Leben CS600X Integrated Valve Amp Review

Posted on 6th February, 2023
Leben CS600X Integrated Valve Amp Review

James Michael Hughes warms to this exclusive high-end Japanese tube amplifier…

Leben

CS600X Integrated Amplifier

USD $8,995 | CAD $12,995

Leben CS600X Review

Leben is a small specialist Japanese company that has been hand-building high-quality tube amplifiers since 1992. Founded by ex-Luxman engineer Taku Hyoda, it approaches design and manufacturing in a very traditional and conservative manner – one that hearkens back to hi-fi's fabled golden age. Indeed, even if the CS600X had been introduced back in the late nineteen sixties, its styling could have been judged staid and old-fashioned! Those wooden end-cheeks made from Canadian ash may strike today's audio fashionistas as somewhat dated, but to me, it looks classic.

Construction is very sturdy, as the amplifier weighs around 23kg. The knobs, made from solid alloy, turn with smoothly satisfying gravitas. The volume control feels nicely damped and has gentle indent points that facilitate precise, repeatable settings. Taking the retro approach to near hairshirt extremes, Leben even eschews infra-red remote volume adjustment – it's simply not offered! So in almost every way, the CS600X is exactly like an amplifier that might have been made forty or fifty years ago…

Leben doesn't introduce new models very often. The original CS600 was released as far back as 2005, and the CS600X, which replaces it dates from 2019. Why the change? Difficulty obtaining supplies of NOS (New Old Stock) 6CS7 tubes used in the earlier design, apparently. As a result, the circuits were modified so that 12AU7A and 12BH7A tubes could be used in place of a single 6CS7. Fortuitously, this allows CS600X owners to experiment with readily available NOS 12AU7A and 12BH7A tubes for a more vintage sound.

Leben CS600X Review

The amp is supplied with four EL34 output tubes as standard, giving a claimed 28W output, but 6L6 tubes (giving 32W) can be had too. Other output tubes – KT-66/77/88 – and 6550As may also be used. To facilitate this, the CS600X is equipped with a couple of internal switches to alter the anode voltage from 410V to 450V, with a choice of 460-ohm or 680-ohm cathode resistors. The option selected is usefully indicated by LEDs on the front panel. The amp also features anti-vibration support feet, as used on Leben's CS1000P model.

Point-to-point wiring features internally and – as befits a proper traditional tube amplifier – the power supply features a glowing glass bottle rather than solid-state devices. A NOS 6DN3 rectifier tube is employed, with a large 5 Henry smoothing choke to reduce ripple. Leben winds all its transformers and chokes in-house at the factory; this is important as transformer quality is critical with tube amps.

For optimum loudspeaker matching, the CS600X offers a choice of 4, 6, 8, and 16 ohm impedance taps via a switch on the back. Subjectively, the 'correct' impedance is usually the one that sounds loudest since this indicates the most efficient transfer of energy. Choosing a lower impedance value than that of your speaker can sometimes enhance firmness and control; however, so by all means, experiment…

Leben CS600X Review

Maximum mains power consumption is around 195W; the amp runs in Class AB rather than pure Class A. During use, it gets fairly warm but not uncomfortably hot. I measured temperatures of 41C right above the 6DN3, with 35C at the centre of the top plate and 29C near the front. It's very quiet mechanically and electronically, with virtually no transformer buzz, residual hum or hiss, even using very efficient speakers. While the CS600X does not feature tone controls, or scratch and rumble filters, it does have a switch that boosts bass by 3dB or 5dB.

Also fitted is the usual left/right balance control, plus a stereo-reverse switch that swaps left/right channels; I'd have liked a mono option too, but alas, that wasn't included. Another feature from yesteryear is a tape monitor loop for three-head open reel or cassette decks.

THE LISTENING

The CS600X gives a very lucid, well-resolved sound that's tactile and immediate, and deliciously smooth and refined. There's also a fullness and weight that epitomises what many think of as the traditional 'valve amp sound'. At the same time, this amplifier is impressively clean and focused. It is detailed, balanced and cohesive without being overly euphonic.

Playing Otto Klemperer's Beethoven Eroica Symphony from 1959, I liked the ripeness of the reproduction and its lack of congestion. Having known Klemperer's Beethoven cycle for over fifty years, on LP and CD, I've always found these recordings difficult to reproduce. There's a thinness/harshness that's difficult to eliminate, needing something like the high-frequency filtering system found on Quad's old 33 preamp. Yet the CS600X reproduced this old and slightly threadbare recording in a surprisingly clean and full-bodied manner.

Leben CS600X Review
 
Subjectively, it was like taking ten years off its age. I immediately felt very comfortable listening to the Leben. Sonically, you could liken it to a pair of comfy old shoes that fit so perfectly that you forget you're wearing them – but don't just assume that means soft, warm and mushy. This amp is refined, clean, and focused – but also impressively tactile and assertive when the music demands it.

I found it devastatingly good on solo piano. Playing the late Nelson Freire's Decca album Brasileiro, the CS600X highlighted his superb articulation and command of dynamic nuances, along with his myriad shifts of tone colour and subtle expressive rubato. Amazing! Piano tone had plenty of 'ping', but more satisfying was the sense of weight and richness that gave the instrument an impressively solid and full-bodied middle and low register. Yet the CS600X never drew attention to itself but simply gave you the music without getting in the way.

Like all good valve amps, the sound is gutsier and more powerful than the specs suggest. I was using sensitive Klipsch Cornwall IVs (around 102dB efficient), so these speakers made the most of what the CS600X had to offer. Just prior to getting the Leben, I'd gone back to using my old EAR 859, which I bought about twenty-five years ago. Despite just 13W output, it sounds surprisingly powerful. The EAR 859 artfully disguises its distress when pushed beyond its power envelope, and the CS600X behaves in a similar fashion.

Leben CS600X Review

Driven hard, both amps just compress very gently, so you're hardly aware that the outer limits have been reached – but much depends on the music. I find natural uncompressed recordings of choral music and unamplified human voice challenge low-powered amps the most. Conversely, many rock/pop albums are highly compressed to sound loud, forward and superficially dynamic – but there are no unexpected peaks to tip the amplifier out of its comfort zone. A simple uncompressed solo soprano voice is far more demanding!

Vocals – both classical and pop/rock – sounded full and very 'present', yet backing voices and instruments were never swamped and always came through clearly. I really noticed this playing Emmylou Harris's moving rendition of The Beatles' For No One. While the CS600X has approximately twice the power of the EAR 859, those extra watts only equate to about 3dB more level. What's important is that the Leben, like the EAR, sounds 'big' and is good at disguising its limitations in terms of power restrictions. It rarely sounds stretched.

The CS600X's crisp pace and timing produced very cohesive results. On Thallein – a difficult, awkward knotty piece by Greek composer Iannis Xenakis – every rhythmic turn and unpredictable dynamic shift was clarified and structured to create a coherent sense of ebb and flow. As a result, Xenakis's strange and hard-to-follow music made sense. I noticed time and again how clearly and precisely the CS600X was able to define the pitch of notes, along with the timbre and texture of individual voices and instruments. This made the music clearer and easier to follow.

Bass was full and warm. Maybe there isn't quite the tautness and vice-like control of some really good solid-state designs, yet neither is the bass soft or flabby – just rounder and fuller. I didn't need to use the bass lift feature, but it could be useful for small speakers. Incidentally, you'll get better sound from the CS600X using the tape monitor input rather than the regular line inputs. Why? Because the tape monitor bypasses the main selector, resulting in a shorter more direct signal path. Try it!

Leben CS600X Review

While the EAR 859 comparisons were interesting, a more telling challenge was provided by the Technics SU-R1000. It's an advanced high-tech integrated amp boasting the latest in modern technology. It also has a built-in DAC and an excellent MM/MC phono stage. Unusually, its 150W power amp employs digital technology to combat real-world technical issues an amplifier faces when driving loudspeakers. If the CS600X could have been made half a century ago, the SU-R1000 could only have been created in the last few years…

The Technics gave a drier and more immediate sound with greater attack and a heightened sense of control. Its presentation was akin to moving ten or fifteen rows forward in the hall, compared to the Leben's spacious, relaxed, and darker, more subtly nuanced presentation. The SU-R1000 delivered impressive immediacy, with power to spare, but wasn't nearly as graceful and flowing as the CS600X. On Art Pepper Meets the Rhythm Section, the mellifluous velvety smoothness and rich, mellow sonority of Pepper's sax was beautifully portrayed by the Leben. Its easy charm convincingly conveyed the sonic impression of real acoustic instruments playing in a clearly defined space. The music flowed effortlessly with a relaxed ease and sweetness, yet without loss of bite.

THE VERDICT

As you may have noticed, I find myself rather smitten with Leben's DC600X integrated amplifier and class it as among the nicest, most truthful and authentic sounding amplifiers I have ever heard. Sure, it is expensive, quirky, has no phono stage, no DAC, limited power and no remote volume control – but that's what you get when you buy a true purist product. But trust me, the sound it delivers is absolutely drop-dead gorgeous.

Visit Leben for more information

James Michael Hughes's avatar

James Michael Hughes

An avid audiophile for many decades, Jimmy has been writing about hi-fi since 1980 in a host of British magazines, from What Hi-Fi to Hi-Fi Choice. Based in London, England, he’s one of the UK’s most prolific record and CD collectors – no streaming service can yet match his amazing music collection!

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Tags: leben 

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