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conrad-johnson ART300 mono power amplifiers

conrad-johnson ART300 mono power amplifiers

Back in the late 1970s, when US high-end began to grow out of a burning desire to not put up with mediocrity, there were two main brands pushing valve amplification where all else was solid-state; Audio Research, and conrad-johnson. Others came and went, yet more joined the fray and continue to make outstanding audio devices that use ‘hollow-state’ technology, but it ultimately comes down to these two brands who put their respective flags in the ground. They are in part the reason we have a high-end industry, and in great part why that industry still uses valves as amplifier devices.

When conrad-johnson launches a new flagship valve-based mono power amplifier, the audio world should take note. This isn’t an everyday occurrence, and perhaps more than any other brand, c-j has stayed true to its original direction. Yes, there was a change a few years ago because that original direction sounded a little too laid-back for modern ears, but the performance of the ART300 monos define a new generation of c-j designs, as did the ACT and the Premier line of power amps before it, harking right back to the Premier One from 1981. What these flagship designs offered was valve performance mixed with the kind of power output normally associated with solid-state designs. So it is with the ART300; as the name suggests, these power amps deliver 300W per channel and do so thanks to two pairs of KT150 output tubes in each chassis.

The KT150 is very much the ‘now’ valve, and since its launch and wider availability, it has become almost standard issue throughout the high-end audio world. For good reason, too; it has that great combination of linearity and power that every valve amp maker craves. Yes, there are curmudgeonly types who are convinced that any tube designed after the War is somehow compromised by the trappings of modernity. Some of the really out-there types are keen not to be drawn when asked, “Which war?” But three-watt power amplifiers capable of just about driving a 1920s cinema speaker are not really practical in the real world. Although the days of super-difficult loudspeaker loads are largely behind us, there is nevertheless a need to make a valve amplifier that behaves sonically like its hollow-state predecessors, but with modern power delivery and damping factor needed to drive more modern speaker designs. That’s something c-j has been doing right since before Thatcher got elected.

Paradoxically, alongside the launch of the ART300, conrad-johnson has also launched another limited-edition power amplifier called the ART27A, and where the ART300 is a 300W powerhouse, the other range-topper puts out just 36W per channel in Class A from its quartet of KT88s operating in triode mode. I’m sure some might think this sends mixed messages, but I think it’s c-j addressing two sides of the 2019 tube amp market; the demands for more power and more grace, That being said, the ART300 is no slouch in the grace department in its own right, as we shall see later on.

The conrad-johnson ethos is a smart one. The ART300 mono amplifier is essentially two ART150 amps, permanently switched to monophonic operation. Or put another way, an ART150 is one channel of the ART300, with two sets of input boards and stereo output. It’s an economy of motion thing. Once again the numbers are limited; 250 stereo amps and just 125 pairs of the monos. in essence all three power amps (the ART27A, ART150, and the ART300 tested here) are part of c-j’s 40th anniversary.

The audio circuit of these amplifiers has just three elements, each as simple as possible, and each essential to the operation of the amplifier. A voltage gain amplifier (a single triode) is direct-coupled to a cathode coupled phase inverter (each phase handled by a single triode), which in turn drives the output stage. This drives two pairs of the aforementioned KT150s to deliver 300 Watts into eight ohms. A small amount (about 12 dB) of loop negative feedback is used to reduce distortion and to produce a sufficiently high damping factor to control reactive modern loudspeaker systems. Separate, low impedance, discrete DC power supply regulators are used with the input and phase-inverter stages, isolating both stages from the power demands of the output stage.

The company has long been a proponent of high-performance parts even in its more affordable amplifiers. So, the ART300 is going to bristle with top-notch components as a matter of course. So, the ART300’s resistors are precision laser-trimmed metal foil types, and CJD Teflon dielectric capacitors are used for coupling the inverter stage to the output stage, and to bypass the large value polypropylene capacitors in the regulated power supplies. Proprietary wide-bandwidth output transformers are also used and are claimed to “contribute to excellent high frequency performance.” Even the machined gold plated OFC connectors and the internal wiring were chosen for their sonic benefits, and the brand’s long-standing relationship with Cardas pays dividends here.


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.

URL: conradjohnson.com

Distributed in the UK by: Audiofreaks

URL: audiofreaks.co.uk

Tel: +44(0)208 948 4153



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