BA3308FV 查看數據表（PDF） - ROHM Semiconductor

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BA3308FV

Preamps with Built-in ALC

ROHM Semiconductor 

BA3308F,BA3308FV

●Description of operations

1. Recording

1) Record amplifier

The BA3308F/FV amplifier of ch1 and ch2 input stage

(13pin, 9pin) can be direct coupled or use coupling

capacitors (C1/C2). The voltage gain of the record amplifier

is determined by GV=R5/R3. The R5/R6, and C3/R3 regulate

control of the pop noise that occurs at power-on (see

“Cautions on use”) and direct current bias fed back is set by

R5/R6 and C5/C6 at the output stage.

Technical Note

BA3308

13(29)(8)

11(101) (9)

R1

(R2)

3.9k

C1

(C2)

10F

INPUT

R3

(R4)

39

C3

(C4)

100F

Cont

ch1

(ch2)

ch2

(ch1)

ch2

(ch1)

R5

(R6)

18k

31 (7)

C5

(C6)

10F

45

C7

(C8)

22F

R7

(R8)

1M

OUTPUT

FiFgi.g1.45

2) ALC

The BA3308F/FV has an on-chip signal rectifier and electronic

volume needed for ALC. The signal rectifier compares the direct

current output voltage that is superposed in the output stage (1, 7pin)

signal to the reference voltage 4.5VF (≒3V; 1VF is approximately

0.7V) in the comparator circuit and if the output voltage is higher, it

turns the comparator ON to charge the smoothing capacitor C7.

Since the operation point of the output stage of amplifier ch1 and ch2

is fixed at 3VF, the comparator turns ON when the peak value of the

signal output voltage is 1.5VF (effective value approx. 0.75V). Once

the direct current signal for electronic volume is controlled, ALC VOUT (DCAC)

operation starts. The electronic volume, which is connected between

the input line (13, 9pin) and GND, causes the input signal to 3VF

attenuate according to the ratio of the external resistance (R1, R2) to

the resistance value of the electronic volume. The ALC range varies

according to the values of R1 and R2. For small ALC variation the

S/N will determinate an adequate ALC range is obtained by applying

several kΩ of the R1 and R2. The attack time and recovery time of

ALC are set according to C7 and R7 of 4pin. If the time constants

(C7, R7) are large, the recovery time will be long and as C7 becomes

smaller, and the attack time will be shorter.

ch1

(ch2)

4.5VF

1 (7)

3 (7)

ch2

(ch1)

ch2

(ch1)

Comp

Cont

BA3308

4

13(9)

5

2 (8)

R7

C7

R1

(R2)

Fig.15

Fig.6

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© 2010 ROHM Co., Ltd. All rights reserved.

2010.04 - Rev.A

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