The Leben CS600x will shatter your preconceptions of what an EL34 integrated amp sounds like. It is one of the most musical pieces of gear I’ve ever owned, and it combines the best qualities of SET and ultra linear tube amps. Reward it with NOS line stage tubes and upgraded power tubes, and it will produce exceptional sounds.
I am no stranger to tube amps generally, or EL34 amps specifically. I’ve owned many EL34 integrateds, including the ASL DT1006, the VAC Avatar SE, and the Conrad Johnson CAV50. I’ve also owned the mighty AirTight ATM3 monoblock amps (six EL34’s per channel) and the lowly Dynaco ST70. For headphone, I started with the Woo WA6SE, and graduated to the Woo WA22 and WA5, the latter two of which I still own.
I was intrigued by the Leben after reading about its synergy with Devore Fidelity speakers, and also the magic of the Leben CS300 as a headphone amp. My mighty Woo WA5 is tough to beat with headphones and does a stellar job with very efficient speakers but I was searching for a bit more power for the speakers. The waiting time to procure a 600x was nearly six months, and they are rare as hens teeth on the used market. The earlier 600 model can be found, and can be upgraded to the X, but it uses different line stage tubes that are becoming harder to source, as there is no new production and the NOS versions are spendy, hence the x model, whose tubes are easily sourced.
After a week of burning in, the 600x founds its true voice. On recommendation, I swapped the EH EL34 for the Gold Lion KT77s, and experimented with several NOS line stage tubes before settling on a pair of Sylvania and CBS tubes, with GE, Raytheon, and RCA tubes faring quite well too. Tube swapping noticeably removed some grit and glare present in the JJ new production tubes.
The Woo WA5 is a splendid SET amp, and the 300b creates a believable immediacy that is truly beguiling. I was expecting to lose this in return for better dynamics but the Leben surprised me. It had palpable body and presence, if not quite as present as the 300b amp, it was darn close. The soundstage was more lifelike, and inner detail of brushed cymbals, the blat of horns, the decay of percussion, and the placement of instruments was exceptional. I’ve never heard an EL34 amp sound this transparent, and it managed to give detail, immediacy, and dynamics without sacrificing warmth and tone. It completely rewrote my understanding of what a great EL34 amp can be. It has the presence and palpability of a SET amp, but with the dynamics I typically associate with 6550 or KT88 tubes. And it doesn’t lose the warmth and overall pace of the EL34, but rather improves on the usual rounded sound in surprising ways. Bass is never rock solid but is far more firm than any EL34 amp I’ve experienced, and the top end is crystal clear but still warm. Definitely confounds my stereotypes of the EL34.
This was the experience with loudspeakers. With headphones, the Leben 600x was wonderful but the quality of results depended a bit more on the headphones. The LCD3 and HD650 were really terrific, if not perhaps as fully dynamic and manhandled the way they sounded on the mighty Woo WA5. While I ultimately preferred the WA5 on these two headphones, I could be quite happy with the Leben, which excelled over the WA22 except perhaps with the HD650 (which in balanced mode with a balanced source, mates exceptionally well with the WA22). With the Focal Clear, the Leben was less successful than the Woo WA5, and not as equal to the WA22. The bass was a bit soft, and the sound was less dynamic than the Clears can produce. I suspect it has something to do with Clear’s very low impedance and matching with the Leben, but either way, it didn’t knock me over the way the WA5 did on the Clear. The LCD3 was just right with the Leben, showing firm tight bass, delicious midrange, and clear musical top end. The WA5 only bested the Leben by giving the LCD more energy and bounce.
Judged purely as a speaker integrated amp, I have to absolutely side with the Leben. It does everything the WA5 does and more - more dynamics, more soundstage height and depth, more detail, and more effortless presentation.
Judged as purely a headphone amp, I’d still have to give the nod to the WA5, but not necessarily to the WA22 - it depends on the headphone. For an integrated amp that needs to double as a headphone amp, however, the Leben takes the clear win. It’s very versatile and it’s a clear keeper.
For now, the WA5 still stays but I’m looking hard at justifying keeping the WA22 because it only does headphones, and it only betters the others on the HD650 and Clear when running in full balanced mode. But the Leben will now occupy the place of honor in the main system, and it continues to enchant. That it also looks marvelous and will last a lifetime is a bonus.
