Integrated Amplifiers

The marriage of tubes and transistors, typically with a high voltage triode preamp stage preceding a solid-state power amp stage, is a popular 'blending' of technologies in hi-fi's high-end. Last month we saw the compact MA252 from McIntosh, but we've also tested some flagship behemoths that take the idea to its limit – Bascom H King's PS Audio BHK Signature 300 [HFN Jul '16] is one and T+A's anniversary M 40 HV [HFN Dec '18] another. Combining tubes with, specifically, MOSFET power devices is also not uncommon as we saw in the BHK amp and (in the driver stages) within the flexible T+A solution.

The same is claimed for the Unico Due where the ECC83 triode preamp is partnered with FET drivers and two pairs of bipolar power transistors (2SA1943/2SC5200) per channel. A form of signal-dependent 'Dynamic Class A' biasing is also claimed, but it's the triodes that dominate the technical fingerprint of this amplifier. In this example, and in other hybrid designs, a tube preamp stage might well be used to engineer some 'warmth' or other coloration into the overall sound [see Lab Report, p67], but this is not a given as the low distortion of Musical Fidelity's nuvistor/bipolar hybrid Nu-Vista 800 integrated [HFN Nov '14], among others, has ably demonstrated. PM