Creek CAS4040 amplifier Lab Report

Lab Report

Back in the day this inaugural amplifier from an unknown 'upstart' brand attracted a mix of good and bad reviews. Was it really a '30-watter'? And what about that claim to deliver an 'instantaneous peak current' of 10A? Nearly 40 years on we have the tools to put any such concerns to rest... In practice, this refurbished CAS4040 did itself proud by offering a full 2x28W/8ohm and 2x35W/4ohm with – importantly – sufficient in reserve to accommodate peaks of 39W, 58W, 75W and 95W into 8, 4, 2 and 1ohm loads under dynamic conditions [see Graph 1]. The latter adds up to a maximum current delivery of 9.75A (10msec at <1% THD), all of which helps explain why the CAS4040 sounded (sounds) a lot bigger than it looks! Our sample also sounds somewhat beefier than perhaps it should thanks to a bass shelf amounting to +0.2dB/200Hz up to +0.95dB/20Hz. The HF is 'flatter' at –0.45dB/20kHz and –4.3dB/100kHz but then neither the bass nor treble tone controls can be truly defeated from the circuit.


Dynamic power output versus distortion (up to 1% THD) into 8ohm (black trace), 4ohm (red), 2ohm (cyan) and 1ohm (green) speaker loads


Distortion versus frequency at 1W/8ohm (black, 5Hz-40kHz) and 10W/8ohm (red, 20Hz-20kHz)

Channel balance is also a little wayward, but this is an original stereo volume pot after all. At 0dB attenuation (full volume or a gain of 33.5dB) the imbalance is just 0.2dB, but at mid-volume (20dB gain) it is closer to 1.5dB. Distortion was a little lower on the left than right channel here, but both were extremely consistent with power output, holding to around 0.05% (very close to the rated 0.045%) through midband frequencies. Indeed, while distortion increases at low (0.4%/20Hz) and high frequencies (0.16%/20kHz), this trend holds steady from 1W-25W [see Graph 2]. Noise was a couple of dB off specification, but the A-wtd S/N of 78dB (re. 0dBW) is acceptable for the era. PM

Power output (<1% THD, 8/4ohm): 28W / 35W
Dynamic power (<1% THD, 8/4/2/1ohm): 39W / 58W / 75W / 95W
Output imp. (20Hz–20kHz/100kHz): 0.015–0.045ohm / 0.123ohm
Freq. resp. (20Hz–20kHz/100kHz, 0dBW): +0.95dB to –0.45dB / –4.3dB
Input sensitivity (for 0dBW/25W): 16mV / 130mV
A-wtd S/N ratio (re. 0dBW/25W): 77.6dB / 91.6dB
Distortion (20Hz-20kHz, 10W/8ohm): 0.048–0.16%
Power consumption (Idle/rated output): 5W / 98W
Dimensions (WHD) / Weight: 420x60x185mm / 4.5kg