Integrated Amplifiers

‘We reduced the distortion and increased the power’, says Unison Research in its broad-brush description of the Triode 25’s [HFN Jul ’15] evolution to this Black Edition And, in all respects, Unison’s claims are borne out on test, with the full 29W output in triode mode improving from 5% to 1% THD and distortion reduced from 1.0% to 0.085% at 10W (all re. 1kHz/8ohm). The A-wtd S/N is improved by 2dB and the output impedance reduced from 1.9-2.2ohm to a very linear 1.0ohm (20Hz-20kHz), improving both bass clout and the Black Edition’s resilience to different loudspeaker loads. Both old and new Triode 25s have the same +2dB sub-bass boost from 10Hz down to 1Hz but the top-end responses have changed – while the original had a very flat response out to 65kHz/–1dB, the newcomer has a gentle treble roll-off, falling to –1.5dB/20kHz and –15dB/100kHz.

I discuss the triode vs. pentode operation in our [see boxout] so the following relates to its pentode/high feedback mode. Power output broadly meets the 50W/6ohm spec. at 2x48W/ 8ohm and 2x38W/4ohm while there’s enough under the hood to support 56W, 54W, 43W and 32W into 8, 4, 2 and 1ohm loads, respectively, under dynamic conditions [and 33W, 35W, 30W and 25W in triode mode; dashed traces, Graph 1]. Distortion increases gently with level, from 0.03%/1W to 0.095%/4-12W and then up to 0.6W/45W (all re. 1kHz/8ohm) although these figures increase significantly with decreasing load impedance [again, see Graph 1]. Versus frequency, distortion necessarily increases at low frequencies with transformer core saturation (0.8%/10W/ 20Hz) and at higher frequencies with reduced compensation (feedback) at 3.7%/10W/20kHz [see Graph 2]. PM