Integrated Amplifiers

Inspired by AVID's longstanding Pulsus phono preamp [HFN Nov '12] the Sigsum's part-passive/part-active RIAA network's gain options are specified as 48dB (MM), 60dB (MC Low) and 70dB (MC High). In practice they are rather higher at 59.4dB, 71.5dB and 83.0dB because the phono stage is also tied through the line preamp, adding another ~12dB. While this implies a very high sensitivity of 1.07mV (MM), 266µV and 71µV (MC Low and High) this maximum gain can, of course, be moderated via the volume control!

Nevertheless the input margins are borderline with the MM stage overloading at 44mV (+18.9dB headroom re. 5mV) and the MC Low/High at 11mV and 2.9mV, respectively – so avoid the highest output MMs. Otherwise, distortion is low at ~0.002% midband [red infill, inset Graph] and the response [black trace] is flat to ±0.5dB from 20Hz-20kHz with the same high treble lift (rising to +5.7dB/100kHz) we saw in the Pulsus. Noise is low, too, with A-wtd S/N ratios that work out at a generous 86.2dB (MM), 73.4dB (MC Low) and 74.7dB (MC High). PM