LA4160 TAPE RECORDER AND PLAYER

INTRODUCTION:

In this Instructables I am going to introduce a Single Chip Tape Recorder Circuit. I got this circuit from an old PHILIPS Radio. This Circuit is build around LA4160 IC which is very famous for single chip tape recorder system. This IC (Integrated Circuit) is manufactured by Sanyo Corporation.

The preamplifier circuit consists of the input differential stage (TR9, 10), level shift stage (TR13), and output stage (TR17, 18, 19). Since the output stage is of push-pull type, no remarkable drop in the output voltage occurs even at low load impedances and the output can be connected direct to the ALC circuit and meter circuit. The external DC/AC feedback resistor (Z2) can be set arbitrarily and the closed loop gain is obtained by the following equation.

Since oscillation may occur when used at a low voltage gain, a capacitor of approximately 10pF must be connected across pins (8) and (6) for phase compensation. If the capacitor connected across pins (8) and (6) has a large capacitance at a low load impedance, further oscillation may occur, and in this case the load pin must be grounded through a capacitor of approximately 0.01µF (Polyester film capacitor). The input pin must be grounded through a capacitor of approximately 1000pF for the purpose of prevention of radio disturbance and oscillation.

The ALC circuit is of Darlington configuration which consists of TR1, 2. The collector-to-emitter impedance of TR1 made variable by the DC voltage to be applied to control pin (5) and the input voltage of the preamplifier is controlled. When the DC voltage to be applied to pin (5) is set at approximately 1.1V, TR1, 2 are turned ON and ALC is turned ON. For the rectifier circuit, it is recommended to use the voltage doubler rectifier which is excellent in compression ratio. For the sets of 6V VCC, it is recommended to use a germanium diode so that the ALC width can be made wider even at the time of decreased voltages.

The power amplifier circuit consists of the differential stage (TR22, 23), pre driver stage (TR41), driver stage (TR42, 44), and output stage (TR47,48). Bias resistor R36 of TR20 at the first stage is attached externally and the input impedance depends on this R36. Input pin (4) whose potential is nearly equal to the ground potential can be connected direct to the variable resistor without using an input coupling capacitor. The closed loop voltage gain is obtained by the following equation,

For the oscillation preventing capacitor connected across output pin (1) and ground, it is recommended to use a polyester film capacitor which is excellent in temperature characteristic and frequency characteristic. It should be noted, however, that if such a polyester film capacitor as to have a resonance point at a high frequency is used oscillation may not be prevented.