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TPA3111D1: TPA3111D1 noise

Rafig Rzayev
Prodigy 40 points

Part Number: TPA3111D1

Hi,

I have one question about TPA3111D1 amplifier.


I have designed PCB according to the datasheet and evaluation board.
This is the schematic.

There is one problem with the audio system, which is noise (hum). When there is no audio signal, speaker is not silent and emits little noise. 

Initially I was powering the amplifier from a separate 12V power supply and the noise was even higher. We are using single-board computer(SBC) which is also powered by 12V. This SBC is sending the audio signal. So, I connected amplifier to SBC VDD&GND instead, and there was good progress towards decreasing the noise. But it is still present.
I was wondering what could be done in order to decrease the noise. I have read about audio ground isolators, could they be used?  
Also, I wanted to say that in our schematic FB1 and FB2 is missing at the moment and speakers are connected through P3 (not P2).
Our speaker model is: 2056-FRWS5-8OHM-ND
I would appreciate any suggestions. 
  • 0
    TI__Guru 55300 points

    Hi Rafig

      First of all, let's try to find out where this noise generated. I see we use the single ended input, the INN already connect to GND. Lets' also connect INP to GND, short the Header P1's pin1 and pin2 is fine, and check out if there's still noise.

        If the noise still there, please capture the waveform at P2 and P3. Also check the waveform of your PVCC. Let's see if the output has this noise directly, or it comes from power supply.

  • 0 in reply to Shadow He
    Prodigy 40 points

    Hello.
    Thank you for your reply
    I tried what you say about shorting the pin1 and pin2 and after this there is no more noise.

  • 0 in reply to Rafig Rzayev
    TI__Mastermind 19860 points

    Hi,

    You short pin 1 and pin 2 of Header, right?

    If so, the noise is from audio source, not AMP device.

  • 0 in reply to Yanming Gong
    Prodigy 40 points

    Hi,

    I solved the noise problem by adding a capacitor (0.1uf - 1uF) between INN and INP header.

    But I also have a POP noise problem while device is turning ON and turning OFF.

    I tried to change 1uF capacitors on INN and INP pins for larger and smaller capacitance. But that did not help. Pop noise is still present.


    Could you give some advice to solve the POP noise problem?

    Thank you

  • 0 in reply to Rafig Rzayev
    TI__Guru 55300 points

    Hi Rafig

       You can try pulling SD pin low first when power on and off. Wait the power supply to be stable until you release the SD pin, doing this will decrease the pop.

  • 0 in reply to Shadow He
    Prodigy 40 points

    Hi
    Thank you for your reply.


    I tried it and when I release SD pin from low state It still Pops.

    And when any processes occur in my Single-board computer (SBC), it creates pops depending on any processes that go to the SBC.

    Now I use a MOSFET to turn on the amplifier 30 seconds after the system starts up. This is how I solve the first POP noise while the SBC turns on. But in the future, during the operation of the SBC, there are POP noises


  • 0 in reply to Rafig Rzayev
    TI__Guru 55300 points

    Hi Rafig

       I'm not sure why there's a connection between your SBC and our amp, maybe your SBC working create the noise signal into the input wire. How about we capture the waveform at both input and output side to observe this pop signal?

  • 0 in reply to Shadow He
    Prodigy 40 points

    AMP is connected to SBC in order to amplify the signal coming from SBC and to send it to speaker. In other words we add "custom" sound system to SBC. Please see the diagram below:

    It looks to me that root issue is somehow related to Vdd/GND lines. For your reference, page 26 of the schematics shows audio connection on SBC: https://dl.radxa.com/rockpi4/docs/hw/rockpi4/rockpi4_v13_sch_20181112.pdf

    As for the noise, in order to elaborate, we can say that there are two kind of strange noises:

    • SBC activity noise
      • When SBC is computing, opening programs(electric load on SBC changes), we get strange varying noise on speakers. When audio is being played(eg Youtube, audio file), this noise disappears while audio is on. This noise is removed by adding a capacitor between INN and INP, but it slightly decreases speaker volume. We can use this method, but not sure if it is ok. Plus it would be great not to compromise volume in order to remove the noise. 
    • Audio start pop noise
      • Whenever we start playing audio on SBC, in the moment when audio stream starts, we get pop noise. In other words, once audio codec on SBC understands that it will start streaming, some transition happens, and we get a pop noise. We are using voice assistant application on our system. Before each talk of voice assistant we are getting this pop noises. We don't know how to remove this one.
  • 0 in reply to Shadow He
    Prodigy 40 points

    This is the waveform for Input and output signals during turning off

    https://files.fm/u/5h8yhhpmu

    You can watch the videos 

  • 0 in reply to Rafig Rzayev
    TI__Guru 55300 points

    Hi Rafig

       Seems that the video is blocked by our companies' IT policy. But according to your descriptions, it's highly possible that both of your noise is coming from your SBC. If the power supply is causing the problem, the noise should be larger when you play audio. But you can also try to use oscilloscope to observe the power supply condition to make sure. But more importantly, is to observe the SBC's pin3 and pin2 output, capture the noise waveform, and do some FFT analysis to know what frequency of this noise, then try to find out the root cause. If the problem is inside of SBC, I'm afraid we can't help too much here.