Pre/Power Amplifiers

Combining a triode line stage with a FET output need not mean ‘triode/pentode amp’ levels of distortion, but PrimaLuna has jumped hoops to ensure the ‘colour’ of the EVO 300 Hybrid ‘poweramplifier’ is as close to that of the all-tube EVO 300 [HFN Mar ’21] as possible. We saw much the same in its earlier EVO 300 Hybrid integrated amp [HFN Jan ’22], these still being the only hybrid amps in the range. Both amplifiers employ a three-stage tube front-end – the first 12AU7 triode forms a phase-inverting gain stage, followed by another 12AU7 triode to restore absolute phase. The final triode is a unity gain cathode-follower that drives the two pairs of MOSFETs, per channel, in the power amp. All three tube sections have separate, FET-regulated PSUs and all the transformers are made on site at PrimaLuna’s factory. That includes input, output and PSU transformers.

Of course, the ‘integrated’ EVO 300 Hybrid has higher overall gain than the ‘poweramp’ [see PM's Lab Report] but there are no active circuit changes here. Instead, the tube stage(s) provide the same 7dB of gain but the audio signal is subsequently attenuated by 7dB in the ‘poweramp’ prior to the FET power amp. While the triple triodes provide no overall gain, they do impart a ‘tube sound’, says Jan de Groot, Prima’s engineer from Floyd (the codename for everything ‘FET’ within PrimaLuna’s amplifiers). ‘I saw a similar technique being used in the mid-’80s when I was a service engineer for Luxman’, Jan recalls. ‘We also prefer to use a balanced-to-SE (XLR) input coupling transformer’, says Jan, ‘An active input stage may have lower distortion but the sound of our custom transformer was preferred.’ More tube/FET hybrid amps will be released soon, no doubt... PM