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Audio ICs
3V dual preamplifier
BA3304F
The BA3304F is a monolithic, dual-preamplifier IC designed for 3V applications. It has been designed especially for lowvoltage operation. The preamplifiers can be directly coupled to the head to minimize the "pop" noise at power on. When combined with the Rohm BA5204, it is a simple matter to design a high-performance circuit for cassette players.
FApplications 3V headphone stereos, 3V micro-cassette players and low-voltage stereo equipment
FFeatures 1) Low noise (VNIN = 1.2Vrms). 2) Input coupling capacitors not required. 3) No input coupling capacitors means high bass stability. 4) Good channel balance.
5) Built-in bias circuit minimizes "pop" noise. 6) Emitter-follower output for low output impedance. 7) Good low voltage characteristics (operation possible from Typ. 1.2V).
FBlock diagram
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Audio ICs
FAbsolute maximum ratings (Ta = 25_C)
BA3304F
FInternal circuit configuration
FDescription of circuit (see Fig. 1) As shown in the equivalent circuit for the BA3304 in Fig. 1, the first stage is a differential amplifier. This gives good stability with respect to temperature and supply voltage variation, and improves resistance to earth and power supply noise. The second stage uses Darlington pairs to increase the input impedance and the gain of the first stage. The output is an emitter follower which suppresses deterioration of the linearity due to the influence of the equalizer terminal, and prevents drop in maximum output.
FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 3V, f= 1kHz and RL = 10)
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Audio ICs
FMeasurement circuit
BA3304F
FApplication example (Fig. 3) C1 and C2: Capacitors for prevention of oscillation and RF mixing The recommended value is 100pF. If the value of the capacitors is too small, oscillation and RF noise due to strong RF signals can degrade circuit performance. If the value of the capacitors is too large, the audio frequency characteristics will deteriorate. C3: Filter capacitor The recommended value is 47F. The startup time after power is applied is related to the value of this capacitor. If the value of the capacitors is too small, transient noise when power is applied will be large.
C4 and C5: Bypass capacitors The recommended value is 47F. The time constant of the circuits formed by these capacitors and the resistors R1 and R2 determines the bass cutoff frequency. R1 to R6, and C7 and C8: equalizer terminal (NAB) These components set the time constant for normal tape (120s), and the tape speed to 4.75cm / s. The gain is 33dB at 1kHz.
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Audio ICs
FOperation notes (1) Input-side virtual ground If coupling capacitors are used to connect the head with the preamplifier input, the capacitor charging current flows in the head and can magnetize it. To prevent this, a virtual ground is used on the input side, and coupling capacitors are not required even with a single-rail supply. This is the bias pin input and the virtual ground point for the negative feedback, and the bias for the input transistor is taken from this terminal. The only DC current that flows in the magnetic head is the base bias current for the input transistor, which is not enough to magnetize the head. (2) Capacitor for prevention of oscillation and RF mixing With the BA3404F, a capacitor must be connected between each input pin and the bias pins to prevent oscillation and RF mixing. The recommended value for this capacitor is 100pF. If it is too small, oscillation and RF noise can adversely affect circuit performance. Conversely, if the value of the capacitor is too large, it will affect the audio frequency characteristics. These capacitors can also be used for treble compensation. Determine the value based on the relationship with the magnetic head impedance. (3) Bypass capacitor The capacitor connected in series with the gain-setting resistor between the NF pin and the bias pin, is the bypass capacitor. The value of this capacitor determines the bass characteristics
BA3304F
R2 = 15.6 R1 = 2 53
R3 R2
10Gvc / 20
() ()
C=
3180 10*6 R2
(F)
(4) Playback equalizer(NBA) The playback equalizer characteristics are determined by the RC circuit connected between the output pin and the NF pin. For the circuit shown in Fig. 4, with a closedloop gain of GVC (dB) at a frequency of 1kHz, the value of the circuit components is given by the following equations:
The recommended value for R3 is about 100. If R3 is too large, the voltage gain will not match the calculated value. (5) Capacitive loads The BA3304F has an emitter-follower output, so oscillation is apt to occur if the load is capacitive (if the capacitance of the load exceeds 150pF with VCC = 3V, oscillation will occur). Oscillation is apt to occur if the closed-loop gain (GVC) is lower than 30dB at f = 1kHz. Caution is especially required with long lengths of thin shielded wire. If use of a large capacitive load cannot be avoided, connect a resistor of a few hundred ohms in series with the load. (6) Input / output interference Performance degradation due to input / output interference is related to the amplifier gain, the amount of feedback from the output to the input, and amplifier phase rotation. Care is required to avoid component layouts that will cause input / output interference when high gain is used. With regard to component layout, we recommend that you separate the virtual earth for the input and output components, and have one earth at the bias pin. (7) Assembly precautions (a) Power supply To avoid possible destruction of the IC, before connecting the power supply pins to the PCB, ensure that there are no shorts due to solder bridges, and take care to ensure that the polarity is correct. (b) Static Static electricity that accumulates on the clothing of operators and on belt conveyors can range from thousands to tens of thousands of volts. To prevent damage to components due to static discharge, ensure that all operators and conveyor belts are earthed.
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Audio ICs
FElectrical characteristics curves
BA3304F
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Audio ICs
FExternal dimensions (Units: mm)
BA3304F
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