193
Audio ICs
Dual preamplifier with ALC
BA3308 / BA3308F / BA3308FV
The BA3308, BA3308F and BA3308FV 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), 14-pin MF
(BA3308F) and 14-pin SSOP (BS3308FV) 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 capaci-
tors. 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 =
4.5V 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 = 25C)
Recommended operating conditions (Ta = 25C)
194
Audio ICs BA3308 / BA3308F / BA3308FV
Block diagram
Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 7.0V, f = 1kHz and BPF: 20Hz to 20kHz)
195
Audio ICs BA3308 / BA3308F / BA3308FV
Measurement circuit
Application example Application example circuit PCB (copper side)
196
Audio ICs BA3308 / BA3308F / BA3308FV
Total application circuit
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) can be direct-coupled, and the input cou-
pling 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 ap-
plication 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 be-
tween pin 3 (7), and the output capacitor C5 (C6).
(2) ALC (See Fig. 6)
The BA3308 includes a signal rectifier block and elec-
tronic 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 charges 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 poten-
tiometer control are generated, and the ALC starts oper-
ating.
The electronic potentiometers are connected between
the input lines (pins 2 and 8) and GND, and the input sig-
nals is attenuated by the ratio of the electronic potentiom-
eter 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. Suf-
ficient ALC range should be obtained with R1 and R2 val-
ues of around several kohms. 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.
197
Audio ICs BA3308 / BA3308F / BA3308FV
(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 nega-
tive-feedback section to give the NAB characteristics.
The voltage gain is given by:
GV = R11 R9/ (I jϖC9 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.
198
Audio ICs BA3308 / BA3308F / BA3308FV
Operation notes
The BA3308 has a built-in power-on mute circuit to pre-
vent generation of a “pop” sound when the power is ap-
plied. 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)
199
Audio ICs BA3308 / BA3308F / BA3308FV
Electrical characteristics curves
External dimensions (Units: mm)
200
Audio ICs BA3308 / BA3308F / BA3308FV
Product Designation Page 1 of 2
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Product Designation
lWhen ordering, specify the part number.
lCheck each code against the tables shown below.
lFill in from the left, leaving any extra boxes empty on the
right.
Product Designation
Ordering information
Packing and forming information only required for SOP, and QFP
parts that are required in tape and reel containers. For example,
to order part BA4558F on paper tape type E2, order number is
BA4558F-E2, when required in tube container, order number is
BA4558F.
Quick reference of packaging specifications
Package Container
type Packaging
specification code
DIP/SDIP Tube
container
SIP/HSIP/ZIP/SZIP/RSIP-A3 Tube
container
SOP/SSOP/HSOP/WSOP-10/WSOP-
L10
Tube
container
Embossed
tape E1, E2
Product Designation Page 2 of 2
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[LSI Package Assemblies]
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SSOP-A54 Embossed
tape E2
QFP/SQFP/VQFP/UQFP/TQFP/PBGA
Tray
Tray (dry
pack) VP
Embossed
tape E1, E2
TO220FP Bulk
Tube
container
SMP5 Embossed
tape TL, TR
TO252 Embossed
tape E1, E2
RSLP8 Embossed
tape E2(Sprocket 1pin,
Horizontal)
RSIP13 Embossed
tape
E2(Sprocket 1pin,
Horizontal), E4
(Sprocket 1pin,
Vertical)
Note: SOP type can be delivered in tube, paper tape, or embossed tape.
BGA/CSP package |SIP/ZIP package
QFP package |Photo package
SOP package |Product Designation
DIP package |Packaging Specification
