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EE Design > Stereo 60W+60W RMS Power Amplifier System
Features 60W per channel into 8 ohms load at less than 0.5% THD+N from 20Hz-20KHz Signal-to-Noise Ratio >= 97dB Quiet fade-in/out mute mode Click and Pop supression SPiKe protection Compact Stereo Design Objectives The idea is to design a compact power amplifier system. The design should be simple and cost effective while maintaining the sound quality at optimal performance. It should be built modular so that the same PCBs can be simply cascaded to provide additonal 4, 6 or more output channels. The selection of the components to be integrated into the final design are carefully picked to maintain the THD+N performance. System Operation & Description The LM4780 power stereo amplifier is configured as a non-inverting amplifier which has to a gain of 20V/V which is high enough to maintain stability and not too high untill increasing the noise and THD+N performance. The input is taken from the RCA jack which then feed to two high quality 1uF metallized polyester film capacifor with 100V rating. The power output socket provides easy push-release terminals for speaker cable connections (see snap-shots picture below).  Schematic diagram taken from NS referance PCB design schematic  PCB Drawing (Not in Scale). The LM4870 power amp and the PSU (drawing left) Two 10,000uF capacitor provides sufficient buffer for the amplifier to pump and handles the bass response without distorting the output signal. A mica-sheet with heat sink compound is used in between the LM4780 and heatsink ensures proper heat transfer. A T0-3 type mica-sheet is being used because it is widely available. The heatsink is mounted vertically with its fins as shown on the snap shots below, allows heat to dissipate naturally, without the need of a cooling fan.  Full view of the power amplifier  Angle View  Abit closer  Complete side view of the power amplifier  Top view - A 125VA 24V-0-24V transformer is used  Two 10,000uF capacitor ensures there is enough buffer Upgrades & Comments A speaker protection circuit which detects faulty DC level at speaker terminals should be added to ensure speaker protection. This amplifier can be linked with the stereo pre-amplifier project for full-functional amplifier systems with digital tone and volume control. You can add an additional mono-channel 120W RMS power amplifier to drive a subwoofer, giving a 2.1 channel amplifier system. Basically the output sound quality, channel cross-talk, stability, channel gain matching are much much better than those constructed using discrete components. The overall PCB size has been reduced as more function has been integrated into the LM4780 chip. The basic protection features are also integrated, ensures total protection of the chip. With its high PSRR rating, a simple power supply design can be constructed thus reducing cost of components used in designing a well regulated power supply. Related Design Files & Materials LM4780 Datasheet |