Sugden Masterclass Preamp and Mono Amps Reviewed

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Sugden Masterclass Preamp and Mono Amps Reviewed

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How droll: here we are at a transitional period in audio history, when all of the hooded, scythe-bearing doomsayers are bellowing about the death of stereo, high end and/or hi-fi full-stop, and up pops one of the most impressive efforts yet from a UK manufacturer. Then again, we are talking about whippet-owning, cloth-cap-wearing Yorkshiremen of a known stubborn streak, so we shouldn't be surprised, Sugden being the company which introduced and stuck with Class-A and current feedback in a era when the (small 'c') conservatives of the hi-fi press were championing some of the most unimpressive Class AB transistor travesties ever released. As we are blessed with 20/20 hindsight, it's quite clear now that the Sugden gear of yore was sorely underappreciated.

Read more audiophile stereo and integrated amp reviews from Copland, Krell, Cello, Audio Research, Mark Levinson and others by clicking here.

With Masterclass, Sugden has joined a tiny group of British manufacturers with aspirations beyond Land's End and John O'Groats. But if the nationality of a product affects your decision-making (please, don't buy French), you will probably audition Masterclass against Chord, ATC, Naim's new 'monster', Linn's Klimax and precious few others. Not only are the Sugdens large and powerful, they're costly, if not quite pricey as the Linn and Naim flagships.

Working under the delicious tag line of "Rescuing Music from Technology", Sugden is more than happy to play both the objectivist and subjectivist cards. The company states quite clearly that its criteria include designing for wide-bandwidth with minimum distortion, phase stability, low impedance and power supply stability, all of which are measurable and directly related to matters of dynamic import, including speed, maximum headroom and neutrality. Conversely, (and I don't wish to attribute this entirely to a new staff member with roots in the left-of-centre valve arena) the company also admits that the choice of components, extensive subjective listening tests and other concerns usually associated with audiophilic cultism do influence the final performance.

Could this really be a company born during the era of measurements-only designing? Are they really sweating over immeasurable psycho-acoustic phenomena, gold plated circuit boards, solid silver wires, gold connectors, case materials, semi-conductor structures? So it would seem. What remains unchanged is the handcrafted nature of each unit, built using the Volvo school of manufacture with "individual people being responsible for individual amplifiers." God forbid it should result in cultism in which audiophiles demand that their Sugdens are assembled by specific staff members...

With the Masterclass series, Sugden leaves the cosiness of the uniquely British cottage industry integrated amp, begging direct comparison with the world's finest hardware. We are talking here of a pre-amp selling for �1995 and a brace of monoblocks at �5995 the pair. Serious stuff, indeed.

Addressing every modern requirement this side of home theatre, the Masterclass Pre-Amplifier is a line level stereo unit with one balanced XLR input, four single-ended RCA inputs and two recording inputs, plus one balanced XLR output, two recording outputs and two main pre-amp outputs, with a remote control operating volume and commands for Philips-based CD players, but not source select (at present). It oozes a studio feel, despite the mildly Aztec angularity of the faceplate and the refreshing use of gun-metal grey instead of silver or black. The knobs across the front deal with source selection, standby, source/tape, tape 1 or 2, record out and volume, the record out and standby controls accompanied by red LEDs. The back sports gilded sockets for the above inputs and outputs, plus the primary on/off rocker switch and IEC mains input.

A true dual mono unit, it contains two transformers, a Current Shunt Differential Power Supply, two 'Virtual Transformer Balanced/Input Circuits', two current feedback Class A line amplifiers and two 'Balanced Virtual Transformer Output Circuits'. All circuits occupy a large woven glass fibre, double-sided circuit board and all electronic components consist of the highest quality non-inductive 1% resistors with matching to give 0.1% tolerance, high-grade capacitors and selected and matched semi-conductors. As with the fascia, the casing is aluminium, to prevent induction and magnetic distortion.

Masterclass' pre-amplifier line gain circuit consists of wholly DC-connected, symmetrical cascoded Class A circuitry operating with high-speed current feedback and a high impedance input buffer stage; the latter runs in Class A and is said to be a faster configuration than the normal differential input configuration. The cascoded input buffer is designed for zero offset, while an additional servo system compensates for the smallest offset to allow full DC coupling. Those 'virtual transformer circuits' for the balanced input and output stages employ extremely fast hybrid op-amps with exceptionally low noise characteristics. The whole signal is carried in each half of the circuit which are then added together, due care ensuring that both halves of the circuit are balances so that the load is shared equally; matched resistors guarantee the absolute balance.

Quiet and comprehensive, the pre-amp is a joy to use, with an overall feeling of control and precision, despite an odd feature or two affecting the remote; I suspect that it will be corrected by the time this sees print. Utterly quiet, it acts just as a preamp should: switching sources, feeding power amps with negligible impact on the music. It's so invisible, that you might even convince yourself that it's a passive. And there's no denying its absolute fitness for driving the matching power amps.

Sugden's Masterclass monoblock amplifiers are direct-coupled, Class A, balanced, solid-staters with multi-emitter outputs. The front contains a button plus two LEDS to indicate on/off status, the back an XLR balanced input and gold-plated WBT output connectors. Blessedly, the sides are filled with heat-sinks of the non-harmful variety, the corners rounded and safe as a Fisher-Price toy. The blocky dimensions of 430x320x260 (WDH) make the Sugdens unusual in that they are taller than they are deep.

However un-Sugdenlike the massive 160W-per-unit power rating, the Masterclass is the by-product of three-decades' worth of Class A experience, augmented by awareness of the industry's move toward overkill power supplies. Those within the monoblocks use specially 'cored and wound' high-current transformers, fast-acting bridge rectifiers and very low ESR, computer-grade long-life capacitors chosen for their sonic qualities. Connections are via low impedance silver interconnect wires and a solid-metal star-earthing point, with primary circuitry fitted to gold-plated circuit boards.

A current feedback configuration defines the power gain stages, featuring a high impedance emitter follower input buffer stage with a cascode arrangement, running in true Class A bias. The output stage employs multi-emitter power transistors, chosen for 'ruggedness and musicality', while a servo feedback is used to correct any errors on the input devices and to enable full DC coupling of the amplification stages. All the gain stages in the amplification stages are cascaded for wide bandwidth and minimum phase shift. The bandwidth is also augmented by D.C. coupling which avoids the necessity of signal path capacitors.

Sugden has no intention of reviving the British penchant for unreliability, so the amps have been designed for unbreakability. I'm notoriously easy on equipment, so my usage barely challenged its dependability; suffice to say that leaving it on constantly - warm-up takes - while enjoying four-to-five hour listening sessions elicited not a single peep indicative of problems. For maximum stability of the two parallel gain stages, thermal coupling of the input circuitry is used, augmented by vast areas of heat sinkage; these babies do run to near-scalding levels. A fast acting protection board senses any fault condition at the output and shuts the amplifier down; I never activated it. The aluminium case 'excludes the possibilities of induced magnetic distortion' and 'the problems of capacitive links which can occur in high current high power units has been nullified by the case design which also forms a practical housing for the electronics amplifier circuits'.

With dCS' Purcell upsampler and Delius DAC (the best digital products I've heard) fed by the Marantz CD12 transport, and the SME 10/Series V/Lyra analogue front-end with X-LP phono stage (I didn't have access to the Masterclass stand-alone phono stage at the time of writing), the Sugdens drove Wilson WATT Puppy 6 via Transparent Ultra cables throughout. Balanced operation was so clearly superior to single-ended, including the output from the dCS components, that I didn't bother with it after a brief burst. Due to the mix of the Wilsons' sensitivity and the Sugden's more than ample output, I barely worked these babies, the volume control rarely covering an arc in excess of 90 degrees.

Read much more of the Sugden Masterclass review on Page 2

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