Integrated Amplifiers

PrimaLuna typically runs its power stages at a conservative anode/screen voltage (417V here), sacrificing a potentially higher power output for improved tube life – a sensible compromise for enthusiasts eager to minimise downtime and running expenses. The EL34-equipped version tested here is rated at 2x42W in UL mode and 24W in triode mode, although its literature suggests both 1% and 2% THD. In practice the clipping point is fairly sharply defined so there's little extra power at a 2% limit – 2x55W in UL and 2x28W in triode modes into 4/8ohm loads via the 4/8ohm taps, respectively. All test results for triode mode are in parentheses, below. Furthermore there's sufficient headroom to accommodate 69W (32W), 69W (33W), 80W (35W) and 64W (33W) into 8, 4, 2 and 1ohm loads via the 8, 4, 4 and 4ohm taps, respectively [see Graph 1, below].

Overall gain is only about 0.8dB lower in triode mode (+36.3dB vs. +37.1dB) – possibly sufficient to influence quick A/B listening comparisons – but the triode setting also benefits from a 3dB boost to an already generous A-wtd S/N ratio (88.8dB vs. 85.8dB, re. 0dBW). Negative feedback is typically reduced to increase the gain of triode mode at the expense of distortion, but the difference is not large here – 0.082-0.55% in UL to 0.13-0.48% in triode mode at 1W/8ohm (20Hz-20kHz), and 0.17-2.9% in UL to 0.45-5.6% in triode mode at 10W/8ohm [see Graph 2]. I discuss the impact of the EVO 300's moderate 2-3ohm output impedance (via 8 and 4ohm taps) on frequency response in my boxout, although both modes exhibit a +2.5dB 'bump' at a subsonic 5-6Hz, so you might care to plug the ports of big, reflex-loaded loudspeakers if you choose to spin some vinyl! PM