op amp is employed as the basis of a voltage-controlled amplifier. I found the dynamics section less than intuitive, partly because it has the most confusing labelling, and partly because no handbook was provided with the review unit. I was able to work the functionality out by experimentation, but it turned out not to be quite as I had anticipated from the panel markings.

The operational controls are separated from the equaliser controls by three more black buttons, again with associated red LEDs. The first is labelled Lim Out above the button, and In below it, and this switches the dynamics processing section into circuit. However, the make-up gain remains operational even if the dynamics processing is switched out, as does the gain-reduction meter. The second button is labelled Lim Off and initially I assumed this implied that the dynamics processing incorporated separate peak limiter and compressor elements. However, this is not the case — there is only one dynamics process here. What this button actually does is disable the VCA in some way to remove any gain reduction completely — it came as a surprise to me too! I found the facility useful when I didn't want to use the dynamics processing and was distracted by the gain-reduction meter's flickerings. However, had the circuitry been designed so that the dynamics side-chain was isolated when the dynamics processing was switched out of circuit, this extra button wouldn't have been necessary at all. The third button is labelled Lim above and Comp below, and this switches the dynamics processing between fixed limiter (about 10:1) and compressor (about 2:1) ratios. The compressor has a soft knee, which eases loud signals into relatively gentle compression and helps to keep things sounding pretty transparent.

The three rotary controls are very simple: Gain Make Up is available up to 16dB in 2dB increments; Recovery settings of 0.3s, 1s and 3s are provided; and the Threshold is adjustable from 0dBu to +20dBu in 2dB steps. An unusual feature here is that the first step is from 0dBu to +1dBu, with 2dB increments to +19dBu followed by a final position of +20dBu.

I have to say this caused me problems at first. Looking at the markings, I initially assumed the scale went from -20dBu to 0dBu — meaning that you would have to turn the control anti-clockwise to lower the threshold and thus increase the compression. In fact, the control is scaled +20dBu to 0dBu, and you have to turn it clockwise to lower the threshold and increase the compression. It's a mind-set thing, with some compressors adopting one approach and some the opposite, and once I had figured out just what was going on here I was fine with it. The gain-reduction meter comprises eight green LEDs, showing 1dB increments to 4dB gain reduction, and 2dB increments thereafter to 12dB.

DAV Electronics BG5Photo: Mark Ewing

BG5 In Action

Thanks to the simple controls, the BG5 is fast and easy to set up — at least, once you've fathomed out the panel markings! The headroom LEDs are adequate for setting an approximate mic gain, and in practice the meters on the recorder, A-D converter, or computer would probably be used for judging actual levels. After all, as with the BG1 preamp, there is such a lot of headroom here that the input gain is rather less critical than might be the case in lesser products.

An important point worth bearing in mind, though, is that, like the BG1, this product delivers substantial output levels, and there is no output attenuator, so this is not a product that can be partnered easily with most semi-pro equipment. Obviously, you could generate a smaller output signal by setting a lower input gain, but this approach would compromise the noise performance and could make it impossible to establish an appropriate dynamics threshold.

I found the equaliser to be surprisingly useful for gentle contouring of the sound, capable of adding a little extra warmth at the bottom and sparkle at the top. I also used it to tame the slightly hard-edged character of a capacitor mic on a small string section. The compressor is equally subtle and transparent, and although I'm not a fan of using compression while recording it could prove invaluable in a live concert situation on a vocal soloist's mic, for example. The fixed ratio of roughly 2:1 provides a useful degree of dynamic control without being heavy handed, and is a good compromise for 'serious music' applications. However, it really isn't the tool for the job if trying to create a classic rock-vocal sound. Also, the limiter isn't a brick-wall design — there is some overshoot — so it would be wise to allow a few decibels of headroom if the intention is to prevent A-D overloads.

Conclusions

Overall, the BG5 is an impressive-sounding product, with a slightly 'larger than life' kind of sound quality which generally flatters good musicians and fine acoustics. In a straight A/B comparison with my beloved GML preamps, the BG5 couldn't provide quite the same weight and solidity at the extreme bottom end, but otherwise gave little away. With such vast headroom and fast slew rates, the BG5 never sounds strained or harsh, and transients are captured with finesse and precision.

As a general rule, most 'serious music' engineers are reluctant to use much in the way of EQ and dynamics when recording (or mixing for that matter), but the tools provided in the BG5 are gentle and subtle, and can prove beneficial on occasion. It is handy that they are entirely bypassable too, although this becomes a very expensive single-channel preamp if used routinely in this way.

Despite its understated styling and presentation, this product is designed to provide high-quality, controllable sound without fuss. It reminds me of the BBC's own equipment designs, on which I cut my professional teeth all those years ago: nothing much to look at, but perfectly designed for the job in hand — the equipment, not my teeth!

The quality of the signal path and the components that populate it in the BG5 are beyond reproach, and the sonic benefits are clearly audible. However, at its current UK list price the BG5 faces some very stiff competition indeed from units such as the Amek Channel In A Box, the Focusrite ISA220 and ISA430, and the TL Audio VP1. These are all extremely competent and highly regarded products, and all are more flexible and offer more features.

Of course, it might be argued that the BG5 is aimed at a different sector of the market — the 'serious music' sector rather than rock & roll — and in many ways it is better suited to this market than any of the four boxes mentioned above. However, that is a pretty small proportion of the overall marketplace, and the DI input doesn't really sit too neatly in that scenario either. So compared to the BG1, which offered superb value for money when I reviewed it last year, the BG5 seems a little unfocussed and overpriced.

If you are looking for a very clean and neutral recording channel with simple but sublime EQ and an equally fuss-free compressor, then the BG5 should certainly be on your auditioning short list. Had it been priced below £1000 in the UK, it would have represented very good value too. As it is, the bells, whistles, and stylish front panels of similarly priced competitors will probably attract more sales.

Published August 2004