Thursday, March 1, 2012

Speaker protection with uPC1237

I was using IC uPC1237 for speaker protection in almost all my power amplifiers, because schematic is very easy to build with few external components.

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 R1, R2, R3, R4, Q1 and J1 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. It is also preferable if C1 is non polar (bipolar), but these are harder to find, so if it is a polar, then put one with higher voltage - at least 50V
With these values of elements schematic will work with 24VAC, 32VDC, 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.

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.

UPDATE: 29.01.2019
The link for the project files is fixed and the archive include the latest version of PCB + Gerber files.


  1. Здравей, как мога да се свържа с теб искам да поръчам една такава защита, интересуваме цена и дали ще работи при 38VDC.
    Поздрави, b0n3v :)

    1. Виж на страница "About".

    2. С голямо закъснение пиша, но човека е много точен, защитата работи коректно, без проблем вече доста месеци, добра покупка.

  2. This comment has been removed by the author.

  3. I haven't tried it yet çause I need the parts list.
    Can you please post them.

    Thanks much

  4. This is the best PCB for uPC1237 that I found on the net. It's compact and I like the way that the relay arcs to ground instead to the speaker. I built it with the same relays (RAS 1215) and it functions perfectly.


    Ivan Lukic

  5. Turn on delay and Loss of AC detection at the turn off works perfect but when I connect 9V battery to the output of amplifier protection does not disconnect the loudspeaker. I don't see any error on the PCB or schematic. How can I test if DC offset protection works properly? On my other protections when I connect 9V battery protections immediately disconnect output relay.

    1. You should test with DC voltage at the input of the protection circuit not at the output.

  6. File link for download is not valid, please re-upload again DC Protection.rar

  7. file invalid. please update the download link