New Classé Sigma SSP processor, launched with two matching power amps, plays it simple in the quest for ultimate sound quality

Interesting afternoon at the London Bowers & Wilkins office yesterday, hearing about – and hearing – the new Classé Sigma series with company CEO Dave Nauber.

The range is designed to slot in below the existing Classé Delta models, but above home cinema electronics from mainstream manufacturers: it has been built with performance very much in mind, and to be as capable when used in two-channel mode as it is in 5.1- or 7.1-channel working. And to that end, the £4250 Sigma SSP processor/preamplifier at the heart of the system is as remarkable for what it doesn’t have as it is for what it does.

Nauber points out that most AV processors and high-end receivers are over-complex, and have a stack of facilities most users will never explore. While agreeing with my point that this is symptomatic of the features arms-race between manufacturers, he noted that many of the sockets on the back of such products will never be used.

For example, how many analogue video sources do you now have in your system? Are you really still running a VCR through your AV system? No, thought not – which is why the Classé Sigma SSP has done away with all those composite and component sockets, and concentrates on HDMI video and audio. As Nauber says, if a buyer really wants to connect an analogue video source, there’s no shortage of third-party add-ons available to do the conversion.

Similarly, the Sigma SSP is light on analogue audio inputs for the same reason, having just three sets – one on XLRs, and two on RCA phonos, with the option of a phono module fitted internally if required.

What it does have is a good range of digital audio connections, with three coaxial, two optical, asynchronous USB on the rear panel for computers, a re-clocked asynchronous USB on the front panel for iOS devices and the like, Ethernet for DLNA streaming and AirPlay.

There’s also full digital bass management, nine-band parametric equalisation, and of course eight channel output for the connection of power amps. Interestingly, a balanced option is only provided for two channels, Nauber pointing out that it made more sense to go for a high-quality balanced option for the stereo channels rather than attempt to do so on all channels, which would entail the use of less expensive balanced sections – or of course a substantial price hike!

The SSP is also built with modular audio DSP and video boards, so that features such as Dolby Atmos/Auro 3D sound and 4K video can be accommodated once sufficient software is available and standards are set, Nauber pointing out that current products with 4K video handling may not be compatible with final 4K standards in a couple of years time. As he says, the company could have built in 4K handling sufficient to handle future standards, but feels the processing required needs some more work on reliability and consistency – but that’s coming.

The power amplifiers in the new Sigma series – the £2950 two-channel AMP2 (above) and £4250 five-channel AMP5 – both use Class D amplification, delivering 200W per channel into 8ohms, with new switching technology developed for the company’s CA-D200 amplifier used in both the power supply and amplifier stages.

This uses controller circuitry to analyse and adjust the dead-band time – the minute fraction of a second during which the amplifier is off in the middle of its switching cycle –, thus reducing the need for negative feedback and requiring only filtering at the switching frequency, way beyond the audible band, rather than the high-frequency roll-off Nauber says is used in most other Class D designs.

As he puts it, ‘some dead-band time is needed, otherwise the amp will go into short-circuit and explode’, so what the start-up analysis does is detect that ‘go bang point’ and then back off just a shade, allowing dead-band time in the single digits of thousandths of a second to be achieved.

The Classé approach, both in the simplification of the processor and the design of the amplifiers, which are slim and cool-running, seems to make a lot of sense to me, and it was interesting that, in the listening room at B&W, we were treated to a program of music in stereo, played through a pair of 802D speakers, with not a sniff of anything surround or movie-related.

That made a welcome change from the usual ‘Here’s our amp and here’s how loud it’ll go’ home cinema demonstration, complete with liberal use of Pixar animation or scenes from Pacific Rim.

Built like other Classé products at B&W’s own factory in Zuhai, China, the Sigma models are designed at engineered at the company’s HQ in Canada, where the team combines what Nauber calls ‘youthful enthusiasm and curmudgeonly experience’. He says the secret of this strategy is that all the clever stuff is done at the design stage, meaning the products can be assembled consistently without the kind of fettling that used to be part of high-end manufacturing.

I can’t help feeling Classé might be on to something with this more minimalist but totally sound-related approach, and initial impressions (albeit with all the usual unfamiliar room/music caveats) were impressive – although I’ll be interested to see how the new products will play with the logo-obsessed AV crowd and those who drool over pictures of the rear panels of behemoth receivers.

I’ve requested review samples of the processor and the two-channel power amp, and I’ll report back when I’ve had time to have a play.

Written by Andrew Everard