Portable bluetooth speaker audio amplifier! noise problem, tips needed

Discussion in 'The Projects Forum' started by kaning, May 2, 2015.

  1. kaning

    Thread Starter Member

    Jun 2, 2014
    43
    0
    Hi all,

    Im using a pam8403 2x3w module audio amplifier and BLK-MD-SPK-B bluetooth module receiver (datasheet here). for this thread sake i've made a simple schematic to show you the problem im having. last time i built this schematic (last summer) this noise was not ocurring.

    I've been reading a lot and search about possible solutions, like proper grounding, wich i dont think its the case. anyway its my first audio project and im quite newbie in handling audio signals. i've tried several other things but with no success, here is a demonstration.



    how it looks on the breadboard.

    http://imgur.com/8wPVbMV

    http://imgur.com/5hCNz9J

    the only diference from theese pictures is that im using a 100uf capacitors on both battery and 1.8v output. also tried to to add extra cap more near the bluetooth pins but nothing changed.

    important note: this problem is somehow connected to bluetooth module because without it you can only hear small "ch" noise, when bluetooth module connected to phone and amplifier you hear whats in the video. many thanks in advance.
     
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
    368
    Sounds like data. Have you tried running the BT module from its own power supply or moving it further away from the amplifier?
     
  3. kaning

    Thread Starter Member

    Jun 2, 2014
    43
    0
    with diferent power supplies the "data noise" disappears and only small "ch" sound remains. anyway, for some reason with diferent power supplies the sound
    stutters. both 3,7 lipo battery.
     
  4. kaning

    Thread Starter Member

    Jun 2, 2014
    43
    0
    after some testing i got to the following conclusions.
    - the "ch" sound comes from amplifier. just by powering amplifier with battery it starts. (solved)
    - both bluetooth and amplifier module work perfect when using them individualy.
    - using separated batteries for each module the "data sound" disappears.
     
    Last edited: May 4, 2015
  5. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
    368
    It may not be possible to fully resolve the issues while the circuit is built on breadboard as the connections will be longer and have a much higher impedance than if it built were on a PCB. You have to be very careful when designing the layout of circuits that combine both analogue and digital (and in this case RF) elements.

    Other things to try; Solder 100n decoupling capacitors as close as possible and directly across the power supply pins of the modules, add ferrite beads to the power supply lines (close to each moduel), separate audio/analogue 0V from power and digital 0V so there can be no power or digital currents flowing in the audio 0V.
     
    Last edited: May 5, 2015
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