The NTE1850 is a dual HiFi audio power amplifier in a 9Lead SIP type package designed for mainsfed applications such as stereo TV sound and stereo radio. The circuit is optimal for symmetrical power supplies but is also well suited to asymmetrical power supply systems. An output power of 2 x 12W (THD = 0.5%) can be delivered into an 8 load with a symmetrical power supply of 16V. The gain is fixed internally at 30dB, but can be changed externally if required. Internal gain fixing gives low gain spread and very good balance between the amplifiers (0.2dB). A special feature is an input mute circuit which provides suppression of unwanted signals at the inputs during switching on and off. This circuit disconnects the noninverting inputs when the supply voltage is below 6V, while allowing the amplifiers to remain in their DC operating condition. Two thermal protection circuits are provided, one monitors the average junction temperature and the other the instantaneous temperature of the power transistors. Both protection circuits activate at +150C, allowing safe operation to a maximum junction temperature of +150C without added distortion. Applications: