Here the 68W power audio amplifier circuit which built based on single IC LM3886 from National Semiconductor.

The LM3886 is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4 load and 38W into 8 with 0.1% THD+N from 20Hz-20kHz.

Features:

Maximum Output Power   : 68W RMS - 108W Peak
THD                    : %0.03 at 60W
SNR                    : 110dB at 60 W - 92.5dB at 1W
PSRR                   : 120dB
Protection Circuitries : DC /AC Short circuit protection and thermal protection
Output Class           : Conjugate AB-A

The performance of the LM3886, utilizing its Self Peak Instantaneous Temperature (°Ke) (SPiKe™) protection circuitry, puts it in a class above discrete and hybrid amplifiers by providing an inherently, dynamically protected Safe Operating Area (SOA). SPiKe protection means that these parts are completely safeguarded at the output against overvoltage, undervoltage, overloads, including shorts to the supplies, thermal runaway, and instantaneous temperature peaks.

The LM3886 maintains an excellent signal-to-noise ratio of greater than 92dB with a typical low noise floor of 2.0µV. It exhibits extremely low THD+N values of 0.03% at the rated output into the rated load over the audio spectrum, and provides excellent linearity with an IMD (SMPTE) typical rating of 0.004%.

Download the LM3886 datasheet