Having scored so highly the Graham Slee Proprius Mono Power Amps are currently with second reviewer Ian Ringstead to ascertain whether they will receive the coveted Hifi Pig Outstanding Product Award. This review will be published shortly. Read Janine Elliot’s first part now!!
Over the last half year I have done a few reviews on products by Graham Slee, a highly religious and uniquely kind personality, whose ideas are well known but not as often reviewed as I feel they should be. Best known for the small phono and headphone amplifiers, his background was making mixing desks and amplifiers for the BBC in the days when even the girls wore suits. The days where you not only took pride in the work you did but also what you wore. I loved those days. So, sit me down (not in a suit) listening to his 25W Proprius monoblock Class Ab power amps, connected with Ecosse MS2.3 cabling to Graham LS5/9 speakers and I am reliving my 25 years at the corporation. The Graham S and Graham A combination are just meant for each other. 
The Proprius, like most of the Slee product base is simplicity in looks, but this hides some really good engineering design inside. No mass produced tech which is designed to woo in the listener with either over-accentuated bass or zillion Hz topz. This is about music; this is real class Ab – not D or T; this is about ease of listening, and an amazingly good amount of audio level despite the low power numbers; all those sudden bursts that many an amp needs hundreds of Watts in reserve to deliver with any meaning, are catered for with comfort here, even when I connected them to my 83dB sensitivity 15ohm LS3/5a speakers. Rated at 25watts into 8 ohm or 45watts if into 4ohm, each unit costs £645.90 and with XLR balanced in and conventional loudspeaker terminals is no mean product. The Proprii playing Sibelius 2 (Thomas Søndergård, BBC National Orchestra of Wales, Linn Records) via Fiio X5 into Slee Majestic DAC with its balanced output is masterfully performed, just as the sound engineer would have heard it. I could have been sitting behind the mixing desk. Memories from my past aside, this was a very musical and detailed performance easily justifying its price point. This is a truly dual-mono amplification system, allowing improved stereo separation. The small unit size is helped by having the 120 Watt switch-mode power supply in an external unit, and comes complete with a mounting kit so that it can be piggy-backed to your loudspeakers. That is where the balanced input really comes in, though it worked just as well unbalanced mode in the hi-fi rack. All that is missing is a power switch. I miss that as it means every time I turn the unit off or on I get a burst of current through the speakers. Whilst this is minuscule into the Graham Audio, through my aged Chartwell LS3/5a I needed to turn down the volume controls on the Proprii to protect the Kef B110 bass/mid driver. These amps are really designed to be kept on continually. Whilst the Proprius is designed to run on full power, having a volume control on each channel means it could be used as a single-input integrated. Despite its diminutive appearance this exudes quality, including rugged 15 Amp 30 MHz output transistors, high-end professional gold plated XLRs on input and power sockets, and an effective head radiator case for cool class Ab running. Frequency response into 8 ohm went up to 47kHz with no more than 0.1% distortion and S/N A-weighted at 87dB. OK, nothing mind boggling, but bearing in mind this is a discrete component design in a 105 x 55 x 205 mm box, there is nothing diminutive about its performance. There was nothing wanting from the sound I heard, and no confusion in the sound, whatever music I threw at it. This is professional audio amplification, often reminding me of my modified Quad 405’s from years’ back. Each mono-block comes complete with its own frequency chart showing that, as is very important, specification between units are as closely matched, much as was the tight consistency of quality control between every single manufactured LS3/5a, that I also paired for this review.
Playing Nielsen Symphony No 3 (New York Philharmonic Orchestra, Alan Gilbert) first movement DSD recording via coaxial output from my aged Kenwood DVD-A player into the new NuForce DAC-80 gave a compellingly purposeful performance. At 09’30” even I jumped out of my seat as the music took to a new level. The instrumentalists of course remained in theirs. 
These amplifiers are not just for classicophiles, as Graham says;
“With an ever increasing audience of rock lovers, I set out to design products to not only sound fantastic with symphonies, choral music, quartets and audiophile jazz, but also to reproduce rock music in such a way as to provide fun listening – to provide those air-guitar inspiring moments!”
He decided this after listening to Led Zeppelin ‘Kashmir’ in a hi-fi shop and wondering why it sounded flat and compressed. Indeed, in the 1970’s Graham was himself a DJ, and also building on-the-road equipment. It was at this time he began developing phono preamps and headphone amps The Proprius certainly has enough welly to make even the most ardent Progressive Rock fan happy. And whilst this baby couldn’t compare anywhere near my Krell KAV250a in terms of power output, size or cost, this was no mere sibling. This had grunt, with an exceptionally dynamic and energetic soundstage from the deepest lows to the tizzling tops. I have sat on this power amp for a considerable time now, and every time I switch it on I get surprised just how good it goes. Whilst China-built packages can sound really good nowadays, I’m not interested in cheap prices or spec or buttons or lights. I just wanted to listen to musicians, and through this kit I most certainly could.
Suzanne Vega Tom’s Diner gave a sweet but solid rendition of her solo voice in all its glory. All frequencies were clear and musical, from the lowest to the highest. Through the LS5/9s this was one of the best performances I had ever heard at any price.
Patricia Barber ‘Live, A Fortnight in France’ had excellent depth of field, with each and every instrument played just as the musicians intended, with me there in Metz, La Rochelle and Paris. Thoughts of my 10W Valve Leak Stereo 20 came to mind; whilst the 50s design is low in output and has a technical specification today’s designers would be embarrassed to quote, it still sounds remarkably musical. That this 21st Century £1299 all-in package can sound as good as it does is indicative of Slee’s compulsion with creating the very best. Today’s “new” is being small, as shown in minuscule products such as Project’s MaiA, or the simplistic yet beautiful Roksan Oxygene series or the respected Devialet creations, so there is definitely a place for the Slee. As a woman, as well as liking to have less to dust, I would ask whether there could be versions in different colours; perhaps Pink (appropriately for HiFi Pig). Having different finishes not only fits into everyone’s living room and taste but also makes it more of a designer product, and therefore more expensive looking. Yes, I know it would add a few pounds to the cost, but for an amplifier as good as this would add to interest from those who might otherwise not choose a Slee.
CONCLUSION
For a complete Class AB dual mono-block power amplifier at under £1,300 is a feat in itself, but this system is more than that. It harnesses many years of experience of breathing in solder fumes and scratching of the head to create something that Graham himself is happy to put his GPSAudio dove on the front. The dove is portrayed as white and gentle, sweet and loving. This amplifier is certainly something I love, but the sound is not a white wash, nor is it only gentle. This is real Class A in a pint pot, and well worth the price.
Sound Quality – 8.8/10
Value for Money – 8.8/10
Build Quality – 8.2/10
Overall – 8.6/10
Janine Elliot
Having scored so highly the Graham Slee Proprius Mono Power Amps are currently with second reviewer Ian Ringstead to ascertain whether they will receive the coveted Hifi Pig Outstanding Product Award. This review will be published shortly. To find out how Hifi Pig scores products please read our frequently asked questions section.
