BA3308 / BA3308F
Audio ICs
1/8
Dual preamplifier with ALC
BA3308 / BA3308F
The BA3308 and BA3308F are dual preamplifier ICs with built-in ALC circuits, and have been designed for use in stereo
radio-cassette recorders and tape recorders. They come in compact 9-pin SIP (BA3308) and 14-pin MF (BA3308F)
packages, and have two record / playback preamplifiers, and an ALC circuit. The preamplifiers have high gain and low
distortion, and can be directly coupled to the tape head without coupling capacitors. This prevents tape head
magnetization and “pop” noise generation.
A built-in rectifier means that an ALC circuit with good channel balance and large dynamic range can be constructed with
addition of just an external time constant circuit.
The ICs also include power-on mute circuits that suppress “pop” noise generation.
!
!!
!Applications
Stereo radio cassette recorders, cassette decks and home stereo systems and music centers
!
!!
!Features
1) Built-in ALC rectifier diode.
2) Wide operating power supply voltage range (VCC=6.0V to 14V)
3) Low current dissipation (IQ=3.5mV)
4) High gain (GVO=80dB)
5) Low distortion (THD=0.1%)
6) Low noise (VNIN=1µVrms)
7) Input coupling capacitors and not necessary.
8) Good ALC channel balance.
9) Power-on mute circuit.
10) ALC dynamic range can be varied by the addition of an external input resistor.
!
!!
!Absolute maximum ratings (Ta=25°C)
Parameter Symbol Limits Unit
V
CC
16 V
BA3308 Pd 950
∗1
∗2
mW
BA3308F 450
Topr −25 to +75 °C
Tstg −55 to +125 °C
Power supply voltage
Power dissipation
Operating temperature
Storage temperature
∗1 Reduced by 9.5mW for each increase in Ta of 1°C over 25°C.
∗2 Reduced by 4.5mW for each increase in Ta of 1°C over 25°C
(when mounted on a 70mm × 70mm × 1.6mm glass epoxy board).
!
!!
!Recommended operating conditions (Ta=25°C)
Power supply voltage
Parameter Symbol Min. Typ. Max. Unit
V
CC
6.0 −14 V
BA3308 / BA3308F
Audio ICs
2/8
!
!!
!Block diagram
123456789
ALC
MUTE
ch1
+
−
ch2
−
+
NF1
INPUT1
OUTPUT1
GND
ALC
V
CC
OUTPUT2
INPUT2
NF2
ALC
V
cc
1
2
3
4
5
6
7
14
13
12
11
10
9
8
+
+
−
−
N.C.
N.C.
N.C.
N.C.
N.C.
BA3308
BA3308F
!
!!
!Electrical characteristics (unless otherwise noted, Ta=25°C, VCC=7.0V, f=1kHz and BPF: 20Hz∼20kHz)
Parameter Symbol Min. Typ. Max. Unit Conditions
I
Q
1.5 3.5 4.5 mA V
IN
=0Vrms
G
VO
70 80 −dB V
OUT
=−10dBV
THD −0.1 0.3 % NAB34dB, V
OUT
=40mVrms
R
IN
15 25 45 kΩ−
V
OM
0.6 1.2 −Vrms THD=1%
V
NIN
−1.0 2.0 µVrms
ALC 40 45 −dB
∆ALC −0 2.5 dB V
IN
=−60dBV, −30dBV
CS 60 75 −dB V
O
=0dBV, NAB34dB
Quiescent current
Open loop voltage gain
Total harmonic distortion
Input resistance
Maximum output voltage
Input conversion noise voltage
ALC range
ALC channel balance
Channel separation
Conversion with R
g
=2.2kΩ and
NAB34dB at 1kHz
R
G
=3.9kΩ, V
IN
=−70dBV
reference, THD=3%
BA3308 / BA3308F
Audio ICs
3/8
!
!!
!Measurement circuit
Fig. 1
123456789
ch2
BA3308
ch1
ALC
MUTE
V
SW1A
321
2.2kΩ
SW6A
SW4A
3.9kΩ
10kΩ
30kΩ
120kΩ
1.2kΩ
33kΩ
39Ω
100µF
10µF
OUTPUT1
INPUT1
0.1µF
SW3A SW3B
0.1µF
INPUT1
OUTPUT2
10µF
100µF
39Ω
33kΩ
1.2kΩ
120kΩ
30kΩ
10kΩ3.9kΩ
SW4B
SW6B
2.2kΩ
1
2
3
SW1B
SW2B
1
2
1
2
330µF
22µF220Ω
1MΩ
SW5
V
CC
SW2A
V2V2V1
V
~
V1
V
~
V
~
V
~
V
~
!
!!
!Application example !
!!
!Application example circuit PCB (copper side)
Fig. 2
123456789
ALC
MUTE ch2
ch1
BA3308
4.3kΩ
120kΩ
39Ω
18kΩ18kΩ220Ω
3.9kΩ39Ω
3.9kΩ
1MΩ
0.027µF
100µF10µF
10µF
22µF
330µF
10µF
10
µ
F
100µF
7V
OUTPUT2 INPUT2
INPUT1 OUTPUT1
R
5
R
3
C
3
R
1
C
5
C
5
R
7
C
7
C
8
C
6
R
6
C
2
C
4
R
4
R
8
V
CC
R
2
R
9
(R
10
)
R
11
(R
12
)
C
9
(R
10
)
For playback, instead of R
5
and R
6
, connect
the following NAB time constant circuit
between pins 1 and 3 and 7 and 9.
BA3308
1pin
(40×60mm)
Fig.3
BA3308 / BA3308F
Audio ICs
4/8
!
!!
!Total application circuit
Fig. 4
BA3308 BA5406
MIC
RADIO
etc.
3.9kΩ
3.9kΩ
220Ω
39Ω
120kΩ4.3kΩ
18kΩ
100µF
330µF
0.027µF
2
8
163
7
5
4
9
L
5
8
41732
11
6
12
9
2.2µF
2.2µF
33µF
100µF
47µF
1000µF
10kΩ
10kΩ
120Ω
10µF
10µF
10
9V
0.027µF
100µF
39Ω
22µF
1MΩ
18kΩ
120kΩ4.3kΩ
L
BIAS
OSC
120Ω
33µF
47µF
47µF
0.22µF
0.22µF
470µF
470µF
2.2Ω
2.2Ω
SP
3Ω
SP
3Ω
C
C
C
A
R
A
C
B
C
B
R
A
C
A
C
C
Notes:
(1) Switches are in the playback positions.
(2) Set the values of R
A
and C
A
depending on the characteristics of the playback/recording head.
(3) The capacitor C
B
is for head resonance treble compensation during playback, and prevention of
high-frequency noise. The recommended value is about 1000pF.
(4) L and C
C
are a bias trap.
!
!!
!Circuit operation
(1) Recording
1) Recording amplifier (See Fig.5)
The channel 1 and 2 amplifier input stages of the BA3308 (pins 8 and 2) and be direct-coupled, and the input
coupling capacitors C1 and C2 are not particularly required. The voltage gain of the recording amplifier is given by
GV = R5 / R3, but as a “pop” noise is generated when power is applied, (see “operation notes”), use the time
constant circuit values given for C3 and R3 (C4 and R4) in the application example circuit diagram, or values close to
these, and adjust the voltage gain with R5 (R6). R5 (R6) is also the DC bias feedback resistor, and is connected
between pin 3 (7), and the output capacitor C5 (C6).
2) ALC (See Fig.6)
The BA3308 includes a signal rectifier block and electronic potentiometers required for the ALC. In the signal
rectifier block, a comparator compares the DC output voltage component of the output stage signal (pins 3 and 7)
to a voltage of 4.5VF (1VF is about 0.7V, so 4.5VF is approximately 3V), and if it is above this, the comparator
switches on, and changes the smoothing capacitor C7. The operating point of the amplifier’s ch1 and ch2 output
stages is fixed at 3VF, so when the signal output voltage is 1.5VF (an effective value of approximately 0.75V), the
comparator goes on, DC signals for electronic potentiometer control are generated, and the ALC starts operating.
The electronic potentiometers are connected between the input lines (pins 2 and 8) and GND, and the input signals
is attenuated by the ratio of the electronic potentiometer resistances and the external resistors R1 and R2. The
range of the ALC can be varied by the values of R1 and R2, but if they are too large the S/N ratio will worsen.
Sufficient ALC range should be obtained with R1 and R2 values of around several k ohms. C7 and R7 connected to
pin 5 set the ALC attack and recovery times. The larger the values of these constants, the longer the recovery time,
and the smaller the value of C7 the shorter the attack time.
BA3308 / BA3308F
Audio ICs
5/8
(2) Playback (See Fig.7)
During playback, the ch1 and ch2 amplifiers are used as NAB equalizer amplifiers, and time constant circuits are
connected between pins 1 and 3, and 7 and 9 in the negative-feedback section to give the NAB characteristics.
The voltage gain is given by:
G
V = | R11 + R9 / (I + jωC9 • R9) | / R3
In the same way as for recording, the NAB time constant circuit is adjusted to give the required gain (to prevent
generation of a “pop” noise when power is applied). The output stage (pins 3 and 7) operating point is fixed at 3VF.
Therefore, as indicated in the VMAX. VS, VCC characteristic (see Fig.19), even if the VCC voltage is made larger than 5V,
the maximum output voltage will not exceed 1.2V (typ.). The ALC circuit is not required for playback, so pin 5 is
grounded. The S/N ratio during playback is better if the external resistors R1 and R2 that are connected to the input
pins (2 and 8) for recording are switched out.
Fig.5
BA3308
Cont ch2
(ch1)
ch2
(ch1)
ch1
(ch2)
2 (8) 1 (9) 3 (7) 5
3.9kΩ
10µF
INPUT
39Ω
18kΩ
1MΩ
100µF
10µF
22µF
OUTPUT
R
1
(R
2
)R
3
(R
4
)
R
5
(R
6
)R
7
(R
8
)
C
1
(C
2
)C
3
(C
4
)
C
5
(C
6
)
C
7
(C
8
)
Fig.6
ch2
(ch1)
ch2
(ch1)
ch1
(ch2)
Cont
Comp
BA3308
3 (7) 52 (8)
4.5V
F
V
OUT
(DC+AC)
3V
F
R
7
C
7
R
1
(R
2
)
BA3308 / BA3308F
Audio ICs
6/8
Fig.7
A1
BA3308
2 (8)
10µF100µF
10µF
0.027µF
39Ω
4.3kΩ120kΩ
1 (9) 3 (7) 5
INPUT OUTPUT
R
9
(R
10
)
R
11
(R
12
)
R
3
(R
4
)C
5
(C
6
)
C
9
(C
10
)
C
3
(C
4
)
C
1
(C
2
)
!
!!
!Operation notes
The BA3308 has a built-in power-on mute circuit to prevent generation of a “pop” sound when the power is applied. The
generation of the “pop” sound is prevented by the DC blocking capacitors C3 and C4 connected to pins 1 and 9, and the
charge time required for the ripple filter capacitor C8 that is connected to pin 6.
To ensure correct operation of this circuit, use the values given in the application example circuit for C3, C4, R3, R4, C8 and
R8.
!
!!
!Application board component layout (component side)
(1) Recording (2) Playback
Fig.8
BA3308 BA3308
JPW
JPWJPW
R
8
R
6
R
2
R
5
R
1
R
4
R
3
R
7
C
7
C
6
C
4
C
2
C
1
C
3
C
8
C
5
R
8
C
6
C
8
C
5
R
4
R
12
R
10
R
11
R
9
R
3
C
4
C
3
C
2
C
10
C
9
C
1
BA3308 / BA3308F
Audio ICs
7/8
!
!!
!Electrical characteristic curves
Fig.9 Quiescent current vs.
power supply voltage
00246810121416
2
4
6
8
10
12
14
16
QUIESCENT CURRENT : I
Q
(mA)
POWER SUPPLY VOLTAGE : V
CC
(V)
Fig.10 Quiescent current vs.
ambient temperature
0
−50 −25 0 25 50 75 100
2
4
6
8
10
12
QUIESCENT CURRENT : I
Q
(mA)
AMBIENT TEMPERATURE : Ta (°C)
V
CC
=7V
Fig.11 Voltage gain vs. frequency
10 100 1k 10k 100k
40
0
10
20
30
50
60
70
80
90
100
GVO
VCC=7V
VOUT=300Vrms
RL=10KΩ
FREQUENCY : f (Hz)
VOLTAGE GAIN : GV (dB)
FLAT
NAB
Fig.12 Total harmonic distortion vs.
frequency
10 100 1k 10k 100k
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0 V
CC
=7V
V
OUT
=1Vrms
R
L
=10kΩ
NAB
FREQUENCY : f (Hz)
TOTAL HARMONIC DISTORTION : THD (%)
Fig.13 Voltage gain vs.
power supply voltage
0
20
30
40
50
60
70
80
90
100
2 4 6 8 10 12 14 16
R
5
,R
6
=6.8kΩ
G
VO
VOLTAGE GAIN : G
V
(dB)
POWER SUPPLY VOLTAGE : V
CC
(V)
R
5
,R
6
=39kΩ
V
OUT
=300mVrms
f=1kHz
R
L
=10kΩ
Fig.14 Closed loop voltage gain vs.
ambient temperature
0
−50 −25 0 25 50 75 100
20
40
60
80
100
120
R
5
,R
6
=18kΩ
V
CC
=7V
V
OUT
=300mVrms
f=1kHz
R
L
=10kW
CLOSED LOOP VOLTAGE GAIN : G
VO
(dB)
AMBIENT TEMPERATURE : Ta (°C)
Fig.15 Input conversion noise voltage
vs. signal source resistance
0.01 0.1 1 10 100
0.1
1
10 V
CC
=7V
G
V
=52dB
R
L
=10kW
DIN AUDIO
INPUT CONVERSION NOISE VOLTAGE : V
NIN
(µVrms)
SIGNAL SOURCE RESISTANCE : Rg (kΩ)
Fig.16 Channel separation vs.
frequency
10 100 1k 10k 100k
−40
−100
−90
−80
−70
−60
−50
−30
−20
−10
0VCC=7V
GV=52dB
VOUT=1Vrms
RL=10kΩ
Rg=0Ω
FREQUENCY : f (Hz)
CHANNEL SEPARATION : CS (dB)
Fig.17 ALC characteristics
V
CC
=7V
f=1kHz
G
V
=52dB
V
OUT
ch2 ch1
ch1
ch2
THD
−0−80 −60 −40 −20 20
−40
−20
0
20
40
60
0
10
8
6
4
2
OUTPUT VOLTAGE : V
OUT
(dBV)
INPUT VOLTAGE : V
IN
(dBV)
TOTAL HARMONIC DISTORTION : THD (%)
BA3308 / BA3308F
Audio ICs
8/8
Fig.18 Input/output characteristics
−50 −40 −30 −20
VCC=7V
f=1kHz
GV=52dB
RL=10kΩ
VOUT
THD
−60−70−80
1
10
0.1
0.01
OUTPUT VOLTAGE : VOUT (Vrms)
TOTAL HARMONIC DISTORTION : THD (%)
INPUT VOLTAGE : VIN (dBV)
Fig.19 Maximum output voltage vs.
power supply voltage
002 4 6 8 10 12 14 16
1
1.2
1.4
1.6 f=1kHz
THD=1%
R
L
=10kΩ
0.2
0.4
0.6
0.8
MAXIMUM OUTPUT VOLTAGE : V
OM
(Vrms)
POWER SUPPLY VOLTAGE : V
CC
(V)
Fig.20 Maximum output voltage vs.
load resistance
0100 1k 10k
V
CC
=7V
f=1kHz
THD=1%
2
1.8
1.6
1.4
1.2
1
0.2
0.4
0.6
0.8
MAXIMUM OUTPUT VOLTAGE : V
OM
(Vrms)
LOAD RESISTANCE : R
L
(Ω)
!
!!
!External dimensions (Units : mm)
SIP9 SOP14
BA3308 BA3308F
2.54
10.5±0.5
3.5±0.5
1
1.2
5.8
±
0.2
0.6
9
0.3±0.1
0.8
1.3
21.8±0.2 2.8±0.2
0.4
±
0.11.27
1
14
8.7
±
0.2
7
8
4.4
±
0.2
6.2
±
0.3
0.11
1.5
±
0.1
0.15
0.15
±
0.1
0.3Min.
