– Audio Precision APx555 B-Series Analyzer
– Amplifier was warmed up for 6 hours before measuring.
– AudioQuest Mackenzie XLR interconnects
– Neurochrome Headphone Dummy Load
– Full reports containing additional data and test configurations are attached
– Exact analyzer/filter configurations for each measurement are detailed in the full reports
– All measurements shown below are taken with a 32 ohm load via balanced output unless otherwise specified
– 4v tests were done in Medium Gain, 700mv and 50mv tests were done in low-gain as these provided the best results.
Reports available here (These contain 4v, 700mv and 50mv test results, please check you’re looking at the right ones when comparing!):
Gain: 23.4dB (High), 5.6dB (Med), -3.8dB (Low)
Output impedance: 0.2 Ohm (Goes lower at higher frequencies though)
Power quite happily meets and even exceeds the spec by a bit.
1khz 4v input 300 ohm (Med Gain Pot Maxed):
1khz 4v input, 700mv out, 300 Ohm (Headphone level):
1khz 4v input, 700mv out, 32 Ohm (Headphone level):
1khz 4v input, 50mv out, 12 Ohm (IEM level Low Gain):
THD+N performance is excellent across the board. There’s probably not going to be any situation where you’d need to go out of medium gain, but regardless the performance is good in all three settings.
93dB THD+N at 50mv is excellent, making this one of the lowest noise amps available for running IEMs.
THD+N / Frequency:
Small amount of rising noise/distortion into the higher frequencies.
SINAD/THD+N vs output level:
IMD (SMPTE) vs Output Level:
Crosstalk is where things look a little strange. As this level of crosstalk does not seem to be proportional to the signal level. So when we look at the crosstalk at 50mv IEM levels for example we see it’s quite high:
I’m not sure why this is, but it could explain why when using the amp with IEMs and more sensitive headphones the staging and imaging felt a bit strange.
This seems to be the only area where this amp has any real ‘problems’, but it is unusual especially given as the THD+N @ 50mv is about 93dB.
1khz Square Wave: