DEF 2022 - speaker protect module

Your speakers are very expensive!

This scheme was invented by Russian engineer Ilya Stelmakh (aka NEM0), in 2016. But he is maked several changes, in 2017, 2021, 2022.
The main purpose of this module - disconnect the speaker system from the amplifier after output fault and a constant voltage appearance at its output. The circuit also implements a  connection delay of the speakers to the amplifier for 2 seconds to prevent claps when the amplifier is turned on. The disconnected state of the relay and, hence, the speakers is indicated by two red LEDs next to the relay. The power supply of the circuit can be any unipolar from 16 to 60V, with a high input voltage, a heat sink on VT1 is required. To avoid the speaker popping when switching off, it is best to power the circuit from a separate power source with small filter capacitors at the output, so that the relay turns off before the filter capacitors in the amplifier are discharged. If you use a separate +12V power supply, the VD1, VD11 and R2 elements may not be installed. In this case, the power must be connected to VCC net.
Attention! The circuit can not be used with bridge and digital amplifiers; one wire of the speaker system must be connected to GND!
Please connect contacts GNDA and GNDB to GND with separate wires in the terminal blocks, they're not connected in the schematics and PCB design. All wires marked GND (GNDA, GNDB, etc) must be connected to each other, check it many times!

UPD2 Transisitors VT13 VT23 must be bipolar, n-p-n darlington type, aka BC517, MPSA23, etc with C-E max voltage >20 Volts