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conrad-johnson ART27A stereo power amplifier

conrad-johnson ART27A stereo power amplifier

The conrad-johnson ART27A stereo power amplifier is a somewhat peculiar and non-standard product within the amplifier portfolio coming from the Virginia, US manufacturer. And it’s peculiar for several reasons. First and foremost, c-j amplifiers were always and are still very much traditional push-pull Class AB affairs which, if and when applied with creative wisdom and knowledge of audio electronics, yield respectable power output and a fundamentally good sound quality. Depending on the chosen output valve type and the number of pairs per channel, c-j designs regularly give from 60 up to 300 Watts per channel into any impedance. In short, they can drive almost anything with cones, domes or panels. Secondly, c-j power amplifiers have been renowned for a very conservative degree of hardship their output valves are ever submitted to; in other words, they run on a moderate bias current per valve thus vastly increasing the longevity and reliability of each one of them. This is more than just cost saving; conrad-johnson and its fan-base strongly hold to this being one of the secrets to excellent sound quality.

Paradoxically, alongside the launch of the ART300 mono and the ART150 stereo, conrad-johnson also launched another limited-edition power amplifier called the ART27A. The trio formed c-j’s 40th Anniversary line-up. Where the ART300 is a 300 Watt powerhouse, the other range-topper puts out just 36 Watts per channel in Class A from its quartet of KT88s operating in triode mode. Read that bit back to yourself if you are a c-j amp owner because it might take some time to settle into the ol’ noggin. 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.

Enter the ART27A. Externally, very similar to one of the ART300 monoblocks but for the missing cosmetics of the acrylic/metal encapsulation of all the valves. And that is where all the similarities end. Each channel delivers 36 Watts of pure Class A power through a carefully selected and matched pair of triode-coupled very special Gold Lion KT88 valves. The driver (input) section of the circuit consists of three Gold Lion ECC82 double triodes. One of them is shared between the channels at the very input, while the other two follow suit with their full individual capacity per one audio channel respectively. It goes without saying that very high quality Lundahl output and mains transformers have been used, as well as the usual plethora of conrad-johnson’s proprietary Teflon (PTFE) capacitors and Vishay resistors all over the power supply and audio circuits. The practical result of this, typical and established approach is a power amplifier of an extremely low level of circuit noise, excellent grounding and, also, a virtually non-existent amount of mechanical noises usually associated with transformers and chassis resonances. Amplifier output is coupled to speakers through those aforementioned premium wide-bandwidth output transformers optimised for Class A operation of triode connected KT88. A c-j tradition, pure copper speaker terminals and rhodium plated input RCA sockets come from Cardas Audio.

 

The downside to the high-grade component roll-out is those PTFE capacitors are notorious for needing an almost eternal run-in. Fortunately, the ART27A circuit doesn’t seem to mean that has good days and bad. Instead it starts out good and matures with age. In pure listening terms, the cynical have argued that those caps only really show what they are made of by the time you wear out the first set of valves! 

Low power, Class A triode-coupled or single-ended power amplifiers are meant to be used in conjunction with high-sensitivity (efficiency) loudspeakers in order to reward the listener with a, somewhat unrealistic, but nevertheless, subjective impression of being able to reproduce even the most complex musical material with no strain and ample (subjective) dynamic and resolution headroom. And, as Jeff Fischel, contemporary top-dog of conrad-johnson likes to add – in small to medium size rooms of up to 25 sq.m. Lo and behold, so it may be, but we decided to put the ART27A to work in considerably more laborious conditions. Why? Because only if you push something close to or beyond the limit, you may be able to realise the actual true potential of the device under test. So, the ART27A had to, for the purpose of this review, deliver in a fairly large room and connected to loudspeakers of no particular high sensitivity (under 90dB) and of very serious demands in every imaginable respect. Demands that even power amplifiers delivering hundreds of watts of undistorted power would not necessarily meet.

The bottom line is that the ART27A admirably sailed through all the pieces of less and more complex musical material it has been exposed to and returned a very confident and stable sound. It did this at unexpectedly high volume levels without running out of steam, compressing the natural dynamics of any of the music it processed, without even softest trace of clipping. Precision, purity, palpability and poignancy would be a quartet of suitable attributes combined with a highest degree of 3D soundstage rendition, superb musical transparency and, above all, musical clarity and transient speed only Class A circuit design approach can possibly give.

Let us, however, travel back to reality for a moment. Two crucial qualifying statements about the ART27A before misconceptions creep in. When combined with the very best high sensitivity loudspeakers of suitable size and used in rooms of appropriate dimensions, ART27A will play any type of music as loud as you wish with total confidence, stability and guts. From a small combo to any of the Mahler or Bruckner symphonies. If used in any other way, it will sound at its best even if the speakers and environment in case may not suit it ideally, for as long as combined with equally capable or superior other members of the audio system in use, its limitations (because of the relatively low power output) will reach up to, let’s say, “early Beethoven symphonies at any level.” Above all else, it retains musical complexity at reasonably high levels with total comfort and ease.

The overall sonic signature of the ART27A can be defined as “realistic musical precision”. That means an even tonal balance with a very broad midrange covering beautifully what is contained within most music. Treble is sweet and extended without being glassy, while anything happening below 50Hz or so maintains control and sufficient amount of body without starting to wobble or lose coherence as power may become in a somewhat shorter supply. Most importantly, the whole spectrum is successfully integrated into a harmonious entity serving well any genre of music. In a way this is approaching the best of both the solidity and presence of traditional push-pull designs, with the lithe, liquid and languid sound of single-ended. 

Depth, width and height of the soundstage are remarkable, most likely owing to the Class A operation and, as some would say, not too many Watts.

I have been deliberately circumspect in the nature of the music played here because the ART27A is uniquely well placed to play everything it receives with equanimity and poise. I’m probably not the biggest proponent of Black Metal or Japanese Death Jazz (although I do have at least one disc of both genres in my collection), I’m confident that the ART27A would make an equally good fist of both of them, then turn its hand to Ukrainian folk, then disco, then throat singing without turning a hair. Best of all, enthusiasts of all these genres and more would look to the ART27A as the amp best suited to play ‘their’ music. And that’s perhaps the great joy of the ART27A; it’s the amplifier for people who want that great audio performance found in products elsewhere in the c-j stable, but who want an immediacy to their music too. 

An amplifier that is insensitive to types of music should also be most likely very versatile for use in a wide variety of systems, the ART27A is a just as accomplished in every imaginable respect as any other c-j power amplifier, with added bonuses for a very, very high degree of detail, articulation and transparency with absolutely no loss of the traditional and ever improving c-j musicality magic. Even without enough power for some, the ART27A is very much a justified resident of the new reference standard department within the c-i pyramid.

That all being said, the question of components in front of and behind the ART27A is a pressing one. You don’t use a reference standard preamplifier with baseline and entry-level components, and the conrad-johnson power amplifier is sufficiently resolving to insist on the best. There is a natural partner in the conrad-johnson GAT S2 line preamplifier, of course, but to get the most out of this power amplifier you need to be willing to use a product with that kind of performance abilities. You could make a similar assumption about source components, cables and equipment supports; this product delivers a top-notch performance and demands the same of the components to which it connects. 

 

Loudspeakers are a more complex question here. That limited power output does suggest the use of loudspeakers with a relatively high efficiency, but in many contexts it’s that first watt that is the most important and all else from there is icing on the cake. However, the reality is there are some loudspeakers with notionally easy driving capabilities that have nasty impedance dips that are more likely to challenge a lower-powered valve amplifier. Granted, the ART27A is better equipped than most to handle this, but the strictures imposed by the technology mean more care in speaker selection. I admit that I was extremely shocked – in a good way – in terms of just how far you were able to push the ART27A with loudspeakers that shouldn’t be a match with a relatively low-powered amplifier, so long as you stay within reasonable loudness limits. 

The question on people’s lips will always be ‘which one is best?’ but in fact it’s a false dichotomy at best. The ART300 and ART27A play to different strengths, work with different systems (especially in terms of loudspeakers and room, even if there is a lot of wiggle room on the part of the ART27A). The simple answer to the question is ‘yes’ or ‘they are both better than each other’. There is no set answer here. Both are outstanding in their own different ways and while there is a lot of crossover in terms of tonality and frequency extension. It’s much more than one has authority, the other has a sense of musical grace, just as it’s wrong to think one is for rock listeners and the other is for jazz fans. The truth is, you should listen to both, and then decide.

In very real terms, the conrad-johnson ART27A is a bit of a revelation. In fact, it’s several revelations rolled into one. It shows just how powerful a low-power amplifier can be in reality. It shows just what happens when a brand with a well-deserved reputation for making push-pull amplifiers turns its hand to single-ended designs. It shows in a world that has adopted the KT150, there is still lots of mileage in classic valves like the KT88, and it shows there is a lot of merit in thinking just a little bit out of the box. The end result is something of a ground-breaker for c-j. 

Somehow, I think the ART27A is not simply a limited-run amplifier; I think it’s the start of something in conrad-johnson. While I don’t think the brand – or its followers – are going to switch over from push-pull designs en masseany day soon, I can see a time soon where conrad-johnson may have both push-pull and single-ended amplifiers side by side in its line-up. I guess whether or not that happens depends on the popularity of the ART27A. Judging by its performance, I’d really love to see more designs like this one. 

TECHNICAL SPECIFICATIONS

Type: Triode-coupled Class A valve stereo power amplifier

Inputs: 1× pair single-ended RCA stereo line-level inputs

Outputs: 1× pair multi-way loudspeaker terminals (4Ω output) 

Tube complement: 3× 6922, 4× KT88 (matched pairs per channel)

Frequency response: 20Hz–20kHz ± 0.25dB

Power output: 36W (from 30Hz–15kHz, at no more than 1.5% THD into 4Ω, 8Ω and 16Ω taps available)

Hum and noise: 108db below rated power

Dimensions (W×D×H): 48.3 × 44.5 × 22.2cm 

Weight: 28kg 

Price: £24,500

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

Tags: FEATURED

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