Pre/Power Amplifiers

The Unico DM v2 is both colourful and powerful and, courtesy of its remarkably low 0.002ohm source impedance and sub-1Hz bass extension, will grip your loudspeaker in an infrasonic vice. Unison Research rates this v2 a little higher than the original DM model at 220W/8ohm and 340W/4ohm, figures that are fairly comfortably exceeded at 2x240W and 2x405W, respectively. Overall gain is just +20.45dB (XLR in) so a full 4V output will be required from your (Unico Pre v2) preamplifier to raise the rated 220W. The S/N ratio is still above average at 88.4dB (A-wtd, re. 0dBW) and the residual noise a ‘soft white’ in character. Back to the subject of power where Unison also suggests a ‘670W/2ohm peak’ and, indeed, there’s sufficient headroom in that PSU to support 270W, 505W and 782W into 8, 4 and 2ohm loads, respectively, under dynamic conditions [see Graph 1, below]. The 782W/2ohm is cut short by electronic protection as is the 175W/1ohm [green dashed trace], though the maximum current still works out at a generous 19.8A (re. 1kHz/10msec at <1% THD). The amplifier’s response, meanwhile, is flat and extended all the way up to –0.1dB/20kHz and –1.4dB/100kHz.

The aforementioned colour is discussed in our boxout for while the tubes set the harmonic pattern, the overall level still increases with output power from 0.025%/1W to 0.074%/10W, and 0.22%/100W to 0.33% at the rated 220W (all re. 1kHz/8ohm). Versus frequency [see Graph 2, below], distortion is fairly ‘flat’ up to ~1kHz but rises thereafter from 0.008-0.04% at 100mW/8ohm [grey trace], 0.03-0.65%/1W [black trace] and 0.06-0.5%/10W [pink trace, all re. 20Hz-20kHz/8ohm]. Finally, stereo separation is a fabulous >100dB (20Hz-20kHz). PM