On the Bench (JEJ)

All the bench tests were with two channels driven.

At 50 watts into 8 ohms, IMD was 0.043%.

Measured frequency response was the same at 5 volts and 20 volts into either 8 ohms or 4 ohms: 10 Hz - 50 kHz, - 1 dB.

THD+N vs. Frequency for both 8 ohms and 4 ohms is shown below. The relatively high distortion at 20 volts and 4 ohms (100 watts) across the entire frequency range suggests that you should not use 4 ohm speakers with this receiver. At $399, the manufacturer simply cannot put a big enough power supply inside to handle low impedance loads.

At 8 ohms, the AVR-689 delivered 85 watts RMS into 8 ohms (two channels) before a rapid rise to clipping (1% THD+N) at 110 volts. At 4 ohms, the output was 110 watts, then a rise to clipping at 140 watts. Notice that at 4 ohms, distortion begins to rise rapidly at 20 watts, whereas at 8 ohms, it begins the rapid rise at 85 watts. This is another indication that you should not use the AVR-689 receiver to drive 4 ohm speakers.