Rogue Audio is one of those high-end paradoxes; it makes products that deliver fantastic performance in a fine overall package, yet don’t come with a price tag that looks like someone had to use up a lot of spare zeros. The new Sphinx integrated amplifier is a perfect example of this; it’s a well-made, very fine sounding hybrid line-and-phono design, with good power delivery and a solid case. It’s not even gone down the cheaper route of US design and ‘offshore’ build – it’s designed and built in the US, imported, shipped and delivered to your door for a shade under £1,500. That’s good value, when set against the ever-escalating prices endemic to audio.
All of which invites the question – why isn’t it better known?I suspect the answer lies in the word ‘hybrid’. Not the performance a hybrid design brings, but just the word ‘hybrid’ and the perception that brings to the table. In the case of the Sphinx, the word hybrid means it has a pair of JJ 12AU7 tubes in the preamplifier stage and a pair of Hypex UCD-180 Class D modules in the power amplifier to deliver its 100 watts per channel.
A Class D amplifier is a high-speed switching device. It uses a pulse width modulator as a comparator, referencing the input signal from the preamp stage against a generated triangular wave. The resultant binary waveform is then fed into a MOSFET-based amplifier that switches on and off accordingly (at very great speed). By then applying a low-pass filter after the amplifier stage, the high-speed switching component of the signal is filtered out and what’s left is an amplified version of the preamp’s signal. The main advantage to this is smaller circuit size (no heatsinks, no banks of output transistors) and higher efficiency (as in less heat, meaning greater reliability). It is frequently mis-labelled as a ‘digital’ amplifier (presumably because of the PWM comparator, and the letter ‘D’), but in the real world, it’s just a super fast analogue design. At least, that’s the theory; Class D has a less than stellar reputation among audiophiles, but those who dig deeper recognise that Class D can actually sound good, and the consistently good sounding Class D modules are generally from Hypex. We’ve seen these modules put to good use by Rogue before, in the Hydra and Medusa power amps (we tested the Medusa in issue 88).