Усилители мощности моно — MasterSound Monoblock 845

The MastersounD 845 Monoblock is a mono valve power amplifier whose output stage runs two 845 directly heated triodes in parallel single-ended configuration, pure triode and Class A, without negative feedback. MastersounD, founded in 1994, hand-builds it at its Arcugnano workshop near Vicenza and supplies the monoblocks as a pair.

Key specs that matter

Each chassis delivers 50 W in Class A from two 845 output triodes, driven by two 6SN7 double triodes. Rated bandwidth spans 2 Hz to 90 kHz within 0 dB, and full output needs 1 V of input signal. Inputs are one unbalanced RCA plus one balanced XLR, and loudspeaker loads from 4 to 8 ohms are supported. Bias is automatic and adjustable. Each unit draws 197 W from the mains, measures 44 x 39 x 24 cm and weighs 30 kg.

Engineering and use context

The wide bandwidth without feedback depends on the output transformer, which MastersounD designs specifically for this triode and winds by hand in its own workshop on a mechanical winding machine. The winding method was started by company founder Cesare Sanavio and developed further by his son Luciano, now head of production. Two 845 triodes working in parallel are what raise the output while keeping the stage single-ended, where a single 845 in the Compact 845 integrated gives 24 W per channel. The rear panel carries the bias adjustment input, a fused mains inlet and separate 4 and 8 ohm speaker terminals. The factory measures the valves before fitting them and burns each amplifier in for at least 48 hours before shipping. A red LED flashes at power-up and stays lit once the internal voltages are stable, and a thirty-minute warm-up is advised before critical use. The 845 runs at high anode voltage and gets very hot, so each chassis needs a solid, level support with free air above it, and valves should never be changed while the amplifier is on. The five-year warranty covers the amplifier but not its valves. Because every monoblock takes its own mains feed, two outlets are needed for a stereo pair.

Pairing

The 845 Monoblock needs a preamplifier with enough output to drive it fully, such as the MastersounD Phl 5 or Spettro valve preamplifiers, which both offer XLR and RCA outputs. With its moderate power from a feedback-free triode stage it suits speakers of 88 dB or higher sensitivity in rooms of 20 m2 and more.

Alternatives

The MastersounD PF 100 litz is a larger mono amplifier with four 845 triodes, Litz-wound output transformers and 107 W in Class A.