Pre/Power Amplifiers

In common with the Ultima Preamp [HFN Feb '19] the Ultima Pre 2 offers six levels of overall gain: 'x0.5', 'x1.0'... 'x2.5 and 'x3.0' amounting to –0.3dB, +5.3dB, +9.9dB, +12.1dB, +14.0dB and +15.4dB, balanced in/out, respectively. Maximum output level is 10V regardless of gain (so the input overload is a marginal 1.7V in the x3.0 gain setting), from a 96ohm source impedance, while the 'useable' range of its 99-step volume control is ~53dB. Optimum channel balance, in our sample at least, was achieved at the 1 o'clock position (12 o'clock yielding a L/R channel error of 0.65dB). Intriguingly, the A-wtd S/N ratio is significantly improved over the Ultima Preamp's 83dB (re. 0dBV) at 96.6dB while distortion is lower, and lowest in the x3.0 gain setting where 0.0002-0.0023% compares against 0.0003-0.0085% in the x0.5 mode [black vs. blue trace, Graph 2]. Regardless of gain, the Pre 2's response is flat to within ±0.1dB from 1Hz-100kHz.

The partnering Ultima 2 monoblock did not quite make its continuous 750W/1305W 8/4ohm power rating – 690W/1285W was nearer the mark at <1% THD – but the three ±110V PSUs operating in parallel delivered a magnificent 810W, 1590W, 2963W and 4850W into 8, 4, 2 and 1ohm loads under dynamic conditions [see Graph 1, below]. At 1kHz/8ohm, THD increases very gently with output from 0.002%/1W, 0.003%/10W and 0.0035%/100W up to just 0.0045%/600W. THD increases by a factor of ~20x at 20kHz, reaching 0.008%/10W [red trace, Graph 2]. Output impedance increases from a low 0.018-0.020ohm (20Hz-1kHz) to 0.09ohm/20kHz and 0.91ohm/100kHz, and the response rolls gently away at HF to –0.23dB/20kHz and –2.95dB/100kHz (10W/8ohm). PM