Wedded to the bottle.

Unison Research and Croft allow us the opportunity to sample low-powered all-valve amplification. Richard White eschews the Leaks and gives his Klipsches something different to chew on.

Unison Research and Croft are both respected names in thermionic amplification, so the chance of comparing an amplifier from each of them was not to be missed, although a direct comparison is not as easy as it might seem. True both these amplifier packages are comparable in price and both use valves. Fromthere on, the differences start to outweigh the similarities.

Unison Research's S2 is a class A ultra-linear design, driving two EL34s in single-ended configuration. Low level amplification is in the safe hands of a pair of ECC82 double triodes. Four line inputs are provided - no phono stage - and a choice of 8 Ohm or 4 Ohm loudspeakers. The S2 is long on style; its transformers are neatly covered by a ventilated box; the valves sit in ceramic bases in the open for all to see; nicely finished wooden fillets add a hand-crafted air. Controls are simple: ON/OFF at the back next to the kettle lead input; volume, channel and tape monitoring by heavy 'feel good' controls on the front.

BOTTLED UP

If Unison Research have chosen a quietly conservative route, Croft is tracking cross country. The preamplifier, the Vitale, walked off with a deserved four globes in our recent review, and features four channels including MM phono, separate volume controls for L and R and three valves concealed within the sheet metal case. The Troubadour power amp is output transformer-less (OTL) which remains a 'good trick if you can do it'. In place of the usual transformers for matching loudspeaker load, four large double triodes output direct, with decoupling via good quality foil capacitors. Miniature double triodes drive these monsters. A slight word of warning is needed here. Valve amplification is a warm business; the Troubadour would do very nicely as a coffee-pot warmer if one were foolish enough to try such a thing, so a well-ventilated shelf place is essential.

Neither of these packages will blow your head off with inefficient loudspeakers: the Croft manages about I 1OW into 8 ohms and the S2 about the same, depending on the reactive vagaries of the loudspeakers used. In order to hear anything worth hearing, it's necessary to employ sufficiently 'sensitive' speakers; there are plenty out there at most budgets if you search well. Using a low-power amp to feed efficient speakers is an approach somewhat at variance with that most favoured today, but it can and does produce beguiling results, all things being equal. It is a technique which I favour personally, so I was not entirely surprised when these amps came to show off their paces driving my resident Klipsch Heresy Its (93dB/W/m).

Unison Research have certainly not stinted on their transformers if weight is anything to go by; the complete S2 weighs about 301b. Unison claim 'painstaking' (sic) research into the output transformers, which is a good thing for a single-ended design which does not benefit from the 'self-correcting' characteristics of push-pull. Integrated amps are naturally self-contained and as such are less trouble to set up than pre-power sets. Matched pairs of valves are specified for the S2's input/driver stage, although this should not be super-critical with automatic bias; those supplied are indelibly marked L or R on their undersides.

Croft's Troubadour is supplied without its valves fitted too. All are oriented horizontally on the chassis; with horizontal valves, especially those without retaining clips, it makes sense to use a little spot of contact oil.

A Hi-Fi World stalwart, the Minnesota Orchestra's vibrant recording of Stravinky's Firebird on Reference Recordings opened the bowling. Once Unison's S2 had settled into its stride, l was struck by its very lush way with the orchestra. Whereas some of the more zippy solid-state amps can make for an uncomfortable earful, the S2 adopted a very silken approach. In short, the sound was very much what people seem to expect from a valve amplifier; a smooth, mellow sound; detailed enough but without any distressing sharp corners.

SOUND STAKES

The Troubadour certainly didn't spit in my eye either, but it manifestly had not been engineered with warmth as the prime consideration. Perceived dynamic range was if anything a little wider than the S2, with more than a hint of jaggedness on the brass and percussion ?the Croft sounds fast whereas the S2 sounds more relaxed. In particular the amazing efforts of the woodwind section, which has many cameo appearances in this work, seemed happy with either the S2's warmth or the Troubadour's saltier approach.

I remarked on the Vitale/Troubadour apparent dynamic range; given a suitable thickness of texture, the Unison swiftly caught up, driving real power to the (admittedly very fast) Klipsch speakers. One game played and into tie-breaks already!

Interestingly, it was with more relaxed material that the Croft drew distinctly ahead: Diana Krall's 'come and get me' vocals are closer to easy listening than to true jazz, so I fully expected the Unison amplifier to contribute the appropriate cock-tail warmth and glamour. Instead, the amplifier's comfortable sound put Miss Krall a shade off the boil; it was the Croft combination which restoured the edge necessary to keep things smouldering. Neither amp showed any difficulty over usual benchmarks like stereo imaging and both gave exceptional sound stage breadth.

It appears that Radio 3 is positively gorging itself on chamber music at the moment and tuning in, I found the Wallace Collection wrestling with some Bach.The S2 made a very neat job of this intimate occasion and perhaps was unduly forgiving of other presumably assiduously researched details.This is a most comfortable amplifier and I guess is what many transistorised people expect of valves. The Vitale/Troubadour's more sparkly touch was less forgiving of poor balance, sore throats, singing off key and sloppy entries - the all too common paraphernalia of the small-scale music movement.

FINAL THOUGHT

You pays your money, you takes your choice. Unison Research have crafted a fine, well-behaved low power amplifier here. If it's a little smooth for my taste, very many people will welcome it with open ears. Croft's unusual OTL Troubadour with its companion Vitale is altogether more exciting. The Croft package is dearer too, although you do get an excellent MM phono stage thrown in.

Much must depend on the loudspeakers: weighing up what I've written, the first step with either of these fine amps is to buy the 'speakers which will let them shine - don't hook up your 83dB bookshelf models and hope for the best: it's not to be had this way.

 


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