ba3402 ROHM Co. Ltd., ba3402 Datasheet - Page 5

• Manufacturer Part Number: ba3402
• Description: Dual-channel, Auto-reverse Tape Preamplifier
• Manufacturer: ROHM Co. Ltd.

FElectrical characteristics curves
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 sup-
ply.
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.
If a floating input is not possible due to the construction
of the magnetic head, or wiring considerations, connect
the input via a coupling capacitor and bias the transistor
using a resistor as shown in Fig.15.
(2)
When the control pin is connected to V
channels A-1 and B-1 operate, and when it is open cir-
cuit, channels A-2 and B-2 operate. The recommended
value for the resistor is 15k .
230
Audio ICs
Input-side virtual ground
Channel switching control
CC
via a resistor,
This resistor, the capacitance of the capacitor connected
between the control pin and GND, and the 20k
down resistor on the IC determine the switching speed.
Switching speed increases as the value of the capacitor
is reduced. Set the switching speed so that it matches the
timing of the reversing mechanism. Note, that if the
switching speed is too fast, a “pop” noise will be gener-
ated. The circuit in Fig.16 illustrates how to perform chan-
nel switching by connecting the control pin to GND. Note,
that the switching speed from channel 1 to channel 2 and
from channel 2 to channel 1 is different.
(3)
In car stereos, the preamplifier output passes through the
tone control circuits before going to the power amplifier,
so it is possible to eliminate the output coupling capaci-
tors. Coupling capacitors are required when the pream-
plifier output is used directly as the deck output with no
tone control, or when it is connected directly to power am-
plifier.
Output coupling capacitors
BA3402
pull-