I am using TPA2005D1 class D amplifier IC, whenever I am turning ON the IC, while the volume is set to high, it is making loud thump and pop sound, then it goes away and works fine. But while the volume is set to low and then I turn ON the device, then is no thump and pop sound.

The line level input that I am giving to TPA2005D1 contains small DC offset, but I am using coupling capacitor to make offset zero. (Please find the schematic attached below)

enter image description here

After getting the response from the users I am finding two approaches to solve this problem.

Method 1: Can we connect 100K resistor between C15 and ground ; 100K between C16 and ground, so that there is no buildup of charge in the capacitor as to reduce the pop sound in the first place.

Method 2:

We can delay the start of the TPA2005D1 using RC circuit in the shutdown pin, so that pop sound will be eliminated.

Should I do Method 1 or Method 2?

  • 1
    \$\begingroup\$ Some amps have a « soft start » to avoid this issue. Comes with quality and price.... \$\endgroup\$
    – Solar Mike
    Apr 3, 2018 at 9:57
  • \$\begingroup\$ How to avoid this issue when the using the amplifier which do not have soft start, using design change (adding cap and bleeder resistor) \$\endgroup\$
    – TapasX
    Apr 3, 2018 at 10:04
  • \$\begingroup\$ You did not ask that question originally .... So edit your circuit to gradually ramp up the input on start... \$\endgroup\$
    – Solar Mike
    Apr 3, 2018 at 10:08
  • \$\begingroup\$ The usual approach is to put a time delay on the shutdown pin. Something like (not tested!) a capacitor to ground, such that R27 * C = 1 second or so. And a diode (normally reverse biased) in parallel with R27 to discharge the C when the power goes off. \$\endgroup\$
    – user16324
    Apr 3, 2018 at 11:04
  • \$\begingroup\$ @BrianDrummond, I am planning to use RC delay in the shutdown pin. I am wondering do we need Schmitt trigger to ensure stability. Or Just by using RC delay the problem of the pop sound will be solved. \$\endgroup\$
    – TapasX
    Apr 3, 2018 at 13:21

1 Answer 1


A thump on startup of a audio system is usually due to DC offsets settling.

For example, consider a amplifier that works on a single 12 V supply. Internally, the quiet level is a flat 6 V. However, when the circuit is first turned on, that 6 V node starts at 0 V. During the time the system is stabilizing, it can look like there is a large 6 V signal. Depending on what order various parts power up in, that can produce a "thump" sound in the output.

There are various ways to deal with this. Some systems deliberately delay the power up of the final output drivers. I've even seen relays on the outputs of a high power amp. Those delayed connecting the speakers until the amp circuitry had settled.


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