Benchmark HPA4 - Page 44

Instruction Manual for HPA4 with 1.0.X Firmware – REV B Page 44
Graph 13 - AC Line-Related Hum - Headphone Output
This FFT plot shows that AC line-related hum is at least 152 dB below the THX-888 headphone
amplifier's maximum output level of +22 dBu (use the right-hand dBr B scale)!
Notes:
• The scale on the left (dBr A) is dB relative to +28 dBu. This is the maximum input and
output level supported by the HPA4 line stage.
• The scale on the right (dBr B) is dB relative to +22 dBu. This is the input 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.
• Balanced inputs to headphone outputs, volume control set at 0 dB.
Audio Precision
07/13/18 16:47:12
FFT_Idle_Unity_Gain_Bal_HPA_Low_Freq.at27
Color
Sweep
Trace Line Style Thick
Data Axis Comment
Source 2 Cursor1
Cursor2
1 2 Green Solid
4 Fft.Ch.1 Ampl Left Left HP Output : 7.00000 =Swr.Ch. A Input
*-157.763 dBr *-159.010 dBr
1 3
Green
Solid 4
Fft.Ch.1 Ampl Right
: 7.00000 =Swr.Ch. A Input -151.763 dBr B -153.010 dBr B
2
2 Red
Solid 4
Fft.Ch.1 Ampl Left Right HP Output
: 8.00000 =Swr.Ch. A Input -170.357 dBr A -171.347 dBr A
2 3
Red Solid 4
Fft.Ch.1 Ampl Right : 8.00000 =Swr.Ch. A Input
-164.357 dBr B -165.347 dBr B
-170
+0
-160
-150
-140
-130
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
d
B
r
B
-180
+0
-170
-160
-150
-140
-130
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
-157.763
-159.01
d
B
r
A
20 400
40
60
80 100
120 140
160 180
200
220 240
260 280
300 320 340 360 380
180.196 300.02
Hz
dx=119.824 Hz
dy=-1.247 dB
7.00000