The ε12 muting / protect circuit

Project history

There are many muting delay and DC offset protection circuits published for speaker amplifiers, but I have not found one that is sensitive enough for a headphone amplifier. Also, it would be nice if such a circuit could support a wide range of different amplifier designs, including those with active ground outputs and fully-differential balanced outputs.

I often hear people complain about their amplifiers' turn-on "thump" noise. Also, in some instances expensive headphones have been damaged, either by the transient or by excessive DC offset during a circuit malfunction. This calls for a proper muting delay and protection circuit specifically for headphone amplifiers (and applicable for pre-amplifiers, too).

In late 2004 I decided to design just such a circuit and to share it with others in the DIY community. One goal I had was to keep the parts count and cost reasonable. After several revisions of the schematic, I built a prototype on breadboard for testing. A few more minor optimizations were then made. I announced the design in early May 2005 on the DIY forum.


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