Classé Audio’s flagship preamplifier, the Six, has enjoyed a five-year life span—quite long for an audiophile component. Company president Glen Grue reports that the Six’s sales have continued to improve during that time. How to explain this solid-state preamp’s continued success in competition with today’s newer, remote-controlled, line-stage preamplifiers?

How about these factors: value, convenience, ergonomics, and sonics. High-end “value”—a difficult term to define—resides in a product’s sonics, reputation, and price; even in the “feel” of its controls. The Classé Six sits squarely in the top quartile of available preamplifiers. It is more expensive than all but 20% of the 413 preamps listed in Audio‘s 36th Annual Equipment Directory (October 1993, pp.122–137). Using this guide, the Six seems rather typical: It can be ordered with a built-in phono stage (like 46% of the 84 high-end preamps); it has an external power supply (found in 44% of these); and it does not use remote control (only 15% of over–$3300 preamplifiers in the 1993 listing are remote-controlled).

The Six’s internal phono stage will appeal to audiophiles who enjoy LPs and don’t want to pay $2000 extra for an excellent phono stage. Many preamps listed in Stereophile‘s “Recommended Components”—including the Jeff Rowland Consummate, the Audio Research LS2B, and the Sonic Frontiers SFL-1—must be used with an external à la carte phono stage, which must perforce be more expensive than an internal card (footnote 1).

Description
Since its introduction in 1989, the Model Six reviewed here has undergone subtle changes in its external appearance. It began as the DR-6, a reference to David Reich, the audio designer who founded Classé Audio and who was involved in the DR-6’s original design. David has since moved first to Archtech Electronics, then to Theta Digital; since his departure, Glen Grue and his staff have redesigned the preamp, dropped the “DR” designation, and spelled out the “Six.” The Six Mk.II has sculpted handles and no rack-mount cutouts on the front panel.

In a 1992 review (The Abso!ute Sound, Issue 79, p.91), Antony Cordesman described the Six as a “well styled ‘black box’…where form follows function, and no attempt is made to miniaturize the unit or give it a clever appearance.” The 19″-wide faceplate, available in either silver or black, has rounded edges and four large rotary switches whose knobs have a flattened section for easier handling. The front-panel controls, from left to right, include a source-selector rotary switch that allows the owner to select CD, Phono, Balanced, Tuner, or Aux. Next is a rotary switch with Rev, Left, Stereo, Right, and Mono positions. The right upper panel has a rotary Balance control with a single central detent, and a detented Volume control with an Off position. These rotary switches have the smoothest action I have found on any preamplifier. The four toggle switches across the bottom of the panel are, from left to right, a Tape switch for monitor or source, a Bypass Mode switch that selects phono or balanced, another Bypass On/Off switch that selects the bypass mode, and a Mute switch.

The bypass function is new with the Six Mk.II and replaces the DR-6’s polarity-reversal switch. This control is reminiscent of similar bypass switches in Walter Jung preamp designs as published in The Audio Amateur. Jung found that a reduced number of switch contacts improves the sound (footnote 2). The Six’s bypass removes the input selector, tape, and mode switches from the signal path. To operate the bypass function, first move the input-selector switch to the desired input. Though the signal does not travel through this switch, the latter chooses which input does not get shorted to ground. Possible bypass inputs include the Phono or CD inputs on the phono model—Balanced In or CD on the Six L. Thus, to listen to a Phono selection, select Phono with the upper-panel rotary switch, and throw the Bypass Mode toggle to Phono; then switch the Bypass On/Off function switch On.

The back panel features standard XLR-balanced connectors (male connectors for Main Out and female connectors for Balanced Input), and gold-plated RCA input jacks for CD, Tuner, Aux, and Tape. The power cable connecting the preamp and the large power supply is very thick; as is the unit’s power cord, which has a large, yellow, hospital-grade plug. The Six’s Phono input is replaced by Aux 2 on the Six L. A toggle switch is located between the left- and right-channel phono inputs on the Six. This switch is pushed up for MC operation, down for MM. In the MC position, 20dB of additional gain is added to the MM’s 35dB. The MC gain can be adjusted between 20 and 40dB by replacing resistors R15 and R16 on the preamplifier’s system board. The stock resistors need to be unsoldered and replaced with the others (supplied, along with silver solder). There are no provisions for adjusting input impedance for the MC inputs. The Six used in this review was set for the appropriate gain for my Spectral phono cartridge.

Technical description
With the exception of the MC and MM phono circuits, all Classé amplifiers and preamplifiers use the same circuit, tailored to different power levels. Classé maintains that the differences between the top-of-the-line and economy models reside in parts quality, power-supply design, and the amount of filtering. The Six’s circuitry first appeared in the Model 9 in 1987, and was refined in 1988. Only by listening to the same circuit over and over during this six-year period did Glen Grue and his staff discover the best ways to obtain the smoothest, most detailed sound. Their listening sessions were conducted at the factory and in the designers’ homes.

The Six uses 1% custom metal-film resistors, polystyrene and polypropylene capacitors, special printed circuit boards, and switches and controls that feature silver and gold contacts. The Six’s separate power supply has a large, high-current toroidal transformer, eight stages of regulation, 104,600µF of filter capacitance, and extra capacitor filtering of both the beta (current gain) main output stage as well as a local supply to the input differential amplifier.

The Six Mk.II substitutes new, small-signal transistors in this differential circuit. Grue reported that using many small-signal transistors creates a circuit with smoother sonic characteristics than using two higher-voltage transistors. Also, the Mk.II employs newly developed ultrasonic bypassing techniques. Bypassing occurs not just in the power supply but in the system board as well, with special attention to emitter resistors and output devices. The balanced input circuitry and the balanced high-level section feature completely discrete individual circuit components for the hot and cold signals and the left and right channels. A cascode amplifier is coupled to a current gain stage.

Before a Six is assembled, its output transistors are mounted on a large grid and burned in for months. By the time they’re matched for assembly, enough drift has been eliminated that the Six’s sound should change minimally over time. Low-level devices are also matched carefully at build time.


Footnote 1: The Six’s $3295 price falls in the middle of Stereophile‘s Class B recommended preamplifiers.

Footnote 2: See Greenhill, L., “Test Report. A Subjective Listening Test of the PAT-5/WJ-1A,” The Audio Amateur, Vol.11 No.1, January 1980. In this test, an inexpensive, single-switch, Jung-modified Dynaco PAT-5 did as well as a Mark Levinson ML-1 preamplifier in a double-blind listening-panel test involving eight men and women.