Nobsound TPA3116D2 2.1 amp. power on/off anti pop

From Ebay, I bought a Nobsound NS-08G TPA3116D2 class D Mini Digital Amplifier HiFi 2.1 with TPA3116 chips inside.

The amplifier worked OK, but the loudspeakers made loud pop sounds at power on and in particular at power off.

The amplifier front panel holds an on/off switch, that seems to control the TPA3116 output stages. At least, there is no pop sounds in switch state “off”.

In the switch on state, the center switch pin connects an input at the TPA3116 chips to ground.

With the switch in “on” state, I did measurements on the bass output while toggling the power line, yellow is bass, green is power supply:

On power up, there is a smooth pulse lasting approx. 200 msec. At power off and when supply voltage drops below approx. 7 V DC, a nasty  loudspeaker spike occurs, that makes a loud pop sound. !

I removed the on/off switch and made a circuit to delay the “on” state at power on by approx. 400 msec. and to disable the “on” state when the supply voltage drops below 10 V DC. The open collector output, pin 1 of the LM393 comparator IC2A handles up 36 V DC, and is used to enable/disable the amplifier output stages.

The SV1 MUTE pin goes to the center signal of the removed switch and SV1 pin 1 and pin 2 goes to a 5 mm white bright LED. The LED indicates the pop sound inhibitor active state and is glued into the front panel in place of the on/off switch. The LED lights up approx. 400 msec. at power up and approx. 2 sec. at power down. The numbers at at the open wire ends on the left side are the power pins of the 2 LM393D comparator ICs.


The pop sound inhibitor electronics glued in place: