This blogpost on the Leben CS-600 and the Leben CS-600X tube-based amplifiers started out as a thorough introduction to vintage tubes after buying a Leben CS-600 a couple of months ago.
From there, it branched out to cover additional amplifiers from Leben Hi-Fi Stereo Company; from their early models to their latest offerings of tube-based products with a special focus on the integrated amplifier designs.
Summary: What Makes the Leben CS-600 Great?
- Excellent build quality – I had expected a lot, but got even more – heaviness, solidity, finish, smoothness and precision of knobs
- Aesthetically top-notch (but a preference if one likes the design)
- Dead silent background irrespective of input sources
- Sufficient inputs
- Possibility of adding a dedicated preamplifier through the ‘pre-amp in’ inputs
- Tape out – which I use to connect an USB sound card to do sampling of vinyl records with (with the RS30-EQ)
- High resale value. The CS-600X costs around the double I paid for my CS-600.
- Balance and bass boost (not something I use)
- Headphones out
- Compatible with a wide range of output tubes
- 6CS7 input tubes very reasonably priced when I got it
- Sufficient watts output for a wide range of speakers (28 watts with EL34 family and 32 watts with 6L6 family of output tubes
- Heavy transformers to back the watts up
- Wide range of impedance settings to match different speakers
- Possibility of by-passing several circuits using the tape in connections
- Stability – I’ve had absolute no issues with it
- Differences between the Leben CS-600 & CS-600X
Also see: Copenhagen Photographer ~ Kasper Bergholt Photography
Input & output tubes in the Leben CS-600 vs CS-600X
Both the Leben CS-600 & CS-600X have four driver tubes facing the listener – behind these are four output tubes. In the driver stage of the CS-600X there are two 12AU7A and two 12BH7A tubes; in the Leben CS-600 all driver tubes are of the 6CS7 variety.
In the CS-600X the distribution of driver/preamp tubes is: 12AU7A; 12HB7A; 12AU7A and 12BH7A.
In addition, there’s a C6J3 damper tube in the CS-600 and a 6CM3/6DN3 damper tube in the CS-600X.
A word of warning on changing tubes
From the Leben CS-600 manual: “Before removing a top cover for replacing tubes, please confirm the power cable is disconnected and the tubes are cooled down”.
Yoshi Hontani’s inputs on tube placements
I’ve corresponded with Yoshi Hontani, Leben’s Japanese distributor and general contact facing the English-speaking world, who described tube positions this way: The two left tubes are for left channel; and two right tubes are for right channel.
This gives us: Tube 1 (from left) is first stage for left channel; Tube 2 (from left) is second stage for left channel; Tube 3 (from left) is first stage for right channel; Tube 4 (from left) is second stage for right channel;
The selection of driver tubes for the CS-600X is a lot wider, offering both the option of NOS (New Old Stock) tubes and modern productions. Many seem to prefer the sonic signature of the older brother for being more transparent, precise, airy with a wide sound stage, whereas the CS-600X is more lush, warm and what could be termed tube-like in character.
Another difference between the two is the choice of damper tube used in the amplifier design. One uses a C6J3 damper tube, while the other uses a 6DN3 damper tube.
Tube upgrade set for Leben CS-600
Bypassing the input selector in the 600 & 600X
In a recent review of the CS-600X it’s suggested to use the tape-in input to bypass the input selector for improved sound by a shorter signal chain:
“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!”
In a setup of this character, taking the price of the amplifier into consideration, I thought it wise to ask Leben directly if this was a safe and recommended way of connecting things.
“In a recent review in (Stereonet) it’s suggested to use the tape-in input to bypass the input selector for better sound, see below. Is this considered safe / beneficial use of the function if no recording device is connected to the tape-out?
Yoshi Hontani replied quickly:
“Yes, this is true. You can use the TAPE MONITOR directly to receive a Phono input (for example).”
I’ll have to do some comparative listening sessions to see if 1) I can hear any difference; 2) the differences being to the better.
On tube-rolling / tweaking: Blessing and curse
Of course these characteristics change with different tube combinations, and that’s one of the charms that attract some people to tube amplifiers. Over time our hearing can change, our preferences change, our speakers can change, our RIAAs and DACs, the synergy of which can be tuned by different choices of preamplifier and driver tubes.
Admittedly, this can also be a curse, an ongoing tweaking and split testing resulting in an over-emphasis on the voicing of the amplifier at the cost of the listening experience.
In a sense, I think Leben’s motto ‘A Motion Sound’ is an attempt to transcends the more analytical layers of the Hi-Fi experience – it’s my experience that most reflections on the contents of movies come before and after the viewing experience.
Supplies of 6CS7 tubes have dried up lately
The supply of NOS (New Old Stock) 6CS7 tubes has quickly depleted during the last couple of years. “The Tube Store”, the American reseller of vacuum tubes has addressed this issue on their website, providing a notice stating that their supply is extremely limited in comparison to earlier, and as a result they are no longer able to offer matched pairs or quads of 6CS7s:
“Note to Leben [CS-600] amplifier owners, we do not have matched sets at this time. These tubes are very difficult to find. Only odds and ends of various brands available,” The Tube Store, August, 2023.
In general this phenomenon is called “Vacuum Tube Extinction” and is something one should be aware of when investing in a tube amplifier.
The CS-600X manual has section on why 12AU7A and 12BH7A tubes were chosen for the new first stage of amplification:
A huge quantity of these tubes (12AU7A and 12BH7A) were produced by many manufacturers in the past and many high quality NOS tubes are available on market, therefore, you have a chance to try several different NOS tubes by replacement. Apart from it, these tubes are still being produced for musical instruments and also for audio amplifiers, and there is no fear of replacement tubes in future as well.
To sum up, only 6CS7 tubes can be used in the CS-600 – and only 12AU7A (ECC82) and 12BH7A tubes can be used in the CS-600X.
Description of the circuitry in the CS-600X from the CS-600X manual
After the first stage amplification by SRPP through the first triode unit of 12AU7A and 12BH7A, make a phase reverse by Mullard type cathode connection through the second triode units, then transmit to the last stage.
Self-biasing circuit(Auto-biasing circuit) will protect the output tubes EL34(or 6L6) from damages from age. A characteristic of the damper tube(6CM3/6DN3) is to rise a high voltage gradually, which will affect very much to extend a life of the output tubes.(6DW4B also can take place of 6CJ3). The Bass Booster of CS600X is controlled by capacitors arranged on the “NFB loop”, that is a very rare method. Bass(or treble) control is
normally controlled by a tone control circuit, however, the above method makes the circuit much more simple.
Further more, in order to cut a negative influence of the Bass booster to the middle frequency, 15Kohm resistor(filter) is arranged in the circuit.
Leben CS-600 factory specifications
Tubes employed:
4 X 6L6GC (5881) (output tubes)
4 X 6CS7 (input / driver tubes)
1 X 6CJ3 (6CM3)
Output power: 32W X 2 (6L6GC)
1KHz. Frequency response: 10Hz – 100KHz (-0.1 dB)
T.H.D: 0.7% -(1KHz/10W)
Input sensitivity: 900mV at 20W
Output impedance: 4/6/8/16 ohm (selectable)
Headphone output: 1000mW Power consumption: 195W (Max.)
Dimensions/size: 450(W) X 360 (D) X 142 (H) mm
Weight: 22.5 kilos.
As far as I know, there hasn’t been any changes to these specifications.
Tube settings table / overview of output tubes
6L6, KT77, &L&GB, 350B, KT66, KT88, 6550A
There is a wide selection of tubes currently in production from different manufacturers. In addition to the 6L6/5881 and EL34, the both amplifiers are compatible with KT77, 6L6GB, 350B, KT66, KT88 and 6550A tubes.
Some of the tubes are considerable taller than the classic 6L6/5881 & EL34, so the lid cannot be on when operating those. In that way, the design accommodates both tube collectors who were lucky (or clever) to buy NOS tubes when the prices were at a completely different level from what they are now for the best tubes from the best brands.
C6J3 damper tubes in Leben amplifiers
The Leben CS-600 and the Leben CS-600X both employ so-called damper tubes in their designs. The CS-600 utilizes a C6J3 tube, and the CS-600X uses a 6CM3.
EL34 RFT tubes including measurements on Roetest V10 tester
My first experiment with another type of output tubes is four New Old Stock EL34 tubes by the German manufacturer RFT marked ‘Philips’. The tubes are now on their way to me from Croatia.
Testing them out is a project for the near future. RFT stands for Rundfunk- und Fernmelde-Technik. Below are the measurement for each EL34 tube performed by a professional on a Roetest V10 tube tester. I’m looking my forward to listening to these and compare them to the stock 6lL Sovtek tubes the amplifier came with from the factory.
Current setup
Leben CS-600: Sylvania 6CS7 tubes, black plates (New Old Stock) + Russian 6P3S-E output tubes (Reflector, New Old stock). 6CJ3 damper tube.
Speakers: Harbeth M30.1
Tonearm cable: Yannis Tomé Audio Cables, Silvercord Duo 24, silver
Interconnect: Yannis Tomé Audio Cables, Clio, silver
RIAA: Leben RS30-EQ RIIA (Hytron 6X5GT rectifier tube + two Telefunken ECC81s)
Turntable: Project X2, with upgraded RCA connectors
Cartridge: Goldring 2400
Speaker cables: Duelund speaker cables, solid-core copper in cotton and linseed oil.
A Short History of Japanese Leben Hi-Fi Stereo Company
Leben Hi-Fi Stereo Company, established in 1995, is a Japanese manufacturer of high-end tube-based pre-amplifiers, power amplifiers & integrated amplifiers, and, so far, a single tube-based RIAA, the Leben RS30-EQ.
Leben is a German loan-word that translates into ‘to live’, ‘to be alive’, ‘lively’ or simply ‘to exist’. Newer models contain the tag-line ‘A motion sound‘ adding a feeling of experiencing music in a Haruki Murakami-like atmosphere.
Taku Hyodo, Leben’s fonder
Mr. Taku Hyodo, an experienced audio engineer with a past working for Luxman, is a collector of new old stock vacuum tubes, for example 6X5GT, 3CSS, 12AT7, E288CC and 6L6GCs, in addition to being a music lover with a professional back ground playing the guitar.
At 60, Mr. Taku Hyodo left Luxman in 1979 to establish hs own company, “Kouri Denki Corporation”. He kept designing and constructing amplifiers under the ‘KFH’ brand name – primarily custom-made products for café, bars and restaurants, also a somewhat Haruki Murakami-like project.
The first product to see the market, the ‘Triode 33’
Mr. Taku Hyodo’s first commercial product to see a broader market was the ‘Triode 33’ power amplifier released in 1991 followed by the RS-35A 6L6GC tube-based power amplifier under the Leben brand in 1995.
Leben released the RS-28C preamplifier (equipped with E288CC tubes) in 1998. To cater to a wider range of audiophiles, Leben subsequently introduced a series of more affordable amplifiers: the CS-200, CS-250, CS-300, and CS-300X, released in 2001, 2002, 2003, and 2005, respectively.
Broader access to the products from Leben
These amplifiers allowed a broader audience to experience the unique sound quality associated with Leben products.
In 2005 Leben released the Leben CS-600 amplifier featuring four 6CS7 tubes for the driver stage and four 5881 or EL34 output tubes.
The CS-600 was succeeded by the CS-600X in 2019, with the design remaining mostly the same, except for the type of driver tubes.
Point-to-point wired tube amplifiers are rarely seen nowadays, as they requires a skill set few modern workers have in world af general mass production.
Leben is one of few amplifier manufacturers that feature amplifier designs of this type thanks to a highly skilled number of employees working in the company’s quarters in Nishi-Koya in Amagasi City, Japan.
Also see:
Objects for an Ideal Home