INTRODUCTION
This application note describes the use of three Gennum integrated circuits, the LD502 and LC507 in recording/playback amplifiers for battery operated cassette recorders and dictaphones. A key feature of the circuits is their ability to provide excellent performance by a single battery cell. The LD502 is available in miniature MINIpac package. The LC507 is packaged in a single in-line MICROpac M4.

GENERAL PURPOSE RECORDING AMPLIFIER CIRCUIT DESCRIPTION
All the circuits described in this note comprise two gain blocks. The first block utilizes the LD502 as a microphone AGC preamplifier during recording or as a frequency compensating preamp on playback. The second block employs the LC507 as a record head driver during record ing and as a headset driver on playback.
The microphone AGC preamplifier requires only six external components including the input and ouput coupling capacitors. The initial gain is set by selecting the value of R1. With R1=130kΩ the gain is typically 40 dB for input levels up to the threshold (typically 80-100µV).
For input levels higher than the threshold, the AGC starts operating and controls the gain maintaining the output level at typically 10 mV.

FEATURES
• Operation with supply voltages from as low as 1.1V up to 6V
• Miniature packages available
• Greater than 40 dB AGC range in recording amplifier provides for constant recording level over a wide range of acoustic inputs
• Design flexibility permits minimum parts count “economy” circuits or more sophisticated version with broad smoother record/playback response