LS509_1235230

The LS509 is a Class A amplifier utilizing Gennum's proprietary low voltage JFET technology. It consists of two singleended, low noise inverting gain blocks, a Class A output stage, an on-chip microphone decoupling resistor and a pair of Schottky diodes for symmetrical peak clipping. Blocks A and B typically have an open loop voltage gain of 56 dB, with the closed loop gain set by the ratio of the feedback resistor to the source impedance. It is recommended that the maximum closed loop gain be 20 dB lower than the open loop gain. All blocks of the device are internally bias compensated, preventing any DC current flow via external feedback resistors. Without this compensation, audible scratchiness would be present during changes in volume control settings.

The output stage of the LS509 is a Class A current drive. It has a fixed reference voltage of typically 29 mV at pin 2 of the device. The current that flows in the transducer is the ratio of the 29 mV reference voltage and the on-chip emitter resistor (RE). To increase the bias current in the transducer, simply place an external RE resistor from pin 2 to ground, thereby decreasing the equivalent emitter resistance and increasing the current.

The LS509 also contains a pair of Schottky diodes in the feedback configuration of the output stage, which provides approximately 12 dB of MPO control. VB