EarMen Staccato/Tradutto/CH-Amp and PSU-3 Streamer/Headphone Amp Lab Report

Lab Report

Although the CH-Amp's core circuit design – based around TI's SoundPlus OPA1642 op-amps – is shared between the line/preamp output and headphone output, the latter does have its own output buffer that drops the (line) 96ohm source impedance down to a sub-0.8ohm level. This, in turn, ensures there's a mere 0.14dB drop into a 32ohm headphone load and minimal variation in amp/headphone frequency response. In fact the CH-Amp's native response is exceptionally flat (to within ±0.04dB from 10Hz-100kHz) while the A-wtd S/N is a wide 100.5dB (re. 0dBV) via the single-ended line or headphone output. Distortion is barely influenced by loading, the minimum of 0.00016-0.002% via the line outs (20Hz-20kHz, re. 0dBV) barely increasing to 0.00021-0.0016% at 10mW/32ohm via the unbalanced headphone output [red trace, Graph 2 below].

Two gain settings are offered via the front panel for the headphone outputs, equivalent to +2.8dB (Low) and +10.8dB (High), while the line/preamp has a maximum gain of +5.7dB. With an input headroom of 5.7V, these gain settings have no impact on the CH-Amp's maximum output of 7.15V (unloaded SE headphone out) so you can use the 'Low' setting with high sensitivity/high impedance earbuds without penalty. The low –98dBV residual noise is also a boon for high sensitivity cans. Under load, the headphone buffer will sustain 85mW/600ohm and 1280mW/32ohm (1.3W) with current to support 1.9W (1880mW) into very low 8ohm loads – all limited by protection [Graph 1]. Again, there's almost no increase in distortion when driving lower loads, starting at 0.00022%/10mW/600ohm to 0.00021%/10mW/32ohm and 0.0007%/10mW/8ohm [black, orange, red traces, respectively, Graph 1]. PM


Power output vs. THD into 600ohm (black), 32ohm (orange) and low 8ohm (red) headphone loads


Distortion versus frequency (preamp, black; headphone 0.6V unloaded, green; 10mW/32ohm, red)

Maximum output (<1% THD) 7.15V (pre)/ 7.15V (headphone)
Power output (<1% THD, 600/32/8ohm) 85mW / 1280mW / 1880mW
Output Impedance (20Hz-20kHz) 550-690mohm (96ohm, pre)
A-wtd S/N ratio (re. 0dBV/32ohm) 100.2dB / 100.5dB
Distortion (20Hz-20kHz, 0dBV) 0.00016–0.0020% (preamp)
Distortion (20Hz-20kHz, 10mW/32ohm) 0.00021–0.0016% (headphone)
Freq. resp. (20Hz-20kHz/100kHz) –0.01 to +0.01dB/+0.04dB
Power consumption 5W (1W standby)
Dimensions (WHD) / Weight (total) 150x30(60)x150mm / 2.1kg
Price £2999 (full system)

Chicago, IL, USA
Supplied by: SCV Electronics Ltd, Herts
03301 222500