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TPA2006D1: Noise in Amplifier output with no audio input

kiran habib
Prodigy 120 points
Part Number: TPA2006D1

Hi,

We are using the above amplifier in a speakers(2x8ohm @ 1watt).

The output of speaker amplifier is connected to common mode Inductor( SRF2012-121YA).

We could hear a noise sound in speakers without any audio input. Below are the waveforms captured at the output of amplifier.

Kindly let us know how we could rectify this issue.

Fig 1 : Amplifiers output waveform.

Fig 2 : Magnified version of Fig 1.

Thanks & Regards,

Kiran

  • 0
    TI__Guru** 101795 points
    Hi Kiran,

    Does removing the inductor eliminates the noise?
    Could you share the connections of the output of the amplifier? Perhaps you could change the common-mode inductor for a ferrite-bead/capacitor filter.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    Intellectual 270 points

    Hi Ivan,

    I'm kiran's colleague. Removing the inductor did not eliminate the noise.

    We tried different combinations of ferrite-bead/capacitor filter, but couldn't find a positive outcome.

    Attached the schematics for your reference. (note: Interchanging R108 & C75 did not make any difference in the noise level).

    Please let us know ways to eliminate this noise.

    Regards,

    Gireesh

  • 0 in reply to Gireesh Nair40
    TI__Guru** 101795 points
    Hi Gireesh,

    Do you have captures of the inputs?
    Could you try to short both inputs to GND? Or just short both inputs between them (not to GND)? This way the output should be affected only by the amp.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    Prodigy 120 points

    Hi Ivan,

    We tested by shorting both inputs of amplifier to ground, we could see a noise reduced to a great extend.

    Could you let us know what value of RC should be use to allow a good amount filtering when inputs are connected.

      Current values are R=20.5KOhm C =3.3nF.

    Thanks & Regards,

    Kiran

  • 0 in reply to kiran habib
    TI__Guru** 101795 points
    Kiran,

    I just noticed that the label of the input to TPA2006D1 is called "codec", so am I right to assume this is the output from a DAC?
    If that's the case, I would recommend to add an RC Low-Pass Filter before the DC coupling input capacitor and the input resistor. Calculate the value of the LPF components to that the cutoff frequency is around 22kHz, in case you're using the whole audio bandwidth.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    TI__Guru** 101795 points
    Kiran,

    Have you tried with the LPF filter as mentioned above?
    Are there still any questions?

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    Intellectual 270 points

    Hi Ivan,

    We tried placing LPF as you have mentioned, below are the details of the same. But we couldn't find a significant reduction in the noise by using this LPF. Please review the LPF circuitry we have used and let us know if we need to modify anything.

    LPF:

    RC filter: R=1K , C=6.8nF , Cutoff Frequency=23.4Khz

    --

    Regards,
    Gireesh

  • 0 in reply to Gireesh Nair40
    TI__Guru** 101795 points
    Gireesh,

    By shorting the inputs the noise was reduced, as you tested before. So the noise is not being caused by the amp itself, you should inspect your system to look for the source of the noise.
    That jitter at the output could be caused by noise at the input or perhaps at VDD source voltage.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    TI__Guru** 101795 points
    Gireesh, Kiran,

    Do you have further updates on this? Were you able to identify the source of the noise at the inputs of the device?
    Did you tried to connect a different audio source to evaluate performance?

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators