Power amplifiers stereo — VTL S-400 Series II Reference

The S-400 Series II Reference is a flagship stereo power amplifier from VTL, an American tube-amplifier specialist, built to deliver substantial output in either tetrode or triode operating mode from a single stereo chassis. Sitting within VTL's reference-tier catalogue, the S-400 Series II Reference brings the brand's flagship monoblock philosophy into a more space-efficient two-channel format.

Key specs that matter

Output power is 300W per channel in tetrode mode, dropping to 150W in triode mode - both substantial figures for a stereo tube amplifier, reflecting VTL's considerable output-transformer and power-supply engineering. Input sensitivity ranges 1,000-2,000mV, with input impedance held at 48k ohms on both balanced and single-ended connections. Frequency response spans 20Hz-20,000Hz within plus-or-minus 3dB, with an impressive 90dB signal-to-noise ratio for a tube amplifier at this power level. Maximum power consumption reaches 1,600W. At 290 x 610 x 610mm and a formidable 159kg, the S-400 Series II Reference demands serious equipment support consistent with its flagship-tier positioning.

Sound and use context

Expect the switchable tetrode/triode operation to reshape the amplifier's character - tetrode mode delivers maximum output and control for demanding loudspeakers and larger rooms, while triode mode trades some power for the more intimate, harmonically rich presentation triode operation is traditionally prized for.

Pairing

The substantial 300W-per-channel tetrode output and 48k ohm input impedance suit demanding, lower-sensitivity loudspeakers directly, and the wide input sensitivity range accommodates preamplifiers with varying output levels.

Alternatives

VTL's monoblock Siegfried Series II Reference sits above this stereo S-400 at even greater output and price, worth considering instead if a specific system and loudspeaker pairing calls for more power than this stereo chassis provides. VTL's decades of tube amplifier manufacturing experience, evident across both its monoblock and stereo amplifier ranges, ensure the same core engineering philosophy carries through consistently regardless of chassis configuration. Recommended overall for buyers wanting flagship VTL performance in a single stereo chassis. A fine stereo tube amplifier choice overall. Recommended. Highly recommended.