It's no longer in production, but the Proton D-540 is still a quality home stereo component. In 1987 the D540 won "Audio/Video International" magazine's Hi-Fi Grand Prix award. The goal of an amplifier is to faithfully reproduce the input signal with as much power and as little distortion as possible, and the Proton D540 does just that.
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The Proton D540 is driven by dual power supplies with Proton's patented dynamic power on demand technology, which increases headroom. In a 20 ms test, the amplifier delivers 160 watts per channel to an 8 ohm load, 280 watts per channel to a 4 ohm load and 380 watts per channel to a 2 ohm load. In a 100 ms test, the amplifier drives 150 watts per channel to an 8 ohm load, 220 watts per channel to a 4 ohm load and 230 watts to a 2 ohm load, and it has 6 dB of headroom. The D-540 has outputs for two sets of stereo speakers.
Frequency Response and Distortion
The frequency response curve is from 20 - 20 kHz, +/- 0.2 dB. The low modifier means that the amplifier's response curve is flat and consistent, so it accurately reproduces the recording. At the rated power level, the total harmonic distortion is 0.02 per cent, and the intermodulation distortion is 0.06 per cent. Both distortion levels are so low as to be practically negligible. It's significant that the distortion is measured at the rated power level, because that means that the distortion level is consistent up to the maximum rated power. The damping factor is 90. The damping factor is the ability of the amplifier to stop the woofer when it's not playing. Higher is better, and it's a good comparison point with other amplifiers.
Inputs and Controls
The amplifier has a phono input, radio tuner, video, digital audio and two tape inputs with multidirectional dubbing. The phono preamp has a switchable setting for low-output MC phonograph cartridges or high-output MM cartridges, as well as three-way adjustable capacitance for setting the response of the preamp. The amplifier is bridgeable, meaning that both channels can be used to drive a common mono load. The amp features dials for bass, treble, balance and volume and selector switches for loudness, bass EQ, and mono/stereo. The bass and treble controls have a +/- 9 dB range.
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