Measurements
Usual caveat: Measurements are merely slices of reality. They can never encompass the full reality of listening experience. Yet when properly interpreted, they do reveal underlying physical mechanisms that correlate, to a limited degree, with listening experience. With the recognition of their limitations and capabilities, they can be a useful guide in evaluating the performance of audio equipment.
FFT Spectrum @1W into 8 ohms
The FFT (Fast Fourier Transform) spectrum @ 1W into 8 ohms, with both channels driven simultaneously. The distortion is dominated by the HD2, HD3, and HD5, which are around -110dB (0.0003%) or below. Notice the low levels of the 60Hz and its harmonics (120, 180, etc), indicating high immunity to power supply noise and ground loops.
FFT Spectrum @1W into 4 ohms
The FFT spectrum @ 1W into 4 ohms, with both channels driven simultaneously. The behavior is similar to the 8 ohm case, except for the slight rise in the second harmonic.
FFT Spectrum @50W into 8 ohms
The FFT spectrum @ 50W into 8 ohms, with both channels driven simultaneously. The distortion is dominated by the HD2, which is around -109dB (0.0004%). Note the exceptionally low level of 60Hz and its harmonics (120, 180, etc).
THD+N vs. Output Power
THD+N (Total Harmonic Distortion + Noise) vs. output power with 1KHz signal into 8 ohms. At lower power levels, the THD+N is limited by the noise floor. As the power level increases, the THD+N decreases and eventually dips below 0.0007%. (The slight step around 14W is due to the gain switching in the measurement system.)
IMD
IMD (Intermodulation Distortion), 19K+20KHz @ 50W into 8 ohms. This is just about the worst-case test that pushes the limits of the amplifier's ability to track high-frequency signals. The 2nd order IMD product at 1 KHz is exceptionally low, at -116dB. The 3rd order IMD products around 19K/20KHz are below -114dB.
Pulse Response
10KHz pulse @ 1.5Vp-p into 8 ohms. The response is well behaved and settles quickly to the final value, with a characteristic single-pole response. (The noise on the flat part of the pulse is due to that of the digitizing oscilloscope.)
Gain & Frequency Response
Frequency Response @ 1W into 8 ohms. The response is flat to within 0/-0.15dB from 20 to 20KHz. The -3dB points extends from 4Hz to 140KHz. The intrinsic bandwidth of the amplifier is much higher, around 800KHz, but is intentionally limited at the input for improved immunity to electromagnetic interference.
Crosstalk (Channel Separation)
Crosstalk @ 50W into 8 ohms. The crosstalk is about -120 dB at 1KHz and -95dB at 20KHz in both directions, from left to right channel, and from right to left channel. Such a low level of crosstalk approaches that which can be attained with monoblock amplifiers.
Notes:
- All measurements are performed with the Audio Precision APx525 system, except for the pulse response. Unless otherwise indicated, FFTs are 64K points, averaged 4 times, with the AP-equiripple window.
- Each unit is shipped with a printout of measurements. See an example of the measurement summary.