Preamplifiers
Pass Labs XP-10 Stereo Preamplifier
- Written by John E. Johnson, Jr.
- Published on 29 October 2012
On the Bench
Distortion measurements were made within an 80 kHz bandwidth. The XLR inputs and outputs were used for all tests, and the volume control was set to 75 (unity gain, i.e., input voltage delivers the same output voltage, or close to it). I adjusted the input voltage for each test to produce 2 volts RMS output (except where noted).
At 1 kHz, there was a scant 0.001% THD+N. The second order harmonic is predominant. This is exquisite performance. The spectrum is different than the XP-20 and XP-30, where the third order harmonic was a bit higher than the second order harmonic.
At 19 kHz and 20 kHz, there were only two side-bands (the peaks on either side of the 19 kHz and 20 kHz peaks), and the B-A peak at 1 kHz was 105 dB below the fundamentals.
IMD was extremely low, at 0.001%. This is what gave me that clarity with the full symphony orchestra. Low IMD means no mushiness in the midrange, which would otherwise throw a towel over the music.
THD+N vs. Frequency is shown below. At 2 volts output, the curve is nearly flat, and even at 5 volts output, the curve rises at 20 kHz only to a bit less than 0.01% THD+N.
Here, we see THD+N vs. Output Voltage (the volume control was set to 75 - Unity Gain). With a 100 kOhm load, the soft knee was at 4 volts, the hard knee at 13 volts, and clipping at 15 volts. With a 600 ohm load, the output drops. One would never encounter a 600 ohm load under normal circumstances. This is just a stress test.
The measured frequency response was 20 Hz - 20 kHz, - 0.5 dB.
Audio
