ICs for Audio Common Use
s
Technical Information (continued)
•
Structure of pre-amp. stage (continued)
AN5270
G
F
amp., the flat-amp., amplifies the signal equally for all frequencies in the range of 20 Hz to 70 kHz.
G
T
amp., the treble or tone-amp., has an internal LPF connected to its inverting input. The non-inverting input of G
T
amp. is connected to the input signal. Thus, the output of G
T
passes only the upper range of frequencies (cut-off
frequency
=
2.5 kHz).
G
B
amp., the bass-amp., amplifies the lower range of frequencies. Its cut-off frequency is determined by R1· C1.
If LF pin is left open, then G
B
amp. has no effect on the overall frequency response.
•
Gain calculation
General formula for gain of pre-amp. is (when vol.
=
max., tone
=
max.) :
G
pre
=
G
L1
· (G
F
+
G
T
)
−
G
B
· G
L2
By vector analysis as shown in fig. Vector diagram of G
pre
,
G
V
[dB]
=
G
pre
+
G
P
G
V
[dB]
=
20 log
√[G
L1
· (G
F
+
G
T
)
−
G
B
· G
L2
· cosθ]
2
+
(G
B
· G
L2
· sinθ)
2
+
G
P
where G
L1
=
0.5
G
F
=
1.3
G
B
=
5.4
G
T
0 for (100 Hz)
=
1.3 for (1 kHz)
2.5 for (10 kHz)
G
pre
G
P
=
25 dB
Z3 · 0.848
G
B
≈
Z3
+
R1
6600
Z3
=
√1 +
(2πf · C1 · 6600)
2
θ = −tan
−1
(2πf · C1 · 6600)
θ
G
L1
· (G
F
+
G
T
)
G
B
· G
L2
Fig. Vector diagram of G
pre
G
V
G1
−3
dB
G2
G3
*1
−3
dB
G1 : Gain at 100 Hz
G2 : Gain at 1 kHz
G3 : Gain at 10 kHz
f
1
: High frequency cut-off when Pin3 is open.
f
2
: Low frequency cut-off
Tone
=
max.
Tone
=
min.
100 Hz f
2
1 kHz f
1
10 kHz
f
Fig. Frequency response of AN5270
Note) *1 : This is the response if LF pin is open (i.e. R1 open).
5
PANASONIC [ PANASONIC SEMICONDUCTOR ]
