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The Leben CS600 Integrated Amplifier
Hyodo San told me that during the design phase of the CS600, he used the same design criteria as for the CS300 series integrateds - a simple push-pull circuit based on good tubes supported by high quality electronic components to give a total musical balance. Hyodo San made the decision to run all tubes very conservatively so they would provide extra-long life and reliability to the owner, even though it meant sacrificing some output power to do so.

For the first stage of amplification, the CS600 uses a television tube known for reliability from the black and white days, the twin-triode 6CS7, whose controlled heater provides gradual warm-up for greater reliability and extended tube life. For a rectifier the CS600 uses an ultra-reliable B&W television tube, the 6CJ3. The 6CJ3 rectifier draws little current and provides a slow turn-on of the high B-voltage to the power tubes which increases their reliability and life-span. The CS600 ships stock with Sovteks.

Only one push-pull pair of power tubes is used per channel, the conceptual equivalent of a 'single-ended' circuit in simplicity. Hyodo San feels this design provides the best combination of sonics and musicality. I think it will come as a bit of a shock to SET devotees (it did me) that this refined little push-pull integrated can go toe-to-toe in a slugfest with an SET amp and KO it musically. It's a truly brilliant design. The circuit in the CS600 is self-biasing to give the music lover a carefree product - plug'n'play as they say in computer circles. There is a blue LED above the volume control that will light up a few seconds after the CS600 is turned on to indicate that it is ready to play music. The blue LED is powered by the output tube cathode bias and not by a relay or timer, meaning the LED lights only when the output tubes are fully warmed up and ready to go.

There are cathode-resistor and plate-voltage switches inside the chassis to optimize the CS600 for a variety of different tubes should you want to experiment with voicing the amplifier for a particular system or a bit of tube rolling fun. I found this feature quite helpful in the review of the ASA Monitor Baby loudspeakers to get the best sound from them. I replaced the stock 6L6GC tubes with EL34 tubes to add a little needed warmth to the ASA's pro-monitor balance. With the warmer and darker Harbeth Super HL5s, I found the more neutral 6L6GCs to provide the best overall match. With 6L6GC tubes in place, the CS600 provides 32 watts, 28 watts with the EL34. There are red and green LEDs above the power switch that will light up to show if you are using 6L6GCs or EL34s respectively.

There are many other tube choices for extra entertainment. The CS600 can run a variety of tubes from the 6L6 and EL34 families by varying the positions of the cathode & plate switches. In the 6L6 family, there are the aforementioned 6L6GC, the 6L6WGB, the 6L6GB, the KT66 and the 350B. In the EL34 family the there is the EL34 and the KT77. In addition 6550 and KT88 tubes (ditto for the 350B) can be used if you leave the top cover off to allow for the tubes taller height. It would be nice if there were some circular vent holes in the top cover so you could leave it in place with the taller tubes. For a truly excellent discussion of tubes that are compatible with the CS600, how to set the position of the switches for each type, and some tips on choosing some extra-special NOS tubes for your CS600, visit the Soundscape Hi-Fi website. For another good read, check out Watford Valves test report for the different EL34 and 6L6GC tubes.

The CS600 has an input for a preamplifier that allows it to be used as a power amplifier, bypassing the source selector, mode switch, tape monitoring circuit and volume control. The CS600 also has a headphone jack where the audio signal from the output transformers is taped directly. I've been told by several people that the headphone performance of the CS600 is out of this world but not being a headphone kind of guy, I haven't checked it out for myself yet. I'll try to follow up on that in the future and let you know my thoughts.

The CS600 has a two-position bass boost circuit (+ 3dB and +6dB) that I found to be useful in nicely fattening up the bottom end of lean speakers like Fostex single-driver models to make them sound a little more natural. The bass boost is controlled by condensers and resisters located in a negative feedback loop, a very rare and refined method I'm told since bass boost is normally controlled by a tone control circuit. However, Leben says its way of doing it makes the circuit far more simple and effective. The midrange is shielded from the bass boost circuit by a 15Kohm filter resistor within the circuit.

The Harbeth loudspeaker company came into being back in 1977 when Dudley Harwood, a member and leader of the BBC's research team in acoustics, retired from the BBC in order to manufacture loudspeakers utilizing his research ideas of incorporating polypropylene into the cones of the mid/woofer. Dudley named his new company Harbeth, which is a contraction of Harwood, Dudley's last name, and Elizabeth, his wife's first name. Dudley's research had shown that polypropylene was superior to the more commonly used bextrene cones of the day so he manufactured a loudspeaker to prove his point. As a result the original Harbeth HL Monitor was born and with it the world's first loudspeaker to use polypropylene as a cone material. In time polypropylene would displace bextrene and become a standard for cone material due to its excellent performance, lighter weight, higher reliability and lower manufacturing cost.

Alan Shaw's involvement with Harbeth followed a chance encounter with Dudley Harwood in the spring of 1986, about which Alan says, "it's a long story but in essence, I'd been avidly following the BBC speaker philosophy since my teens and Harwood, Shorter and Hughes had been (and still are) heroes ... I was certain that destiny had brought us together." Dudley made it clear to Alan that he wished to retire being about 70 years old at the time. He told Alan that he was entirely on his own with his dreams for Harbeth. Alan said, "That was the best legacy that he could possibly have given me because it forced me to hit the ground running." Alan resigned from the position he held at NEC where he was responsible for their semiconductor business, to focus on his vision for Harbeth.

Alan began his tenure at Harbeth and continued with the BBC's loudspeaker legacy by making progressive detail improvements over time, like the RADIAL (Research And Development In Advanced Loudspeakers) cone material. The RADIAL uses a polymer formulation unique to Harbeth, which Alan developed and patented with assistance from the British Government's Science & Engineering Research Council (SERC).

Alan says Harbeths are expensive to manufacture due to the expense of developing and manufacturing the RADIAL drivers and because of the high cost associated with building the thin-wall BBC-style cabinets. These labor intensive cabinets use five damped and tuned sub-system panels that are voiced much like a musical instrument to achieve the signature Harbeth sound. Alan says that "the 'thin-wall' box concept was thoroughly researched by Harbeth's founder at the BBC and we've stuck with it because it works despite the high cost and difficulty of assembly from individual wood panels."

Harbeth's primary customer in the UK, aside from devoted music lovers, is the BBC who uses active and passive versions of the Monitor 20, 30 and 40 in their television and radio stations. But it isn't just in the UK that Harbeth enjoys notoriety. Alan has seen an enormous increase in orders from discriminating music lovers in Japan and the Far East. In fact, the Japanese magazine Stereo
Sound recently voted the new ES3 version of the Harbeth HL Compact 7 as the best speaker in its class - a very prestigious award.

Some years back Walter Swanbon of Fidelis Audio-Visual showed the Harbeth Super HL5 and Monitor 30 loudspeakers he imports with Art Audio electronics at T.H.E. Show in Las Vegas. I was blown away by the rich musicality and natural-sounding sonics of the pairing and have never forgotten the experience. Following up I reviewed the Monitor 30s and have been blabbering about Harbeths to my audio pals ever since. When it came time for a reference loudspeaker for the Music Lovers series, the first thing to mind was Harbeth so I placed an order for a pair of Super HL5s in the striking Tiger Ebony finish.

Walter told me that a number of his customers have asked him which of the identically priced Super HL5 and Monitor 30 I liked best since I had experience with both. Here's the answer from the horse's, ahem, mouth: It depends on the room. It's as simple as that. In a smaller room like my 11' x 11' study, I prefer the Monitor 30 but in a larger room like my 20' x 17' living room, I like the Super HL5 best. Either way you can't go wrong with a pair of Harbeths. They're one of the most musical speaker lines ever developed and an easy recommendation for music lovers everywhere.

Walter imports the following Harbeth models to the USA. The diminutive HL P3ES-2 sells for $1850 in Cherry, $2099 in Eucalyptus and $2150 in Tiger Ebony. Next in the lineup and larger than the P3ES-2 is the newly released ES-3 version of the HL Compact 7. It's $2999 in Cherry, $3299 in Eucalyptus and $3499 in Tiger Ebony. The Super HL5 adds a supertweeter and a larger enclosure and is priced identically to the smaller Monitor 30 at $4299 in Cherry, $4399 in Eucalyptus and $4599 in Tiger Ebony. The largest Harbeth is the Monitor 40 which weighs in at a hefty $9999 in Cherry, $10299 in Eucalyptus and is available by special order in Tiger Ebony.

Harbeth Super HL5
Remember that original Harbeth HL monitor that was launched by Dudley Harwood in 1977? The Super HL5 is the sixth generation of that original Harbeth, still using what is essentially the same size veneered birch ply 25-inch high x 13-inch wide x 12-inch deep cabinet, giving it the deepest roots into Harbeth history of any model in the current product line. This year -- 2007 -- is in fact the 30th anniversary of that revered HL monitor.
That first HL (the Mk1) used an Audax tweeter and polypropylene woofer to give a 50Hz to 25kHz range. The Mk1 through Mk3 versions of the HL monitor were quite similar, using the same tweeter with only some small detail improvements to the bass driver, crossover and grill. The Mk4 version of the HL was the first major change to the design, going from the original polypropylene bass/mid driver to an Audax TPX. The 5th generation of the HL, now called the HL5 (instead of being referred to as the Mk5), continued to refine the design with a removable baffle, a SEAS tweeter and a different bass/mid driver (first an Audax/Harbeth hybrid design, then the RADIAL design in subsequent productions).

Now in the 6th generation, the HL5 adds a supertweeter which garners it the 'Super' HL5 designation. The driver complement for the Super HL5 is thus the Harbeth-made 200mm RADIAL bass driver, a custom SEAS 25mm aluminum dome tweeter and a SEAS 20mm titanium dome supertweeter. The RADIAL driver increases low frequency extension by an extra 10 cycles to 40Hz and the supertweeter gives more extension on top to take advantage of analog and the newer digital formats like SACD. Harbeth specs the Super HL5 from 40Hz to 24kHz (± 3dB in free space), but the supertweeter actually goes north of 96kHz. In practice, I found that in my listening room I was getting significant audible response from my Super HL5 down to 20Hz using the Stereophile test CD. Harbeth gives a sensitivity rating of 86dB 1W/1m but the Super HL5 is a much, much easier load due to its excellent design than the sensitivity spec would suggest. Harbeth recommends an amplifier with 25 watts or more to power the Super HL5 [Compact 7 to right].

The cabinet is 60 liters in size and is built using tuned thin-wall birch ply panels as is customary with BBC monitor designs. The front and rear panels are attached with 12 brass screws each that are torqued to a specific value to tune the cabinets. The crossover is reasonably complex and uses 27 components soldered to a fiberglass printed circuit board. There's a really nice discussion about the "four key functions" of a Harbeth crossover on their website that will give you the full story. The Super HL5 is set up with two pairs of binding posts for bi-wiring. I'd much rather see one set of binding posts personally though I'm probably the minority here.
The speaker grill is a fabric-covered stiff metal frame that fits into rather deep grooves on the front of the cabinet. Harbeth calls it the SuperGrille because they don't believe it affects the sound quality (it does). In my opinion the only thing super about the SuperGrille is that it's a super pain in the arse to remove and more than one Harbeth owner has permanently damaged their speakers trying to do so. I like the sound best with the grilles removed and I think the speaker looks a lot better without them too. Here's how Alan says to remove the grilles without damaging your Harbeths:

"We are planning to make a little video but in the meantime I'd say pinch some cloth between thumb and first finger and give the grille a really good tug. Yes, sometimes they are tight but that's better than loose and buzzing and as you may know, I recommend that the grilles are left fitted for listening - counter-intuitive maybe but the response is actually smoother with them on so effective is the grille design."

There is no way I could pull off the grills by pinching them between my fingers and I have strong and grippy guitarist fingers. I had to resort to using a pair of pliers (which I covered with masking tape to protect the grille cloth and veneer in case of a slip up on my part). The trick is to grip the metal frame firmly with pliers -- be careful because the stretchy grill cloth will slip on the metal frame's surface -- and pull it straight out towards you. This will dislodge one corner of the grille, generally, and then you can pull the rest of the grille frame out of its groove by hand. Be very careful with the pliers so you don't damage any veneer and whatever you do, do not use a screwdriver to try and pry off the grill. The grill frame goes too deep into the wood to be able to get any leverage on
it and all you will accomplish is damaging the wood of the speaker around the grille. The grille is in desperate need of a redesign to be more user-friendly. A simple cloth pull tab somewhere on the metal frame that would allow you to give it a good grip for removal without having to use pliers would be a big improvement.

Skylan Manufacturing Ltd.
Located in Calgary, Alberta, Noel Nolan is Mr. Skylan and Harbeth recommends his stands for their loudspeakers. Skylan speaker stands are strong, light (until you mass load them anyways) and non-resonant. I like them a lot. Noel's stands are a combination of nicely finished MDF top and bottom platforms with little polymer bumpers on top that your speakers rest upon. The Super HL5 versions have four extruded polymer pillars between top and bottom plates for plenty of stability and mass loading. I mass load my stands with sand and use the included spikes to level them and anchor them to the floor - they work great! Noel's stands come flat-packed and are easily assembled and the package comes with all the tools you need to put them together. All you have to do is fill them up with sand after you assemble them and you're ready to go. This saves a lot of money on shipping compared to heavy metal stands, particularly those that are already mass loaded.

Auditorium 23 Speaker Cables
The Auditorium 23 cables are hand-made rather than "off the roll" like most other cables and designed specifically to be the interface between vacuum tube electronics and high-sensitivity loudspeakers. The Harbeth Super HL5s aren't exactly high-sensitivity but apparently Keith Aschenbrenner's Auditorium 23 speaker cables don't mind because they work beautifully together (and with everything else I've tried them with too). They have been my favorite cable since trying them. Each speaker cable consists of four conductors: two twisted conductors for each leg, one wire being smaller than the other, each twisted pair wrapped in soft green cotton sheathing. While Keith will not divulge the secret recipe of his cables, based on what I heard while listening I would hazard to guess that one conductor in each leg is copper, the other either silver or silver-plated copper. Each of the cables is terminated with thin and light beryllium-copper banana connectors designed to interfere as little as possible with the signal. They are about as close as you can reasonably get to the very best possible connector possible - none at all.

Shindo Laboratory Interconnects
Ken Shindo's Silver interconnects proved a synergistic match to the rest of the system. They are rather plain looking with non-exotic low-mass connectors and Ken Shindo is a bit secretive about his creations so about all I could find out about them are that they are silver with a "symmetrical
construction with Teflon dielectric." Whatever the story is with these interconnects, they sound great and have a lot of synergy with this system.