Mark Levinson No.326S Preamplifier and No.432 Power Amplifier

Equipment report
Solid-state preamplifiers
Mark Levinson No. 326S
Mark Levinson No.326S Preamplifier and No.432 Power Amplifier

The $10,000 No.326S is a single-chassis preamp based on the highly acclaimed No.32 Reference preamplifier, a $15,950 two-box unit introduced in 1999. The No.32 was, astonishingly, the first preamplifier to which the then-27-year-old company applied the designation “Reference.” Unlike other audio companies that use the term for marketing purposes, Mark Levinson reserved that special word for products that embodied the company’s best possible effort. Levinson Reference gear served as an internal benchmark for what could be done in a product category, and as an ideal to which to aspire in subsequent, less-costly designs. Levinson had introduced Reference power amplifiers, digital processors, and transports, but never a preamplifier until the No.32.

The No.326S’s chassis is smaller than that of most components, but the styling cues (curved front panel, matte aluminum buttons, red LED display) are unmistakably Mark Levinson. Interesting features include the ability to customize the unit by naming each input, deactivating unused inputs, adjusting the gain-offset of each input, and assigning the record-out jacks to an input. A unity-gain bypass mode (called “SSP” for surround-sound processor) allows the No.326S to be used with a home-theater controller. The controller’s left and right outputs feed one of the 326S’s line inputs. With the 326S in SSP mode, it’s as though the preamp isn’t in the signal path. This connection method, which I use in my system, allows you to have a two-channel signal path completely separate and uncorrupted by a surround-sound system. In a nice touch, switching inputs or absolute polarity causes the volume to quickly ramp down before switching, and then ramp up to the previous level, preventing pops or other noises from reaching your loudspeakers. Optional phono boards ($1400) convert the No.326S from a linestage to a full-function preamplifier.

The 326S’s fundamental design is dual-mono, with the left and right audio channels physically separated in the chassis and powered from completely separate supplies. Only the AC power cord is shared between channels. The internal topology is fully balanced, which requires that an unbalanced input signal be converted to balanced by a phase splitter at the input. A differential amplifier at the output converts balanced signals back to unbalanced. This topology adds additional circuitry to the signal path for unbalanced signals. The upside is that balanced signals remain balanced from input to output. Note that a truly balanced preamplifier, such as the No.326S, employs four signal paths (+/– left, +/– right) and four volume-control elements rather than two.

The No.326S’s volume control is a work of art. Identical in design and execution to that developed for the No.32 Reference, it is a stepped attenuator using a discrete-resistor array. The front-panel volume knob’s motion is converted into digital data which then engages the resistor network to achieve the desired attenuation. Volume can be adjusted in 1dB increments up to 23dB, and 0.1dB increments above 23dB. Levinson introduced the switched-resistor volume control in the No.38 preamplifier, but that unit employed an MDAC (multiplying digital-to-analog-converter), an IC that provided digital control over analog signals. The No.326S’s volume control is significantly more sophisticated, employing discrete resistors rather than resistive elements in an IC. Advantages of a switched-resistor network over a traditional volume control are that the audio signal is never subjected to the wiper and resistive element in a potentiometer, and that high precision can be achieved between the left and right channel gain. Even more important in a fully balanced preamplifier, perfect gain matching is possible between the + and – phases of the balanced signal. From a user’s point of view, the switched-resistor network and front-panel volume display allow precise level setting and matching—a feature of even more utility to a reviewer.

The No.326S’s circuit boards are made from Arlon, a material developed for circuit boards used in microwave and radar applications. It reportedly has ideal properties for audio, including low dielectric loss and exceptionally low conduction between traces. Because Arlon is extremely expensive it is reserved for Mark Levinson’s more costly products.