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Harrison X150 amp

When IT man Nick Graham undertook his recent tour with the Explorers, we asked him to try one of the new Harrison Information Technology - H.I.T. - power amps for his keyboards backline. He borrowed the H.I.T. X150, and here's his report.

When it comes to power amplifiers, the requirements of today's keyboard player are much the same as any user of high-quality amplification, be they studio engineer, P.A. company or hi-fi addict. Purity and transparency of sound are essential for accurate reproduction of the incredible range of sounds possible on modern electronic keyboards - any colouration of sound by the amplifier is strictly not required.

Coupled with this (and equally important) is ruggedness and reliability - what good is the cleanest-sounding power amp in the world if it doesn't work perfectly every time you switch it on? Happily, I can say with confidence that the H.I.T. X150 sets extremely high standards of sound quality and reliability. Rack mounted along with a mixer and other effects/interfaces, it was humped round 26 dates in Britain, and airfreighted to Holland and Italy, without so much as a hiccup (I know how to spell hiccough, but it looks wrong!).

The X150 is the smallest in a range of five H.I.T. (Harrison Information Technology) MOS-FET stereo power amplifiers, the largest of which (the X1200) develops 600 watts per channel into a 4 Ohm load. In the handbook they're described as '2nd Generation MOS-FET' amplifiers, and although I can't pretend to understand the technology, Mike Harrison, their designer, claims that they are a significant improvement on earlier MOS-FET designs. Certainly the specifications for the X-Series are impressive; to quote the handbook again, 'transient intermodulation distortion (TIM), difference frequency distortion (DFD) and total harmonic distortion (THD) are all so low as to be close to the limit of test equipment capability.'

Since the X150 was the one I checked out. I'll now try to concentrate on reviewing that model. It has, in fact, quite a modest output of 54 watts per channel into 8 Ohms, or 80 watts per channel into 4 Ohms before clipping (In bridged mono mode it will produce 150 watts into 8 Ohms). This, you may think, is not an awful lot of power, but remember that this amplifier can be driven to full output without any appreciable distortion. However, even though I like to monitor at fairly low levels on stage (being a keyboard player, not a guitarist), I found on occasion that I was driving the amp to the point where the output peak level indicators were flashing on. No problem; these indicators are designed to light at 1dB below clipping, thus avoiding nasty distortion! The thought did occur to me, though, that perhaps I could have done with the extra headroom which would have been provided by the larger X300 version, giving approximately double the output of its smaller brother.

Both the X150 and the X300 are cooled by convection and radiation of heat from the chassis. Thus no special precautions regarding cooling need to be taken - my X150 was racked tightly with a number of other units. As far as external connections are concerned, the X150 had binding posts for speaker outputs, and XLR inputs (balanced or unbalanced, depending on how you wire up the plug). Since the unit is only 1 3/4" high (1 Rack Unit), it would be physically impossible to incorporate any other connectors in the rear panel, but it does mean that the X150 has to be permanently racked with the speaker output binding posts connected to suitable output connectors mounted on a separate plate. Of course, all the other models in the range are bigger and therefore have a much more comprehensive selection of connectors on the back panel.

Finally, I must mention two other features incorporated in the X150. Firstly, the headphone output was very useful and would have been even more useful if it had cut off the speaker outputs when the plug was inserted (purely a personal preference). Secondly, the little switch on the back which disconnects the amplifier earth from the mains earth instantly eliminated a hum loop on several occasions. This kind of attention to detail coupled with exceptional sound quality, add up to an excellent amplifier suited to any application where high-class reproduction is required. A word of warning, though, to any prospective users: an amplifier of this calibre needs a pre-amp and speakers of equal quality. Don't expect to get the clarity of sound I've been describing from your battered old 4x12. All the links in the audio chain must be strong - one weak one, and all the efforts of Information Technology will be for nothing!

RRP £354.72 Inc. VAT

More details on H.I.T. products from Harrison Information Technology Ltd., (Contact Details).

Previous Article in this issue

Yamaha's DX21 FM Digital Synth

In Tune - Copyright: Moving Music Ltd.


In Tune - Jul/Aug 1985

Donated by: Gordon Reid

Gear in this article:

Amplifier > Harrison > X150

Review by Nick Graham

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