Thumpless turn-on mod for Tripath amps

Most of us know about the huge thump you hear from your speakers when you switch on the power to most Tripath amps. That can be eliminated by incorporating a simple circuit into your Tripath amp.

I had an original SI laying around so that's the amp I've been using to test my circuit. This mod requires you to lift the Fault pin of the chip and install a wire to run to the circuit. In the attached photo you can see the pin which needs to be lifted and the via through which I installed the wire. You will need to enlarge to hole before you can get cat5 gauge wire through the hole. You could just tack it to the pad of the lifted pin but it's more secure if you put it through the via.

This is a photo of the opposite side of the board where I soldered the wire. You need scrape the solder stop off the via before soldering. An x-acto knife or sharp tweezers work well for this.

The circuit uses a 555 timer to provide a delayed turn on signal (can change length of delay by changing the values of R3 and C4) to the mute pin of the amp. Attached is the schematic of the delay circuit. Vdd is the 12-14V supply and MUTE goes to the mute pin of the Tripath chip.

Edit: You don't actually need R4 for the circuit to work properly. It works great even with repeated turning on and off of the power supply. All you hear is a little click from the speakers when the chip unmutes the output stage.