Simaudio Moon P-5 preamplifier & W-5 power amplifier Measurements, SimAudio Moon W-5

Sidebar 4: Measurements, SimAudio Moon W-5

A full set of measurements of the SimAudio Moon W-5 was made using its unbalanced inputs, with selected measurements repeated in the balanced mode, as noted below.

Following its 1/3-power, one-hour preconditioning test, the W-5's heatsinks were hot, though not to an unusual degree. The W-5 is noninverting from its unbalanced input; pin 2 of the balanced input is positive. DC offset measured a very low 0.9mV in both channels.

The W-5's input impedance measured 49.9k ohms (97.2k ohms balanced). The output impedance measured under 0.015 ohms at 20Hz and 1kHz, increasing to a maximum of 0.035 ohms at 20kHz. The amplifier's voltage gain into 8 ohms measured 30.6dB, unbalanced and balanced. The S/N ratio at 1W into 8 ohms measured 90.3dB over a 22Hz-22kHz bandwidth (unweighted), 83dB over a 10Hz- 500kHz bandwidth (unweighted), and 92.6dB A-weighted.

Fig.5 shows the W-5's frequency response. (Only the unbalanced result is shown; the balanced is virtually identical.) The 10kHz squarewave response (fig.6) is textbook, with good risetime, no overshoot or ringing, and a cleanly rounded leading edge. This is typical of all good amplifiers, and indicates a gradual high-frequency rolloff at ultrasonic frequencies. The 1kHz squarewave (not shown) was ideal. Fig.7 shows the W-5's crosstalk. While there is a measurable difference between the two channels, the overall levels are so low as to make this insignificant.

Fig.5 Moon W-5, frequency response into (from top to bottom): 1W into 8 ohms, 2W into 4 ohms, and 2.828V into simulated loudspeaker load (0.5dB/vertical div.).

Fig.6 Moon W-5, small-signal 10kHz squarewave into 8 ohms.

Fig.7 Moon W-5, Crosstalk (from top to bottom): L-R, R-L (10dB/vertical div.).