The KT150s do need to be biased to ensure they run better for longer. Bias is adjusted using the supplied long red flat-head device (a bit like a thin drinking straw mixed with a screwdriver... the tool, not the drink). This turns the groove cut into the top of four small potentiometers visible from the top plate, until each of the four little red LED bias indicators go out. Notionally at least, you need to bias the valves just once at the start of their working life, but I’d recommend checking them every six months of so for drift. That being said, both KT150s and modern circuitry are extremely stable, and maybe that one-time bias is all you need.
The ART300 is the natural partner to the GAT preamplifier from the brand, and not just in a visual styling sense. The output impedance, gain structure, and even the circuit design are all designed to be a perfect match for the ART300 (more accurately given the time-line, the ART300 was designed to be a perfect match for the GAT). If you do use it with the c-j flagship preamplifier – and I imagine most will be sold in this exact configuration –remember to invert phase at the speaker terminal end because the GAT’s output inverts absolute phase. Speaking of inputs and outputs, the ART300’s lone RCA input and pair of speaker terminals are relatively minimal.
The valve complement is fairly minimal, too, with just two 6922 tubes in the input and phase inversion stage, and two pairs of KT160s in each chassis. The company doesn’t exactly discourage tube rolling, but it strongly recommends using the supplied valves and buying replacement valves from the manufacturer or agent. This is because it claims the selected tubes are chosen specifically for their sonic abilities. The ART300 retains the classic and distinctive gold livery and font set of c-j devices old and new. There is a single large slow-start button on each amp and there is a valve cage if you are worried about Swedish polar bears getting heat rash, or something.
The slightly dated-looking but functional manual is free from illustrations, but the amplifier is reasonably self-explanatory in set-up and use. OK, if you’ve never pushed a valve into its own seat, you might want some steering, but I seriously doubt this applies to any ART300 owners.
There is no discussion of running in the ART300 in the manual, but from experience, any amplifier sporting a lot of Telfon capacitors is going to take a long, long time to come on song. Fortunately, the conditioning period is usually an unpunctuated continuum from sounding pretty good out of the box to sounding remarkable a few weeks later. But there is no period of amplifier personality disorder, where some days it powers up with the voice of an angel and other times like it had spent the night shouting Tom Waits impressions while on a cheap whiskey and cigar-smoking session. Instead, you are on a slow but gentle boat to wowsville.
In terms of sound, I’m pretty sure the term comes from tennis (although cricket, childbirth, and haemorrhoid treatment have been mentioned in dispatches), but what the ACT300 excels at is the ‘unforced delivery’. Music is neither strained nor constrained in passing through the ACT300 amps, and in listening to this wonderful amplifier group, you quickly realise just how rare that quality is in audio. While I am loathed to use audiophile recordings to highlight such things, ‘Yearnin’’ by The Three [Inner City/East Wind] is a perfect arbiter of why this is important. This slick piece of mid-1970s Tokyo-recorded dinner jazz by a piano trio can sound like it’s either trying too hard or is so laid-back it could have been drugged with antipsychotics. Here, on the other hand, it’s just effortless... the unforced delivery.
This can give the wrong impression; ‘unforced’ can be mis-read as ‘relaxed’, but that impression goes away when you play something like ‘Georgio by Moroder’ from Daft Punk’s Random Access Memories album [Columbia]. Instead, that unforced delivery makes the amplifier let the music take control, from the click-track to the crescendo ending (falling back to the click track once more), it gets wild and raucous, as it is supposed to. It’s not that there is an absence of character here; in fact the c-j sound is ever present, but it is also alluring and draws you deeper into the music so you can’t help but feel that slight richness is actually accurate and most other devices sound a bit too thin in comparison.
Track after track in genre after genre was played and, in each case, the ART300 teased out the best in the music. Even something that has no nice side – the harsh, shouty ‘Boss’ by Little Simz [Grey Area, Age 101] – benefitted from the ART300 effect, as it drew you in deeper to the recording. I’m not sure that’s a good idea – this is a very raw break-up album that screams at you – but it puts you right in the heart of the music.
Those who are obsessed by the beat, to the exclusion of equipment that doesn’t emphasise the rhythmic aspects of a performance might find the ART300’s sound beguiling, but possibly too cerebral. The rhythm of a piece of music is well played on the ART300, but it isn’t front and centre of the music unless rhythm is front and centre of the recording. In other words, if you want a system that accents the rhythm, the conrad-johnson plays a more even hand. Personally, I don’t see that as a criticism; the reverse in fact. But there are those who effectively define their music by its beat and will pass on the c-j for being too accurate. More fool them.
On the other hand, if you are a bit of a soundstage buff, the ART300 will be almost perfect for you. If there is an emphasis on particular performance aspects of the sound in the ART300, it’s in the soundstaging. Partner it with loudspeakers with equally good imaging properties and give it some recordings with outstanding spatial qualities (for example, Rachmaninov’s Symphonic Dances, recorded by Zinman and the Baltimore Symphony Orchestra on Telarc), and the sense of layering of instruments, of individual instrument voices within the stage, and how those voices blend together, are all state-of-the-art in ultimate terms. The soundstge has perhaps greater depth than width, but this is perhaps more that for once soundstage depth is properly presented.
These flagship amplifiers are wonderful, in that they convey the music with such sublime grace and charm, you cannot help but be drawn deeper into whatever music you are playing through the conrad-johnson ART300. It says, ‘music need not be a roller-coaster, unless you want it to be.’
In sum: Cor!
Type: single-ended valve mono power amplifier
Inputs: 1× pair single-ended RCA stereo line-level inputs
Outputs: 1x pair multi-way loudspeaker terminals (4Ω output)
Tube complement: 2 × 6922, 4× KT150 per channel
Frequency response: 20Hz–20kHz ± 0.25dB
Power output: 300W (from 30Hz-15kHz, at no more than 1.5% THD into 4Ω)
Sensitivity: 1V rms to rated power
Hum and noise: 108db below rated power
Input impedance: 100kΩ
Dimensions (W×D×H): 48.3 × 41.4 × 22.2cm
Weight: 33.11kg per channel
Price: £41,995 per pair
Manufactured by: conrad-johnson design, inc.
Distributed in the UK by: Audiofreaks
Tel: +44(0)208 948 4153