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Disturbing sound is coming from Bluetooth audio amplifier

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learning

Member
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.
 

Pommie

Well-Known Member
Most Helpful Member
To get rid of the humming simply turn it off. If you want better suggestions give us more information.

Mike.
 

learning

Member
To get rid of the humming simply turn it off. If you want better suggestions give us more information.

Mike.
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
 

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audioguru

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Most Helpful Member
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.
 

audioguru

Well-Known Member
Most Helpful Member
I could not understand what you say. Please elaborate it. Thank you!
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.
 

learning

Member
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.
Thank you for your explanation !
 

learning

Member
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.
Humming is gone but sound from the amplifier is not coming. No sound from the amplifier. Please tell me the next action.
 

audioguru

Well-Known Member
Most Helpful Member
You probably have a wrong or missing connection in your messy tangle of wires.
 

audioguru

Well-Known Member
Most Helpful Member
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?
 

learning

Member
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?
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.
 

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audioguru

Well-Known Member
Most Helpful Member
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.
 

learning

Member
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.
I don't have any schematic.
 

audioguru

Well-Known Member
Most Helpful Member
I don't have any schematic.
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.
 

JimB

Super Moderator
Most Helpful Member
Then you will see the missing wire.
Never mind the "missing wire", first fix the awful soldering and short circuits on the board.

Look here:

Bad soldering.png


JimB
 
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