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After making a stereo circuit board with a TDA2030 and mobile aux as input, I wanted to connect an MP3/BT module to my own indigenous audio amplifier circuit which would make every action easier I supposed, but things went wrong.

In mono circuit, the Bluetooth does not output that highly annoying noise but I want it to be stereo.

Below are the pictures of my MP3 module:

enter image description here

enter image description here

The module has 5 modes which are:

  1. Bluetooth mode
  2. AUX mode.
  3. Pendrive Mode
  4. SDcard Mode
  5. FM Radio mode.

In Bluetooth mode, the noise is produced much more than others, unbearable Bluetooth spike frequency sound, in AUX and Pendrive mode, the noise is quite low (bearable.)

In FM Radio mode, there is almost no noise.

Here is my circuit:

schematic

simulate this circuit – Schematic created using CircuitLab

I also tried connecting some filters to the output of the MP3 module which were supposed to reduce noise.

Like this:

schematic

simulate this circuit

That did not work at all.

When I connect the stereo circuit input directly to my mobile stereo output using headphone jack, it works very well until I connect the module again.

Any suggestions or helps please? Please point me my errors using a proper schematic which will make it easier to understand for me.

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3 Answers 3

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You are basically shorting out TDA2030 inputs to ground in AC via C18/C19. You need to add another resistors between pin 1 of each channel (IN+) and half of power supply (R3/R4 and R11/R12). Audio signal goes into pin 1 like you do now from a capacitor.

Look closely at TDA2030 datasheet for single supply schematics.

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  • \$\begingroup\$ That is not the answer i asked, i shall fix what u said but I want it noise free which your answer didn't explain how to? \$\endgroup\$ Commented Feb 7, 2021 at 7:32
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    \$\begingroup\$ @SubhaJeetSikdar: Fix the capacitors first. They may very well be the cause of your noise problem. They reduce the audio level getting to your amplifier. \$\endgroup\$
    – JRE
    Commented Feb 7, 2021 at 9:15
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Some Bypass capacitors of 104 pf connecting to the power pins (+ve and ground) of the MP3 module solved this problem. Noise is quite low now.

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    \$\begingroup\$ Yes, these modules are notorious for bleed through of digital signals. In fact, you can truly hear the bluetooth connecting. \$\endgroup\$
    – P2000
    Commented Feb 16, 2021 at 6:00
  • \$\begingroup\$ Yes, some bypass capacitors connected to the power of the module solved the problem :) now the noise is low enough (bearable) \$\endgroup\$ Commented Feb 18, 2021 at 5:04
  • \$\begingroup\$ No such thing as 104 pF. Do you mean 100 nF? \$\endgroup\$
    – winny
    Commented May 26, 2021 at 8:09
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I did the modification and coupled to a mixer amp without any problems. There was a slight hissing from HF which I compensated by reducing the above 15 kHz audio range from graphic equalizer but can also be done by a 100 pF bypass filter across the input and also increasing lower frequency response by increasing value of C1 and C10 to 10 uF.

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