Power amplifiers mono — Octave Audio Jubilee 300 B

Octave Audio of Germany builds the Jubilee 300 B as a mono class A single-ended valve amplifier within the company's Jubilee line. Each chassis runs three 300 B directly heated triodes in indirect parallel operation, so stereo playback calls for a pair. Octave builds it around its exclusive zero feedback technology, and the owner can choose an output of 15 to 30 W depending on the selected amplification mode.

Key specs that matter

Two inputs are fitted, one RCA and one balanced XLR, and the speaker terminals offer separate 4 ohm and 8 ohm taps. Octave lists a frequency range of 20 Hz to 50 kHz at -3 dB measured at full power. Two gain settings are provided. In the high position gain is 30 dB, input sensitivity is 0.5 V and noise sits more than 100 dB down, while the low position gives 19.5 dB of gain, 1.7 V sensitivity and more than 110 dB of signal to noise ratio. Each unit stands 660 mm tall on a 240 mm wide, 400 mm deep footprint and weighs 55.0 kg. The US price for two units is USD 80,000.

Engineering and use context

Filament heating is handled by a linear 7 Hz generator developed by Octave, which feeds each of the three triodes with its own separately regulated sine wave voltage. Octave explains that ordinary 50 Hz AC heating produces too much hum, while DC heating limits what the 300 B can do, and the 7 Hz supply removes line frequency ripple and RF interference while allowing the valves to run in parallel. Heating and operating voltages are also controlled electronically. A power preselection function sets the quiescent current in three stages - low, medium and high, equal to 25 mA, 50 mA and 70 mA per 300 B - which lets the amplifier accept different makes of 300 B valve. Bias for the output triodes is shown on a dedicated display. The protection system combines soft start electronics that delay inrush current with a circuit guarding the output valves, while an eco mode lowers consumption when the amplifier is idle. The housing is offered in silver or black aluminium, and the middle section can be ordered in birch, walnut or Makassar veneer.

Pairing

Its XLR and RCA sockets take either type of line output from a preamplifier, and the two gain positions allow the input sensitivity to be matched to the preamplifier level. An optional bi-amping package adds level adjustment, switchable gain and a low-cut filter below 100 Hz, and a remote switching option is also offered.

Alternatives

Within the same Jubilee line, the Octave Jubilee Mono Ultimate is a monoblock using eight KT 170 valves and rated at 440 W into 4 ohms.