Instruction Manual for HPA4 with 1.0.X Firmware – REV B Page 49
Graph 18 - FFT 10 kHz Tone at 22 dBu - Headphone Amplifier - 6 W into 16-Ohms
This plot shows that the THX-888 headphone amplifier stays extremely clean, even when
delivering 6 Watts at 10 kHz! The output level is 22 dBu (9.8 Vrms). The load impedance is 16
Ohms. Under these extreme high slew rate conditions, the 2nd and 3rd harmonics measure better
than about -124 dB (0.00006%) into a difficult 16-Ohm load! This test demonstrates the
effectiveness of the THX AAA™ technology which includes 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 10 kHz fundamental has been removed using a notch filter. This filter increases the
resolution of the AP2722 test system.
FFT_10kHz_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 *-131.738 dBr *-123.982 dBr
2 2
Red Solid 4
Fft.Ch.1 Ampl Left R HP Out into 16 Ohms : 8.00000 =Swr.Ch. A Input
-125.997 dBr B -123.818 dBr B
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