Here is the latest version of the schematic that I use:
A transistor and LED were added to indicate when speakers are switched off.
The whole part with RT1, RT2, T2, J1 and RLED is optional and protection module will work without them.
The C1 value may be increased if there is false activation with high output signal level from amplifier.
With these values of elements schematic will work with 24VAC, 34VDC, and will activate when there is more than ± 2VDC in output signal. Initial mute time will be around 3-4 seconds.
There are formulas in the schematic to calculate the values of the resistors for different supply voltages.
Jumper JP1 is used to set two different modes of work. If jumper is shorted the module will be in automatic resetting mode. If jumper is not connected then module will be in latching mode. For more details please read the datasheet of the uPC1237.
Bellow is a diagram how to connect speaker protection module with an amplifier.
|A little older version of the protection module.|
Here is a link for downloading an archive with PDF files of the project: DC Protection.rar
Use it on your responsibility.