Preamplifiers — Ubiqaudiolab Ubiquitous 300B

The Ubiquitous 300B is a hybrid valve preamplifier from Ubiqaudiolab of Ljubljana, the Slovenian audio brand of the Akrapovič Group, and the only control unit in a range otherwise made up of Ubicube mono power amplifiers. Ubiqaudiolab calls it a cost-no-object design and an analogue hub for its monoblocks. After years of trying different circuits, the company settled on a minimalist hybrid design centred on the Western Electric 300B, a triode that Western Electric introduced in 1938 and has recently put back into production. Ubiqaudiolab assembles every unit by hand.

Key specs that matter

All connections are balanced XLR - five inputs, two variable outputs and one fixed output. Input impedance is 200 kohm and output impedance is 0.01 ohm. Gain is +8 dB in balanced mode. The frequency response spans 1 Hz to 1 MHz at the -3 dB points, and phase shift at 20 kHz is below 0.1 degree. Channel separation, like the S/N ratio, is better than 110 dB. Total filter capacitance is 236,000 µF. The chassis measures 480 mm wide, 490 mm deep and 153 mm high, and the preamplifier weighs 29 kg.

Engineering and use context

The topology is dual mono in class A, with the two channels laid out as mirror images in separate compartments. Each channel has a fully symmetrical balanced J-FET input stage in class A, followed by one current-production Western Electric 300B in a single-ended class A intermediate gain stage. The maker quotes a tube life of 40,000 hours, and a built-in counter tracks the hours used. Volume is set by a solid brass ALPS RK501 Gold potentiometer turned by a stepper motor that Ubiqaudiolab designed itself. The custom remote has a rotary control with 330 steps of 0.3 dB and variable rotation speed, following a logarithmic volume law. Power comes from a pure unregulated switch-mode supply made of seven modules, feeding a Mundorf capacitor bank. Coupling and decoupling use Jupiter copper foil and Mundorf zinc foil capacitors, and the output is protected against DC. Critical circuitry is shielded against electromagnetic interference inside a solid aluminium chassis with optimised grounding, which stands on mechanically damped feet. A push button in the top plate switches between standby and on.

Pairing

Ubiqaudiolab engineered the Ubiquitous 300B to work with its own Ubicube monoblocks, whose single XLR inputs take its balanced outputs directly. Every source has to connect over XLR, since the preamplifier offers no single-ended sockets. Ubiqaudiolab develops its electronics with large loudspeakers from Wilson Audio, Magico and Marten, as well as Living Voice horns.

Alternatives

Ubiqaudiolab makes no other preamplifier, so the Ubiquitous 300B is the brand's only model in this category.