Very Budget Amplifier from Crown
Good performance, lots of features including DSP based EQ, crossover, delay, etc. Construction quality is acceptable, although flimsy. Not bad for such a budget amplifier. Single PCB construction with virtually no wiring whatsoever makes for very inexpensive (and error-free) production.
Amplifier was tested in "DSP Bypass" mode, but the audio signal still goes through A/D and D/A conversion. There is no hard bypass of the digital circuitry (which operates at 48kHz sampling rate). As such, there was considerable phase shift at higher frequencies, and a 10kHz square wave was turned completely sinusoidal by the digital conversion stage filtering out all the harmonics. This may impact the transient response of the amplifier. This is not a form of distortion per se, but an act of signal filtration. Threshold of clipping showed no nasties whatsoever, and the amp clips gracefully at all frequencies and load impedances.
2R testing posed tough for the amplifier, current limiting its output after a second or so. It lasted longer at 1kHz as opposed to 40Hz or 10kHz.
Distortion was low even at full power, and hovered at about 0.08% at 3/4 power, but repeated sine testing at 4R (lid on) caused the amp to go into thermal limit. This is partly due to the push-on heatsinking arrangement where the output devices are bolted to a slab of aluminium, but the heatsink fins are push-fitted over the top. One of the eight heatsink blocks became very loose with a firm wiggle and may pose long-term reliability issues if used on the road. Thermal conductivity was sub-optimal through the push-fit joint as confirmed by the thermal images. (Allowances must be made for the differing IR emmissivity of polished metals, such as the heatsink fins, where temperature readings made by the thermal imaging camera can be 30 degrees or so lower than indicated. However, the emmissivity of the output devices and heatsinks in this case are virtually identical, so there is indeed a thermal gradient between them - see last image below).
|All results taken with sine wave input into a resistive dummy load of 8, 4 and 2 ohms (where applicable), two channels simultaneously driven (unless otherwise stated), at the threshold of clipping. These results should be considered maximum 'continuous RMS' power ratings (>5 seconds). Distortion measurements, labelled THD%, are taken with an HP8903A audio analyser (80kHz Bandwidth).|
|Power to weight Ratio1||130.7 W/kg|
|Notes||06-07-2010. Mains did not fall below 239V|
1 Power to weight ratio is calculated by taking the average of the power measurements at 4 ohms, multiplying by the number of driven amp channels, and then dividing this value by the weight of the amplifier.
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