Solid State Power Amp Reviews

A full set of measurements of the YBA Passion 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 Passion's heatsinks were hot, though not too hot to touch, and well within the normal range of temperatures usually encountered during pretest.

The Passion's input impedance measured 49.4k ohms (106.9k ohms balanced). The output impedance measured under 0.15 ohms at 20Hz and 1kHz, increasing to a maximum of 0.17 ohms at 20kHz. Voltage gain measured 31.5dB (25.4dB balanced) into 8 ohms. Signal/Noise referenced to 1W into 8 ohms measured 90.7dB over a 22Hz-22kHz bandwidth unweighted, 82.3dB over a 10Hz-500kHz bandwidth unweighted, and 93.3dB A-weighted. (S/N measurements were taken with both the balanced and unbalanced inputs shorted.)

The Passion is noninverting when driven from its positive, unbalanced input; at the balanced, XLR input terminal, pin 2 is positive. DC offset measured a very low 2.6mV.

Fig.1 shows the frequency response of the Passion. (The unbalanced result is shown; the balanced is a virtual overlay of this.) There is little worthy of comment here. The same is true of the 10kHz squarewave response (fig.2), which is near-textbook, with good risetime, and no overshoot or ringing. (The 1kHz squarewave, not shown, shows the merest hint of overshoot on its leading edge but no ringing, and is otherwise just about perfect.)

Fig.1 YBA Passion 1000, frequency response at (from top to bottom at 6kHz): 1W into 8 ohms, 2W into 4 ohms, and 2.828V into simulated loudspeaker load (0.5dB/vertical div.).

Fig.2 YBA Passion 1000, small-signal 10kHz squarewave into 8 ohms.

The THD+noise percentage vs frequency curves are plotted in fig.3. Note that the distortion into lower impedances is somewhat higher than is typical, but is still respectable. The higher levels may be the result of the low-feedback design. The waveform of the distortion at 4W into 2 ohms is shown in fig.4. It is heavily second-harmonic, with some noise. The distortion waveforms (not shown) into 4 and 8 ohms were identical.

Fig.3 YBA Passion 1000, THD+noise vs frequency at (from top to bottom at 1kHz): 4W into 2 ohms (unbalanced, balanced), 2W into 4 ohms (unbalanced, balanced), 1W into 8 ohms (unbalanced, balanced), and 2.83V into simulated loudspeaker load.

Fig.4 YBA Passion 1000, 1kHz waveform at 4W into 2 ohms (top), distortion and noise waveform with fundamental notched out (bottom, not to scale).

The Passion's output spectrum driving a 50Hz sinewave at 255W into 4 ohms is shown in fig.5. While the distortion products are higher here than we typically see—the maximum value is -56dB, or about 0.17%, at 100Hz—this is a very good result, considering the very high power level at which it was taken. The same can be said for the high-frequency intermodulation spectrum shown in fig.6, at 255W into 4 ohms (the 1kHz difference component lay at -56dB; again, about 0.17%). The results for an 8 ohm load at 156W are shown in fig.7. The trend is similar to the 4 ohm spectrum, though the numbers are slightly different. The IM distortion at 1kHz drops to -72dB (0.025%) into the 8 ohm load.

Fig.5 YBA Passion 1000, spectrum of 50Hz sinewave, DC-1kHz, at 255W into 4 ohms (linear frequency scale).

Fig.6 YBA Passion 1000, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 255W into 4 ohms (linear frequency scale).

Fig.7 YBA Passion 1000, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 156W into 8 ohms (linear frequency scale).

The 1kHz, THD+noise vs output power curves for the Passion are shown in fig.8. Again, the distortion prior to clipping is somewhat higher than we normally see, though not unreasonable. The discrete clipping levels for the Passion are shown in Table 1.

Fig.8 YBA Passion 1000, distortion (%) vs continuous output power into (from bottom to top): 8 ohms, 4 ohms, 2 ohms.

Table 1 Discrete Clipping Levels (1% THD+noise at 1kHz)

The YBA Passion is a powerhouse that produced a solid set of measurements to go along with the excellent sound quality reported by JS.—Thomas J. Norton