TESTED: Conrad-Johnson ET2 Preamp & LP66S Stereo Power Amplifier

Equipment report
Categories:
Tubed power amplifiers
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Products:
Conrad Johnson ET2
TESTED: Conrad-Johnson ET2 Preamp & LP66S Stereo Power Amplifier

Entry-level may mean different things to different manufacturers, but at C-J it definitely does not denote a major sonic penalty relative to its ultra-high-end products. Cost containment may be implemented through circuit simplification, judicious passive part substitutions, or watered-down cosmetics. Well, since C-J’s design philosophy already emphasizes simplicity—“circuits should be kept as simple as possible”—that mostly leaves the other two cost-cutting avenues open. The ET2 with its acrylic tube cage is surprisingly far more upscale-looking than one would expect from its price tag. The LP66S power amp, on the other hand, does project a Spartan appearance, especially with its tube cage off. But as you will soon discover, component quality—a major factor in any C-J product—is still extremely high.

A major part-selection decision was necessary in the case of the ET2’s volume control. According to C-J’s Lew Johnson, a discrete stepped attenuator would have ideally been the top choice in a pecking order in which a standard potentiometer defines the lowest step on the totem pole. He opted for the middle ground, a high-performance Burr-Brown volume-control-chip. One advantage this chip affords is the ability to remotely control volume without the need for an on-board motor. Another is the ability to adjust volume in 0.5dB steps, while most discrete stepped attenuators can only do 1dB steps. Because this is a stereo control, it is possible to adjust left and right channel volume independently to obtain balance control. The preamp’s sensible front-panel layout displays volume settings with sufficient size to be easily discernible (at least with my glasses on) from across the room. I found the modest-looking remote control to be perfectly adequate. Two external processor loops are provided, one of which is designed expressly for the addition of a surround-sound processor to a two-channel system. The other is conventional and allows the connection of a tape deck or equalizer.

Lew Johnson was kind enough to describe for me the basic circuit topology for both products under review, and what follows is based on this information. The ET2 linestage features a single gain stage. Following the volume control, the signal is applied to the grid of a Mullard M8080 medium-mu triode, which was billed by Mullard as a reliable RF power triode. The gain stage is direct-coupled to a high-current MOSFET buffer circuit to achieve low output impedance, and this arrangement comprises C-J’s Enhanced Triode (ET) circuit.

The optional phonostage’s input is a 12AX7 dual triode operated in parallel for reduced noise. It is coupled through a passive RIAA equalization network to a second gain stage which deploys a single section of either a 12AX7 (high-gain version) or a 12AU7 (low-gain version). As with the linestage, the signal is direct-coupled to a MOSFET buffer stage for low output impedance. The high-gain phonostage is best suited for low-to-medium-output moving-coil cartridges with a rated output of 1.0mV or less. The low-gain phonostage is recommended for cartridges with a nominal output above 1.0mV. No global loop feedback is used in this product. Due to the linestage’s single gain stage, the ET2 inverts signal polarity on all of its outputs.

Separate discrete regulated power supplies are used for the linestage and phonostage plate circuits. It’s worth emphasizing that resistor and capacitor choices are top-notch—no skimping here! A peek inside the chassis is worth a thousand words! Plate resistors for all stages are large Vishay metal-foil resistors, while all other resistors are precision metal-film types. Plate power supplies use polypropylene capacitors with Teflon bypasses (0.15uF) exclusively. Output coupling capacitors are a composite of polypropylene and Teflon, while the RIAA network capacitors are polystyrene types.

The LP66S is rated at 60Wpc into 4 ohms, and the output transformer is wired that way by default. There is only a single set of binding posts, so there’s no selection of impedance taps for a particular speaker load. However, the amp may also be ordered with 8- or 16-ohm load connections. This amplifier’s circuit is also about as simple as can be. The input voltage gain stage (half of a 6922) is direct-coupled to another 6922 which is configured as a coupled-cathode phase splitter and also provides the drive voltage for two pairs of Russian 6550 beam power tubes operated push-pull. The output stage is connected in ultralinear (UL) mode to the output transformer. Even over 50 years after its invention, UL remains a popular alternative to pure pentode mode, and that’s what the LP prefix in the model name refers to: Linear Pentode. A limited amount of loop feedback is used to obtain a reasonable damping factor and to minimize distortion levels. Plate supply voltages for both the input and phase-splitter circuits are regulated. You won’t find electrolytic caps anywhere in this amplifier. This is most unusual (and an added expense) for any amplifier, let alone an entry-level product. All caps are polypropylene and polystyrene types, including the main power-supply storage reservoir, which is polypropylene. All resistors are metal film. The output transformers are the same wide-bandwidth designs used in the more expensive LP70S amplifier. Bias adjustment is a piece of cake due to built-in LED bias indicators which allow the user to properly set the bias using only a supplied screwdriver.

Initial listening tests were conducted with both amp and preamp in the system. Later, they were auditioned separately to assess their individual performance attributes. It didn’t take me long to determine that the sonic character of the duo was being dominated by the power amp. Therefore, let me start with the ET2 preamp and give it its moment in the sun before returning to the power amp. Used as a linestage, the ET2 won me over pretty dang quickly, garnering excellent marks in several key areas. I’m not going to mince words when it comes to the bass range; pitch definition was remarkable, and bass lines in general were resolved with a precision rivaling that of any linestage I’ve auditioned to date, regardless of cost. The treble range, while fully under control, sounded a tad laid-back and short of air. There was never a hint of brightness or upper-register bite. Transients unfolded with plenty of speed and were allowed to decay delicately into a recording’s noise floor. The overall presentation was clean, smooth, and highly detailed, with an emphasis on harmonic accuracy. The ET2 was capable of revealing low-level nuances without sounding analytical. But it refused to add fat to the midrange, and harmonic textures were free of euphonic upper-midrange coloration. As a result, timbres were allowed to bloom without any sonic makeup. The truth and nothing but the musical truth is what the ET2 is all about. For me it was a joy of discovery, as the ET2 was able to zoom in on a particular voice or instrument and nail its timbre with authenticity. On the other hand, if you’re looking for a linestage to spice up or glorify your system, then the ET2 is probably not for you. It is not a romantic, lush, or assertive preamp. It’s not overtly tubey, but then it was not meant to be.

Please don’t misunderstand me. The ET-2 is an engaging linestage with plenty of kinetic energy and rhythmic drive. It has all the tools, the technique if you will, but it can also dish out the music’s passion and drama. It’s just that it does not sound like a vintage tube preamp. Going back as far as the 80s, I have yet to audition a C-J preamp that did not excel in imaging, and the ET2 was no exception. It erected a soundstage with a convincing depth perspective and fleshed out image outlines with almost palpable presence. The gift of imaging seems to be a family trait of the C-J preamp line.

My sample of the ET2 was outfitted with the optional low-gain phonostage—a good match for my Grado Reference moving-iron cartridge. My conclusion was that the phonostage, with only a couple of minor exceptions, complemented the ET2’s strong sonic suites. Its solid imaging, very good detail retrieval, bass definition, and low noise floor made for a pleasurable vinyl playback experience. The only negatives noted were a touch of textural grain, which may be a function of the Russian 12AX7s, and a slight dynamic reticence in scaling loud passages. Nothing serious, in hindsight, and the optional phonostage strikes me as a cost effective way to expand the functionality of the ET2.

In contrast with the ET2, which could best be described as intent on accuracy, the LP66S came across sonically as a swashbuckling romantic. Tonal emphasis was squarely on the lower midrange. It painted a much more convincing vintage tube impression. Harmonic textures were slightly liquid and warm, complimentary to violin tone, not excessively lush, but just enough to let you know that you’re listening to a tube amplifier. The treble range was laid-back, and in general, the overall presentation lost a bit of transient speed and tension. Despite dishing out 60Wpc from a pair of 6550s, there was no gratuitous upper-octave brightness and very little evidence of odd-order harmonic distortion products. The combination of these factors resulted in a mellow, relaxed presentation. Although the amp came across as somewhat broad-brush in character, there was still an abundance of low-level detail. The lack of multiple impedance taps made it impossible to experiment with optimizing bass damping. Bass definition was just OK with the Esoteric MG-20 loudspeaker, but improved to decent while driving the Basszilla Platinum Edition DIY speaker. These findings suggest the need for a careful audition in the context of your own system. When it comes to imaging, the LP66S evinced plenty of tube magic. Image outlines were solidly anchored within the soundstage. When partnering the ET2, it easily kept pace in this respect, giving full scope to a deep and spacious soundstage.

Entry-level? I don’t think so! Sonic compromise? Not so much. Despite its entry-level label, the ET-2 is a low-distortion, high-resolution device that delivers timbral accuracy on top of phenomenal bass control. It can certainly hold its own in elitist company. The optional phonostage can also be confidently recommended. If you’re in the mood for mellow tube sound with an exceptionally low listener-fatigue factor and plenty of imaging magic, be sure to give the LP66S an audition. It would make the perfect partner for a bright-sounding loudspeaker.

SPECS & PRICING
Conrad-Johnson ET2 linestage preamplifier
Gain: 28.5dB
Maximum output: 5.5Vrms
Distortion: Less than 0.1% THD
Frequency response: 2Hz to 100kHz, +0/-1dB
Phase: Phase-inverting
Weight: 15 lbs.
Dimensions: 13.75” x 19” x 3.315”
Price: $3800

Conrad-Johnson ET2 Optional Phonostage
Gain: 54 dB (high-gain option); 40 dB (low-gain option)
RIAA equalization: +/-.5dB, 20Hz to 20kHz
Phase: Phase-correct
Price: $1250

Conrad-Johnson LP66S Power Amplifier
Power output: 60Wpc, 30Hz–15kHz at no more than 1.5 % THD or IMD, both channels driven into 4 ohms (also available connected for 8 or 16 ohm loads)
Sensitivity: 0.5V to rated power
Frequency response (at 10 watts): 20Hz to 20kHz, +/-0.25dB
Hum and noise: 102dB below rated power
Input impedance: 100k Ohm
Tube complement: 3 x 6922, 4 x 6550
Weight: 45 lbs.
Dimensions: 16” x 19” x 6.38”
Price: $4300

CONRAD-JOHNSON DESIGN, INC.
2733 Merrilee Drive
Fairfax, VA 22031
(703) 698-8581
www.conradjohnson.com

ASSOCIATED EQUIPMENT
Final Sound 1000i electrostatics, Esoteric MG-20, Venture Audio Excellence III Signature, and Basszilla Platinum Edition Mk2 DIY speakers; Kuzma Stabi Reference turntable outfitted with Graham Engineering model 2.5 tonearm and Grado Reference cartridge; Air Tight ATE-2 phono preamplifier; PrimaLuna Eight CD player, Weiss Engineering Jason Transport and Medea DAC, Altmann Micro Machines Attraction DAC; Concert Fidelity CF-080 line preamplifier, Spread Spectrum Technologies Ambrosia preamplifier, First Watt B1 buffer preamplifier; Esoteric A-100 and Audio Space Ref. 3.1 (300B) amplifiers; Bybee Speaker Bullets; FMS Nexus-2, Acrotec 6N and 8N copper, Kimber Select KS-1030, Kimber KCAG interconnects; FMS Nexus speaker cable