What, you might ask, is a ‘Sound-Nicening Louderizer’? That, apparently, is a feature of the AudioControl Bijou 600 zone amplifier and DAC. It was printed right there on the carton in the feature list, between ‘Compact Size 1U, ½ Rack’ and ‘Designed and Assembled in the Pacific Northwest USA’. It seemed to be almost a parody of the meaningless performance features seemingly appended to all manner of equipment.

But I had dark suspicions that it was in fact serious. After all, who wouldn’t want the sound from their amplifier to be nice and loud? Why not include a loopy ‘feature’ to deliver just that?

And then I read the manual and got the joke. 95% serious and informative, it has scattered throughout light-hearted moments. It suggests that you use the volume control ‘wisely for the good of mankind, the neighbours, domestic harmony and bliss.’ And it notes that the manual itself ‘was written, designed, printed and carefully placed right side up into the box in the USA on a wet and rainy day by a team of music lovers dedicated to making good sound great.’

Phew! Perhaps I am too cynical for my own good.

What is it?

So, putting sound-nicening louderizers to one side, what we have here is a very compact, high performance zone amplifier. But a bit more than that for it is effectively an integrated amplifier with both an analogue preamplifier and a built-in digital to analogue converter.

The power amplifier section is stereo, capable of delivering 100W from each channel into 8Ω loads and 200W each into 4Ω. AudioControl doesn’t talk about their design, but those figures, the compact size of the unit, and the warning that the left and right negative speaker output connections must remain isolated from each other, strongly suggest some kind of digital or Class D amplifier.

If you need more power then you can purchase a second Bijou 600 and bridge each of them. In this mode each unit is good for 400W of mono power into 8Ω (that’s the minimum impedance permitted, as usual with bridging).

As for being compact, it is one half the standard rack-mount width. A ‘single’ rack mount kit adds a false facia to its side along with ears for rack mounting. A ‘double’ mount kit allows two units to be joined together side by side and have ears appended for fitting to a standard mount. There are also available brackets, a plate and a protective box for wall mounting, or attaching to the back of a TV.

The unit comes with a compact IR remote which allows input selection, volume control, muting, power on/standby, headphone output selection and control of something called ‘AccuBASS’, which I’ll get to later. There’s also a hard wired power switch on the rear of the unit.

Setting Up

Setting up the Bijou 600 turned out to be really easy, thanks to the wonderfully clear manual. As mentioned, it’s also somewhat amusing, but this does not detract from the clarity. There’s even a block diagram so that you can see in what order the various settings are applied to the signal.

Each of the two digital inputs has both an optical and a coaxial connection, only one of which should be used. There’s also a pair of RCA sockets for analogue input. Now here’s the thing, while the unit clearly performs the functions of an integrated amplifier, it can also act purely as a zone power amplifier, or as a mixture of the two. The key to this is the row of small dip switches. Three of these are volume defeat switches for those three inputs. That is, if you switch on the one for, say, the analogue audio input, then the volume control will no longer work for signals on that input. They’ll be delivered at full volume. You use this if you are using some other preamplifier as a front end. AudioControl specifically mentions Sonos systems, where you might want to use a Multiroom front-end. The same would go for equivalent components in a Heos system.

Also, when adding speakers for a Dolby Atmos system (no receiver I’ve yet seen supports a full 7.4 channels without the addition of at least two amp channels).

Bridging the output to turn the unit into a high powered mono amp is again just a matter of flipping a dip switch. And, of course, using the two marked speaker connections. And, of course, feeding the other channel, provided by the ‘bridge’ line level output, on to the other bridged amp.

Why not just feed left and right directly to the two bridged amps from the source? That would work with analogue inputs, but not with the digital inputs. With this system, one amp accepts the digital input, decodes it, separates out the two channels, amplifies one of them and hands the other on to the other amp.

Incidentally, there’s a kind of reverse pad on the analogue input: flip a dip switch called ‘High Gain’ and this bumps up the signal level by 10dB, to cater for devices with a very low output voltage.

In normal operation the unit switches on when it detects an incoming signal (this works with both analogue and digital signals), and switches off again after eight minutes of no signal. Another dip switch defeats this behaviour. You might employ this when using RS-232C control or the 12 volt trigger, or if simply prefer to manage things manually.

Finally, there are two filter switches: 80 hertz high pass and 80 hertz low pass. The first applies to the speaker outputs and the second to the mono subwoofer output. Most add-on subs will have their own filter so you probably won’t need the sub one. Still, nice to have it there. The high pass filter should increase the performance of smaller speakers used in conjunction with a sub. Both filters use an 18dB/Octave filter slope.

The speaker connection terminal block has holes around 2 by 2.5 mm for the cable and a screw to tighten a guillotine to lock in the wires. That allows decent, but not super-fat, audiophile cables to be employed.

Performance

Having only one of the units, I confined my use to conventional stereo mode, and for the most part I fed the unit a digital audio signal to one of the optical inputs. The unit happily supported PCM signals at 16 bits, 44.1 kHz, and 24 bits at both 96 and 192 kHz.

I ran a check on the headphone output at various digital audio resolutions to make sure the DAC wasn’t faking it (unlikely, since a Wolfson DAC is used). It turns that the Bijou provides true high definition digital audio, although with a rather gentler anti-aliasing filter than is the norm. Rather than stretching 44.1 kHz signals out to 20 kHz and then cutting them off hard, it rolls off gently to be down by 1dB at 20 kHz, with output descending rapidly beyond that. Output was down by 0.6dB at 20 hertz as well.

With 96 kHz sampling, the same top end behaviour was maintained, except that the gentle curve continued – down by 2dB at 30 kHz, 3.5dB at 40 kHz. Not surprisingly, this continues with 192 kHz signals, down by 5dB at 50 kHz, 7.2dB at 60 kHz, 10.5dB at 70 kHz.

This isn’t unexpected. In my experience most high quality DACs are -3dB at 50 kHz anyway.

The mute key is nicely implemented, ramping the volume down to zero, and back up again when pressed a second time, over a period of something like a second.

The headphone output sounded clean, and supported very high levels of output. Inserting a headphone plug does not cut out the main outputs. Indeed, it doesn’t work at all unless selected with the remote. This is intentional: it means that headphones – or a wireless headphone transmitter – can be left permanently wired in place without affecting normal performance.

As for the amplifier’s main function of driving loudspeakers, it proved to be clearly capable of excellent performance, driving both my normal eight ohm compacts and floorstanding four ohm towers to high levels, imposing no character of its own on the sound.

I find myself returning these days a fair bit to Air’s 10,000 Hz Legend, a largely electronic album with challenging bass and signal phasing. The Bijou 600 applied excellent control to the loudspeakers, holding them back from excessive fizz or uncontrolled excursion in the bass drivers, while shifting the sound through space – well beyond the confines of the conventional sound stage – as well as the best audiophile amplifier could manage.

On acoustic-style male and female vocals, the natural deliver was precise and convincing. While with classical music again the amp delivered the signal in the best possible way, free distortion and without imposing any character of its own on the sound.

Most of all, the sound levels available seemed quite out of proportion to the size of this tiny amplifier. I’ve heard performances from multi-thousand dollar amps weighing twenty kilograms that would be hard to distinguish from this.

Class D or not, the heat production by this amp is fairly modest. That said, it is small and consequently doesn’t have a large area from which to dissipate that heat, so it ended up quite warm to the touch after a couple of hours of loud music.

As for the AccuBASS control, this is a bass booster. You can set the level of boost separately for each of the inputs. In general I’d caution against using this kind of thing, but it could help deal with some installation speaker weaknesses.

Conclusion

In the US the price of the unit is around $US850. Whichever distributor picks it up with have to price it significantly higher than the current Australian dollar conversion rate (to cover warranty support and other overheads, and provide a buffer for further currency shifts). Given the flexibility and performance of the AudioControl Bijou 600, any reasonable price would seem fitting for the unit.