GK509

The GK509 is a Class A amplifier utilizing Gennum's proprietary low voltage JFET technology. It consists of a single-ended, low noise inverting gain block, a Class A output stage, an on-chip microphone decoupling resistor, and a pair of Schottky diodes for symmetrical peak clipping.

Block A typically has an open loop voltage gain of 56 dB, with the closed loop gain set by the ratio of thefeedbackresistor to the source impedance. It is recommended that the maximum closed loop gain be 20 dB lowerthan 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 duringchangesinvolume control settings.

The output stage of the GK509 is a Class A current drive. It has a fixed reference voltage of typically 30 mV at pin 2 of the device. The current that flows in the transducer is the ratio of the 30 mV reference voltage and the on-chipemitter 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 GK509 also contains a pair of Schottky diodes in the feedback configuration of the output stage, which providesapproximately 12 dB of MPO control.