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LM4880: Pop noise to mute and unmute thought shutdown pin

Part Number: LM4880
Other Parts Discussed in Thread: NE5532, TPA6139A2, TPA6138A2

I'm trying to implement a pop-free circuit with the LM4880 that is connected to a 10 ohm headphone. I use the LM4880's shutdown pin to mute and unmute but I'm getting a lot of pop when the state of this pin is changed.

The circuit is composed of a DAC, the NE5532 (buffer) and the LM4880. The buffer is supplied with +/-5V and works with a band-pass filter through the decoupling capacitors (C45, C46, C52, C53, C55, C56). The LM4880 is powered with 5V and has inverted unity gain and a 330 uF output capacitor (CP3 and CP4) and 10 uF bypass capacitor.


What I've already tried to do:
  1. Changing the LM4880 bypass capacitor from 10 uF to 100 uF: no sigficant change
  2. Changing buffer DC decoupling capacitors (NE5532) from 22 uF to 1 uF: no significant change
  3. Changing the LM4880 bypass capacitor from 10 uF to 1 uF: no significant change is heard, just a change the output speed to archieve Vdd/2
  4. Removal of the 2 kohm stabilization resistors from the LM4880: there was no change
  5. Removed the capacitor from the mute circuit: there was no change

Any ideia how can I solve the problem?

Best regards.

  • Hi Rafael,

    Have you locked the decision of using LM4880 in your application?
    Perhaps you can consider using newer devices such as TPA6138A2 / TPA6139A2, which feature GND-centered outputs helping with output AC coupling cap and pop.

    For debugging on your system, I would suggest isolate the headphone amp first by shorting the inputs of LM4880 to GND, you may do this before the input AC coupling caps, then check how the different component changes affect the performance. Usually, pop is caused due to impedance mismatch at inputs and charge/discharge of capacitors through the signal path. Using low tolerance components is recommended.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • TPA6138A2 / TPA6139A2 don't support 8ohms load

    I shorted the inputs of LM4880 to GND before the input AC coupling caps and still pops Disappointed

    Also tried to connect the LM4880 directly to the DAC, bypassing the buffer (NE5532), still pops.

    Any suggestions?

    Best regards.

  • Hi Rafael,

    Does changing the value of the output coupling capacitors helps?
    I just realized your load impedance is 10Ω, I'll check if there's any alternative we can suggest for such conditions.

    Best regards,
    -Ivan Salazar
    Applications Engineer