1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Disturbing sound is coming from Bluetooth audio amplifier

Discussion in 'General Electronics Chat' started by learning, Sep 14, 2017.

  1. learning

    learning Member

    Joined:
    Dec 9, 2008
    Messages:
    179
    Likes:
    1
    Location:
    Kolkata,India
    Please give me a suggestion for rectifying the humming sound which is coming from my Bluetooth audio system. It is increasing after 15-minute power on.
     
  2. Pommie

    Pommie Well-Known Member Most Helpful Member

    Joined:
    Mar 18, 2005
    Messages:
    10,162
    Likes:
    340
    Location:
    Brisbane Australia
    To get rid of the humming simply turn it off. If you want better suggestions give us more information.

    Mike.
     
  3. learning

    learning Member

    Joined:
    Dec 9, 2008
    Messages:
    179
    Likes:
    1
    Location:
    Kolkata,India
    I have attached some pictures for your information and other details as follows:

    Audio Amplifier: LA4440
    Transformer: 12-0-12 1 amp
    DC Filtration: Diode-IN5408(4 pieces); Capacitor: 4700uf/25v (2 pieces)
    Resistance: 5w / 150e
    Power Regulator: L7805CV
     

    Attached Files:

  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,592
    Likes:
    952
    Location:
    Canada, of course!

    Your messy tangle of wires probably feeds hum from the mains and transformer secondary wires and from the amplifier output to the amplifier input. Make the amplifier input wires shielded audio cables and separated from the AC wires and amplifier output wires after the wiring is made neat and tidy. The amplifier will produce hum if its input cables are not shielded audio cables.

    You might have a ground wire common to the high current parts and the low current parts then it causes a voltage drop of hum to the low current Bluetooth receiver. Separate the grounds as in a star and connect them together only at the main filter capacitor ground.
     
  6. learning

    learning Member

    Joined:
    Dec 9, 2008
    Messages:
    179
    Likes:
    1
    Location:
    Kolkata,India
    I could not understand what you say. Please elaborate it. Thank you!
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,592
    Likes:
    952
    Location:
    Canada, of course!
    The input ground, the output ground and the amplifier ground should all connect together only at the negative wire of the main power supply filter capacitor then there is no voltage drop of hum along a path. It is called a "star" ground.
     
  8. learning

    learning Member

    Joined:
    Dec 9, 2008
    Messages:
    179
    Likes:
    1
    Location:
    Kolkata,India
    Thank you for your explanation !
     
  9. learning

    learning Member

    Joined:
    Dec 9, 2008
    Messages:
    179
    Likes:
    1
    Location:
    Kolkata,India
    Humming is gone but sound from the amplifier is not coming. No sound from the amplifier. Please tell me the next action.
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,592
    Likes:
    952
    Location:
    Canada, of course!
    You probably have a wrong or missing connection in your messy tangle of wires.
     
  11. learning

    learning Member

    Joined:
    Dec 9, 2008
    Messages:
    179
    Likes:
    1
    Location:
    Kolkata,India
    Now I have attached new picture of the audio system and tell me where I have done wrong.
     

    Attached Files:

  12. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,592
    Likes:
    952
    Location:
    Canada, of course!
    Please post the wiring details of the Bluetooth receiver so that we can see the functions of its 6 wires. Your photo shows that its red wire does not connect to anything.
    Is the output of the LA4440 amplifier set for stereo or for one bridged output? Is it muted?
     
  13. learning

    learning Member

    Joined:
    Dec 9, 2008
    Messages:
    179
    Likes:
    1
    Location:
    Kolkata,India
    The red wire of Bluetooth amplifier is antenna wire. The output of the la4440 amplifier is for the stereo purpose. I have attached the latest detailed pictures for your requirement.
     

    Attached Files:

  14. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,592
    Likes:
    952
    Location:
    Canada, of course!
    I have never seen such poor soldering before. Don't you use 63% tin/37% lead name-brand rosin core solder?
    Photos do not show functions of the wires that the missing schematics will show. Please post the schematics.
     
  15. learning

    learning Member

    Joined:
    Dec 9, 2008
    Messages:
    179
    Likes:
    1
    Location:
    Kolkata,India
    I don't have any schematic.
     
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,592
    Likes:
    952
    Location:
    Canada, of course!
    A schematic is very important for any electronic circuit. You can make it by copying the manufacturer's schematic of the Bluetooth receiver, the power supply and the datasheet of the LA4440 amplifier. Then you will see the missing wire.
     
  17. JimB

    JimB Super Moderator Most Helpful Member

    Joined:
    Sep 11, 2004
    Messages:
    6,393
    Likes:
    593
    Location:
    Peterhead, Scotland
    Never mind the "missing wire", first fix the awful soldering and short circuits on the board.

    Look here:

    Bad soldering.png


    JimB
     
  18. learning

    learning Member

    Joined:
    Dec 9, 2008
    Messages:
    179
    Likes:
    1
    Location:
    Kolkata,India
    I have done it but still, the problem is staying. I don't know what I have to do. It is my bad luck.
     
  19. gary350

    gary350 Well-Known Member

    Joined:
    Dec 28, 2005
    Messages:
    1,103
    Likes:
    53
    Location:
    Murfreesboro, TN 37129 USA
    Bad power supply capacitor often causes AC Hum it is a very common problem.
     

Share This Page