Benchmark HPA4 - Page 47

Instruction Manual for HPA4 with 1.0.X Firmware – REV B Page 47
Graph 16 - FFT 1 kHz Tone at 22 dBu - Headphone Amplifier - 6 W into 16-Ohms
This plot shows that the THD produced by the THX-888 headphone amplifier is extremely low,
even when delivering a very high 22 dBu output into a low-impedance 16-Ohms load. The output
power is 6 Watts per channel. The 2nd harmonic measures better than -127.5 dB (0.00004%)
under full rated load! The 3rd harmonic measures better than -126.5 dB (0.000005%)! This test
demonstrates the effectiveness of the THX AAA™ with feed-forward error correction.
Notes:
• The scale on the left (dBr B) is dB relative to +22 dBu. This is the signal level required to
drive an external AHB2 power amplifier to full output power. It is also the level required to
drive the internal THX-888 to full output power. It is also the level of the test tone.
• Balanced inputs to headphone outputs, volume control set at 0 dB.
• The 1 kHz fundamental has been removed using a notch filter. This filter increases the
resolution of the AP2722 test system.
Audio Precision
07/13/18 10:40:31
FFT_1kHz_Bal_HPA_16_Ohms.at27
ColorSweep Trace Line Style
Thick Data Axis Comment Source 2
Cursor1 Cursor2
1
2 Green
Solid 4
Fft.Ch.1 Ampl Left L HP Out into 16 Ohms
: 7.00000 =Swr.Ch. A Input -130.396 dBr B -126.744 dBr B
2 2
Red Solid 4
Fft.Ch.1 Ampl Left R HP Out into 16 Ohms : 8.00000 =Swr.Ch. A Input
*-127.591 dBr *-134.156 dBr
-190
+0
-180
-170
-160
-150
-140
-130
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
-127.591
-134.156
d
B
r
B
2k
32k
4k
6k
8k
10k
12k
14k
16k
18k
20k
22k
24k
26k
28k
30k
2.01329k3.01493k
Hz
dx=1.00164 kHz
dy=-6.565 dB