[SoundStage!]Factory Tour
Feature Article
March 2004

Convergent Audio Technology
by Doug Blackburn

In a corner of a modern technology park in a suburb of Rochester, NY you’ll find the entrance to Convergent Audio Technology, better known as CAT to high-end cognoscenti. CAT emerged in 1985 as a manufacturer of tube preamps that garnered widespread praise from reviewers and owners. Periodic upgrades and enhancements have kept the SL1 preamp in the top echelon. The current model is the SL1 Ultimate Mk. II, selling for $5950 as a line stage only and $6950 with phono stage. After success with the SL1 preamp, CAT tackled amplifiers, immediately going up-market with the $30,000-per-pair JL1 Signature monoblocks, then the $50,000-per-pair JL1 Limited monoblocks. More recently, CAT introduced the JL2 stereo amp at $11,995 and then discontinued its JL1 mono amps due to the JL2's superior sound quality at a much lower price. Subsequently, CAT introduced the JL3 Signature monoblocks at $29,995 per pair to replace the JL1 Limited monos at the top of the line.

Top CAT Ken Stevens designs and refines his company's products. During my tour, Ken spoke with great animation about the battles specialty audio manufacturers have to fight. Large companies (i.e., Vishay, a resistor manufacturer) buy smaller companies and one day your supply of non-Vishay resistors starts to dry up. What do you do? Roll over and settle for something that doesn’t sound as good, or battle with a multinational company that really isn’t interested in your order for several thousand pieces?

Stevens does battle, holding true to his goal of finding the most neutral components possible and using only those components in CAT products. Unlike high-end companies that aim at delivering a specific sound, CAT's goal is utter neutrality -- no sound, no character, no imprint. "Just let the music through," as Stevens says. Stevens illustrated his point with a story about a capacitor manufacturer who said, "Just tell me what you want. I can make a capacitor that will sound any way you want it to sound." What Stevens wanted was a capacitor that "sounds like water" -- a concept that baffled the manufacturer beyond his capacity to respond.

This incident was a reaffirmation of Stevens’ decision a number of years back to purchase a capacitor-winding machine from an about-to-retire capacitor manufacturer -- the only person who could make capacitors that filled Stevens’ "sounds like water" requirement. Of course, the capacitor-winding machine would have been of little value without the expertise of the retiring manufacturer using it. Fortunately, the deal for the machine included training in all the finer points of "rolling your own" capacitors from raw materials. Stevens' ability to experiment with the winding machine led to a specific set of winding parameters, materials, and assembly techniques that give him the "sounds like water" neutrality he has pursued for so many years.

It would be a pleasure to discuss some of these parameters with SoundStage! readers, but Stevens understandably requested that his intellectual property be protected. He prefers not to give other manufacturers a tutorial on using materials and techniques that they might find useful in making better-sounding capacitors. I can tell you that Stevens no longer uses Teflon dielectric for the "film" part of the film-and-foil capacitors he manufactures. He has a replacement material with some parameters that would seem to be trouble at first glance, but in actual use the material is "remarkable" according to Stevens.

You may wonder, as I did, what the big deal is about this capacitor-winding machine. It really is not an impressive object -- it's made mostly of Plexiglas so old it is turning yellow. But it does everything it needs to do very effectively, giving Stevens a remarkable degree of control over every conceivable winding parameter. Stevens commented that some high-end manufacturers refuse to believe he is manufacturing his own capacitors. Perhaps the photo and my eyewitness account will convince them.

CAT's capacitor-winding machine. This photo has been digitally altered to obscure some proprietary features of the device.

CAT JL2 output transformer sub-assembly in temporary protective box.

An SL1 Ultimate Mk II preamp and power supply.

SL1 Ultimate Mk. II preamps awaiting installation of phono-stage components. All of the white components visible in the photo are proprietary CAT capacitors.

Exposed JL2 amplifier power supply components are isolated from the rest of the amplifier’s components inside a metal cover. The power transformer is on the left.

JL2 amplifier electrical assembly showing a combination of proprietary white CAT circuit boards and point-to-point wiring.

One recurring theme throughout the CAT tour was how uniformly bad-sounding and colored Stevens finds "audiophile" electronic parts. If you are a tweaker you know all the brand names of all the famous and probably not-so-famous parts in audiophile favor as replacements for inferior stock parts in many audio components. Stevens keeps up with the latest parts to be certain he isn’t missing anything useful. But he believes that if he had to use tweaky parts instead of the parts he has carefully selected, his preamps and amps would not sound nearly as good. Stevens feels strongly that audiophiles are attracted to parts that sound the most different rather than parts that sound the most neutral, the most "like water."

One of several racks used to hold in-progress units during the assembly process. CAT products are not built from the ground-up in one continuous build. Sub-assemblies get produced in batches first.

This rack holds individual components and has space for a few sub-assemblies. The small boxes on the top shelf contain single values of various resistors and capacitors.

The CAT factory listening room. The big rig is at Ken Stevens' house.

CAT amps and preamps don’t follow a single design or assembly philosophy. Stevens finds that point-to-point wiring doesn’t sound as good as his Teflon circuit boards (proprietary, of course), but he does use point-to-point wiring when it makes sense and sounds better than what he can produce with a circuit board. When asked about a large pile of parallel resistors soldered to a circuit board rather than a single larger resistor, Stevens’ matter-of-fact reply is that it simply sounds more neutral than any other solution. In that location, the current is much too great for the good-sounding low-current resistors Stevens favors. Unable to find larger, higher-current resistors that sound as good, Stevens simply parallels the appropriate number of his best-sounding low-current resistors to get the current handling the circuit requires.

Another recurring theme is mechanical resonance control. Stevens finds that sometimes he needs to eliminate resonance with damping materials. Other times he needs to isolate resonance. Cut-to-size bright-blue damping panels line much of the interior of the CAT preamp and companion power-supply chassis. Proprietary isolation feet mount the transformer to the chassis to prevent resonance of the vibrating transformer from reaching the chassis.

Amplifier output transformers are completely epoxy potted with embedded birch-plywood panels. Why birch plywood? Because of all the materials experimented with, it produced the least-colored sonic results and sounded even better than using only epoxy. The epoxy potting went through many iterations of "fillers" being added in an effort to improve the sound. Stevens found that the yellowish, nearly transparent epoxy with no additives sounded better than any of the concoctions that were tested, so that’s what is used. Stevens is well aware that chassis materials have their own contribution to the sound, so he has made careful selections after a lengthy process of listening to different chassis materials to be certain his choices would produce the ultimate "like water" sound.

What you get in finished CAT products is more than just a preamp or amp. You get a bit of Ken Stevens’ attention to detail -- perhaps obsession is a better way to put it -- as well. You get his accumulation of public and private libraries of transformer-design documentation. You get his years of working towards and finally being able to manufacture his own capacitors. You get decades of experience with tubes themselves, so he’s always aware of precisely the best tubes to install in his products.

In fact, don’t get him started on the subject of tubes unless you have a lot of time to listen to what goes on behind the curtains. He’s rather annoyed and disgusted by the tube sellers who cater to the high-end market. Big names you would recognize have sold CAT owners well-used vintage tubes that were supposed to have been new old stock (NOS). Stevens found tube sellers sticking these customers with high-priced "perfect" NOS tubes that were actually factory rejects that failed quality tests. Stevens has seen his customers get hooked into all sorts of tube boondoggles, including supposed "perfect" and very expensive vintage tubes that were nothing more than brand-new tubes from Russia or China. The original factory markings were removed and carefully copied vintage markings were applied. Next time you are ready to buy expensive vintage tubes from the Ben Dover Tube Company, you may want to think about what might actually be in the boxes.

CAT maintains a small factory listening room that houses Merlin VSM-Millennium loudspeakers, Argent Room Lens room-tuning devices, a modified Audio Note DAC-3 DAC, a CAL DX-1 transport, a CAT SL1 Ultimate Mk II preamp, and the day of my visit a JL2 amp. Stevens’ personal listening room where the most serious evaluations are performed hosts some of the finest high-end equipment money can buy. Stevens wants to keep his finger on the pulse of the high-end market and know how CAT products perform with a cross-section of the most elite high-end loudspeakers and source components.

CAT is an inspiring high-end company dedicated to building the best possible products via obsessive attention to detail. Stevens has little use for high-end flim-flammery designed to seduce consumers. Instead, he goes for nothing more "magical" than ultimate neutrality achieved through real engineering, experimentation, and listening. What else is there?

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