Denon 5805 Receiver Measurements Cont
At 175wpc our FFT distortion analysis again revealed stellar results. (+31.495+63.407)dBv = 94.902dBv (almost 10dB better than the Integra Research RDA-7.1) or 100*alog(-94.902/20) = .002%
At 303wpc into 4 ohms, the AVR-5805 did commendably well, though you could see the onset of higher order harmonics kick in. The (30.84+50.27dBv)dBv = 81.1dBv (about 1.1dB better than the Integra Research RDA-7.1 ) or 100*log^-1(-81.1/20) = .009%
The output impedance of the AVR-5805 is commendably low for an amplifier with a single pair of very powerful and well designed power transistors per channel. By weight of comparison, it's about 2x that of the Integra Research RDA-7.1 that featured 8 complementary output devices per channel and subsequently measured two feet deep. I consider this the ultimate compromise in performance, space, and budgetary constraints. The reason we emphasis so much importance on minimizing amplifier output impedance is because the lower the impedance, the less chance of system frequency response variation when driving reactive loads such as speakers and/or many exotic cables.
An amplifier that exhibits low output impedance will also exhibit excellent damping factor. The AVR-5805 maintained an impressive damping factor of over 50 throughout the entire audio bandwidth. These type of measurements are uncharacteristic of tube amplifiers or budget receivers which is where they usually fall apart when attempting to drive low impedance, inefficient speaker loads. This design is a far departure from that design characteristic.
At full power we see the AVR-5805 maintains its composure into an 8 ohm load with a meager increase in output resistance of 10mohms and almost identical damping factor. An excellent achievement!
The true test is how well an amp will hold up into low impedance loads. Ideally and amplifier should act like an ideal voltage source meaning power will double as load impedance halves since output voltage will remain constant. In order to do this, the amplifier output impedance must maintain a low enough level to not be the limiting factor.
As you can see, the output impedance is very similar to the 8 ohm full power test! Based on the principle of voltage divider, we should see about ½ the damping factor from our 8 ohm case.
No surprises there! This amp delivered the goods.
