ba3304f ROHM Co. Ltd., ba3304f Datasheet - Page 4

• Manufacturer Part Number: ba3304f
• Description: Dual Preamplifier
• Manufacturer: ROHM Co. Ltd.

FOperation notes
(1)
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 transis-
tor 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)
With the BA3404F, a capacitor must be connected be-
tween each input pin and the bias pins to prevent oscilla-
tion and RF mixing. The recommended value for this ca-
pacitor 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 au-
dio frequency characteristics. These capacitors can also
be used for treble compensation. Determine the value
based on the relationship with the magnetic head imped-
ance.
(3)
The capacitor connected in series with the gain-setting
resistor between the NF pin and the bias pin, is the by-
pass capacitor. The value of this capacitor determines
the bass characteristics
(4)
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 closed-
loop gain of G
of the circuit components is given by the following equa-
tions:
Audio ICs
Input-side virtual ground
Capacitor for prevention of oscillation and RF mix-
ing
Bypass capacitor
Playback equalizer(NBA)
VC
(dB) at a frequency of 1kHz, the value
The recommended value for R
large, the voltage gain will not match the calculated val-
ue.
(5)
The BA3304F has an emitter-follower output, so oscilla-
tion is apt to occur if the load is capacitive (if the capaci-
tance of the load exceeds 150pF with V
will occur). Oscillation is apt to occur if the closed-loop
gain (G
cially 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)
Performance degradation due to input / output interfer-
ence is related to the amplifier gain, the amount of feed-
back 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 recom-
mend that you separate the virtual earth for the input and
output components, and have one earth at the bias pin.
(7)
(a) Power supply
To avoid possible destruction of the IC, before connect-
ing the power supply pins to the PCB, ensure that there
are no shorts due to solder bridges, and take care to en-
sure that the polarity is correct.
(b) Static
Static electricity that accumulates on the clothing of oper-
ators and on belt conveyors can range from thousands
to tens of thousands of volts. To prevent damage to com-
ponents due to static discharge, ensure that all operators
and conveyor belts are earthed.
Capacitive loads
Input / output interference
Assembly precautions
VC
R
R
C =
) is lower than 30dB at f = 1kHz. Caution is espe-
2
1
= 15.6 R
=
3180 10
53
2
R
2
R
3
2
* 6
10
Gvc / 20
3
is about 100 . If R
( )
( )
(F)
CC
= 3V, oscillation
BA3304F
3
is too
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