Designed in Holland and made in China, PrimaLuna's amps are essentially classic valve designs, but they bring distinctive aesthetics and a few modern design touches to the party.

One such notable feature in the PrimaLuna Prologue Two amp we are reviewing here is 'Adaptive auto bias'. Bias is a long-standing pain in the neck of valve amps: quite simply it's the DC ('standing') current in the valves under conditions of no audio signal and it's critical.

Usually amps either have manually adjusted bias, which may even require test equipment to set, or auto-bias (also called 'self-bias'), which does what it says but, in the traditional implementation, reduces maximum output power. It's really surprising how few firms have done what PrimaLuna does and made solid-state monitoring circuits which control bias. It makes the amp far more tolerant of imbalance between output valves.

Input switching and volume control use good-quality mechanical components and behind them a good deal of the amp's circuitry is based on solid wiring and tag strips, with large resistors in most positions.

Critical capacitors are brand-name plastic-film parts, while a couple of substantial electrolytic capacitors are joined by a smoothing choke in the power supply. The valve complement, apart from the output KT88s, runs to two each of the ECC83 and ECC82.

PrimaLuna prologue two rear

The cover over the transformers is so very resonant that we'd be tempted to remove it!

Sound quality

Definitely a qualified success, this amp made a very favourable impression on one of our listeners and a mostly favourable one on a second, but failed to inspire the third.

It turns out that the unimpressed listener missed detail and insight more than anything and found it a struggle to hear details even in familiar recordings. On the other hand, the best-pleased listener referred to 'sublime vocals' and clearly enormously enjoyed the overall musicality of the amp's presentation, which certainly has great charm across the midband.

Opinions were united on the subject of imaging, which is good laterally but tends to bring the performers a bit further forward than one is accustomed to hearing.

Treble wasn't explicitly mentioned by our 'blind' listeners, but our sighted experience suggests it is well-extended without sibilance or spit. That's probably a contribution to the amp's good handling of vocals and it scores highly for the ease with which lyrics can be understood.

There was also specific praise for the PrimaLuna's handling of dynamics, which are full but surprisingly subtle – you often don't notice the music is growing in volume until it's really loud.

With an unusual balance of strengths, this amplifier certainly merits an audition.

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