First, a quick reminder: the Home THX standard was originally conceived by Lucasfilm to ensure a quality benchmark for AV components.

The front-end processing adds a gamut of tweaks to the audio signal. When it comes to power amps the basic Lucasfilm ethos states:

'The power amplifiers should be unconditionally stable, have a power output in excess of 100W per channel into 8 ohms, have low distortion and wide dynamic range'. The quote is from Lucasfilm's Home THX Design And Licensing Manual.

You might think that such criteria is so laudable that most credible manufacturers would build to these standards anyway - who needs a THX badge to prove it?

Think again. In our experience at HCC, if a maker can cut corners it will. That's commercial competition. Hence we see amplifiers where the rear channels are driven by just one set of output devices, and others that have puny power supplies totally incapable of producing true home theatre 'slam'.

Because power amps are hidden from sight, some makers give little mind to their performance, both on external and integrated amps.

Against this background comes the £725 Rotel RB 985 - a 5 x 100W power amplifier that delivers a mighty 40 Amps peak current and is THX-approved.

Rotel's philosophy appears to be that amplification is everything - yet it need not cost a fortune. The company is into making black boxes where the outside is plain yet the inside reflects quality sonic design.

Boring Black Box

In terms of buttons there's not much to see. A mains switch - that's all. You also have five protection LEDs (one per channel) that light briefly at power-up and illuminate should the amplifier overheat.

Around the back are phonos for five channels plus a female DB25 input that groups them all together. Used alongside a THX preceiver (or processor) with a DB25 output, it makes interconnection very neat and tidy.

One niggle is the binding posts. These accept 4mm banana plugs (you'll have to remove the blanking pips but this is no problem) or bare wire. Trouble is, there are no 'teeth' to grip the wire. It's all too easy for a strand of copper to whisker across and produce a dead-short. Our advice is to take great care when using bare wires - better still, use plugs or spade terminations.

Twinned with technics

The arrival of the RB 985 happily coincided with the delivery of the Technics SA-TX50 THX receiver. As it sports preamp outputs, I partnered the pair together, using my reference Jamo THX loudspeaker outfit.

By re-plugging the preamp outputs I used the Technics internal power amps to drive the Jamo subwoofers (2 x 100W) and the Rotel RB 985 to drive the more critical left, centre, right and surround speakers.

Wow! What slam. My old favourite Terminator 2: Judgement Day was revisited in all its robot-rumbling, missile-firing glory.

Although the Technics receiver is good value, it's not a muscle box. But teaming it with this Rotel dragged some thrilling THX from the Technics front end. Cutting out the harder, gritty emulation of the Technics power stages did the audio a power of good. All the way through the movie it was the same - the RB 985 was richer and warmer. On the 'I need your motorbike and clothes' sequence, Arnie's Harley had a deep throaty roar. Wonderful.

And it's not only bass extension that's satisfying. On Jurassic Park the 'Welcome to JP scene' reveals a wonderful stereo score as the camera gazes upon the dinosaurs.

The soundstage had an almost primeval depth.

Needless to say, the TV-shaking footfalls of the T-rex truly sounded frightening when set to the recommended 75dB level (using a meter and careful calibration). The Technics presentation, in comparison, was loud, but hard.

Serious slammer

Top marks to Rotel for making a multi-channel amplifier that sounds great as well as suiting the pocket. Given that you get five channels of lush attack - an instant upgrade from the compromises found in integrated amps - the £725 asking price is very fair.

And brickbats? None, other than the fussy output terminals. I'd like to see a seven- (or six-?) channel version to accommodate THX systems that lack powered subs - but as more speaker makers are turning towards active THX subwoofers, it's unlikely that Rotel will take the bait.

If you are in the market for a punchy upgrade to your Pro-Logic outfit or are seeking THX slam without spending silly money, lend your ears to this brilliant black box.

We used it to provide an instant panacea to Technics' underpowered THX receiver, and it might well work the same wonders on your system.

Highly recommended.