The aforementioned valve complement consists of matched pairs for the output valves, identified for installation as the valves are packed separately for shipping. The 6DJ8s are employed in a differential cascode circuit for the input/driver stage, with a regulated B+ supply. And despite the sensible price, all of the components are designer brand luxuries, the labels including Cardas, Holco, Vishay, Wonder Cap, Rel-Cap, Wima and Solen. The wild mix of components from so many brands implies that much close listening was undertaken to choose the best make for each task.

Although an assembled unit was supplied, the company also sent along a construction manual, one which is reminiscent of the lucid guides which accompanied Dynaco amps. According to the sales blurb, a DIY-er should be able to assemble a Sonic Frontiers amp in around 10-15 hours -- not bad for a $700 savings. Assembling the amplifier also allows you to select a couple of options which, in built-up form, are restricted to dealer or distributor resetting. The review sample was configured to run in regulated screen pentode operation, with full triode operation as an option.

Pentode vs triode is one of the hot debates at the moment, but Sonic Frontiers chose to offer the choice of either, feeling that the ancillaries will determine which setting is best. Rather than tamper about inside, I merely swapped speakers until I hit on combinations which 'sang'.

The other choice to be made is for speaker impedance, which requires only minor rewiring. The review sample was set for 3.5 ohm, ideal as most of the speakers I intended to use for the review had impedances of between 3 and 6 ohms. The other settings are 8 ohms and 14.5 ohms, the latter perfect for LS3/5As and certain electrostatics.

Surprise, surprise: this 50-watter drove the Sonus Faber Extremas to more than adequate levels and worked miracles with the Apogee Stages. True, the former would sound better with a brace of SFS-50s in bi-amplified mode, but they proved an ideal test to find out about the bass capabilities of the amplifier, especially as the speaker's adjustable damping could be called on if needed. But more revealing was the way the SFS-50 worked with the Stages, convincing me even further that ribbons+tubes=nirvana...when possible.

Having lived with a Dynaco Stereo 70, in standard form and with (partial) Curcio modifications, I was expecting 'cleaned-up vintage sound'. This usually means loads of warmth but with the transparency often lacking in older designs. It's a half-way house between the rosy lushness (and flabby bass) of yore and the finely etched precision (and listener fatigue) of solid-state designs, with modern valve amplifiers somehow mixing the bext of both worlds in varying degrees. And this is what the Sonic Frontiers amp does, banishing any notion of vintage origins with a top end which exploits even the Sonus Faber tweeter.

This baby is detailed and clean, but completely devoid of 'hi-fi' edginess or spit. At first, it could be mistaken for the rolled-off filtering effect of aged glass, but it's just not the case. Transients have bite, fine details are as vivid as with the Classé DR-10 and high notes soar rather than taper. Most impressive are the dynamic contrasts in the upper frequencies, which retained their relationships even when the amp was obviously working harder than it should (through the Sonus Fabers).

I was worried that the SFS-50 wouldn't be up to the task of controlling the Stages' bass ribbons, but couldn't make them misbehave unless I turned the wick wa-a-ay up while using material with daft bottom octaves. 2 Live Crew's latest, the Professor Griff's spewings -- rap recorded by a knob-cranker proved to be too much. Back in the real world, though, and the SFS-50 sounded almost as well-controlled as the Classé. All it lacked was the final touch of extension which makes some big tranny amps sound as if they were designed to drill for oil.

Still, the SFS-50 sounded 'bigger' than it had any right to, partly because of the confident bass but primarily because of a wide and tall soundstage. Depth was only so-so, better with the Stages than any of the box speakers I tried, but that's an Apogee trait. But the up-down/left-right capabilities were consistent from speaker to speaker, so the Sonic Frontiers is a room filler in more ways than one.

Having used the amplifier for almost a month, working it hard, I'm pleased to say that it hasn't misbehaved once. Paranoids may wish to run it with the bias reduced by 10% to extend valve life, but I can only think of one area which requires special attention. This amplifier is so cable-fussy that I was going crazy trying to sort out some weird mid-band glare. Two cables stood out from the dozen or so to hand, the latest wire from Symo and Be Yamamura's A.R.T. cable, but I'm certain that others may proved usable. Just keep this amp away from single-strand solid-core, okay?

I'm tempted to call this a Stereo 70 with grunt, but it's much more than that. A hot-rodded Dynaco will match it for mid-band clarity and 'presence', and maybe at the top, but not in terms of dynamic capabilities or bottom octave resolution. I can't wait to hear how it sounds compared to the Dynaco Revived, which -- while looking like a black-clad Stereo 70 -- has benefitted from modern practices.

Can I recommend the SFS-50 to a mail-order purchaser? Am I prepared to spend your money for you, knowing that you can't hear it first unless you fly across the pond? Yes. Which is why I'm ending this review with: