This circuit is a universal protection module for low-frequency audio amplifiers. It provides delayed connection of the speakers at power-on (approximately 5 seconds), preventing unwanted transients until the amplifier’s DC operating point stabilizes.
When the power supply is switched off, the speakers are immediately disconnected from the amplifier output. If a DC voltage appears at the amplifier output due to a fault (short circuit, output transistor failure, etc.), the protection disconnects the load regardless of the voltage polarity.
The turn-on delay time and the DC fault trigger threshold are adjustable. The circuit is designed to operate with a supply voltage in the range of 12-20 V DC. Two supply inputs are provided - U1 (rectified and filtered, optionally stabilized) and U2 (rectified only).

Technical Specifications:
Type: low-frequency amplifier protection.
Functions: delayed turn-on, fast turn-off, DC protection.
Turn-on delay: approx. 5 s.
Adjustments: turn-on delay time and DC protection threshold.
Supply voltage: 12-20 V DC.
Supply inputs: U1 (rectified and filtered), U2 (rectified).
PCB dimensions: 45 x 29 mm.

This product is a DIY assembly kit.