Pre/Power Amplifiers

With no integrated DAC or phono stage on board – CH Precision offers the partnering C1.2 and P1 to service digital and vinyl sources, respectively – the L1 remains a fully analogue, balanced line preamplifier. The volume control ‘number’ reflects absolute gain, so ‘0.0dB’ is just that: a 1V input realises a 1V output. Relay clicks are audible when advancing the volume rotary above 0.0dB, above +6.0dB and above +12.0dB, indicating additional R-2R gain blocks being switched into service, but the accuracy of all steps, above and below 0.0dB, is spectacularly precise. From 0.0dB to the maximum +18.0dB volume setting (a gain of 1:7.95), the ±0.5dB steps are accurate to within +0.02dB. Similarly, from 0.0dB down to –90.0dB (a total of 180x0.5dB steps) the maximum error is just –0.01dB, slackening off slightly to ±0.03dB over the final 9dB to –99.0dB. This represents a tolerance of ±0.03dB and a channel balance accuracy of ±0.01dB over a full 117.5dB dynamic range. Remarkable...

The L1’s maximum balanced output is a very healthy 22.1V from a flat 26ohm source impedance (20Hz-100kHz) while the input overload threshold is >14V. The frequency response is unaffected by volume position, being flat to within ±0.01dB from 1Hz to 20kHz and ‘rising’ to +0.07dB/100kHz [see Graph 1].

Noise is exceptionally low (–101.3dBV or 8.6µV, unwtd, 20Hz-20kHz) and the A-wtd S/N correspondingly very wide at 103.2dB (re. 0dBV) while distortion easily bests the <0.001%/1kHz spec. with a very low 0.00014-0.00035% (20Hz-20kHz, re. 0dBV). There is necessarily some minute change in THD with gain and output level, but the minimum distortion achievable typically occurs over a 3-6V output at 0.00009-0.00015% [re. 20Hz-20kHz; see black trace, Graph 2 below]. PM