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    Noise in My Audio Amplifier

    Hi there
    I have a situation here regard to the audio amplifier noise.
    This is the audio source circuit (CODEC) :
    Click image for larger version. 

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    This is the audio amplifier circuit :
    Click image for larger version. 

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    And here it is the audio amplifier PCB layout :
    Click image for larger version. 

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    There are some facts :
    1 - With no input to the amp there is no noise at speakers output at all.
    1 - When I Connect my audio source to my amp there is a lot of noise which change with cable movement or touching components in the circuit.
    2 - When I connect a different audio source (rather than my source from picture 1) for example from computer output to the amplifier there is no noise (very low noise).
    3 - When I connect my audio source to a different amplifier (for example my computer speaker) there is no noise at all.
    4 - When my audio source (CODEC) is off there is noise but when I put a 1K resistor at the amp's inputs , noise will be disappeared. But when CODEC is on the resistor has no effect on the noise.

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    Re: Noise in My Audio Amplifier

    Hi,

    I can't see where you joined both Grounds.
    If you you did not yet connect them, then connect them.

    Else:
    I assume you created a ground loop. Show the complete cabling including power supplies.

    Klaus
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    Re: Noise in My Audio Amplifier

    Thank you Klaus.
    I hope my sketch be good enough :
    Click image for larger version. 

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    - - - Updated - - -

    I'm sorry. This is more detail of amp circuit that I forgot :
    Click image for larger version. 

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    I've shorten all jumpers for GND.



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    Re: Noise in My Audio Amplifier

    Hi,
    here a snippet, there a snippet...this even confuses yourself.
    Do it for yourself: draw a sketch with all your GND connections and you will see the loop.

    Additionally you did not follow the PCB layout recommendations in the datasheet about star GND.

    Follow the recommendations....

    Klaus
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    Re: Noise in My Audio Amplifier

    It is not clear whether you have made experiments with the JMP2 connected or not. Another point worth mentioning is that according to the first schematic, you are apparently performing a speaker feedback path for the signal ground through the 100K resistors whereas it would be expected to be done to the chassis ground, instead (or rather, is it really necessary?). In addition, the microphone's reference track bellow J4 does not help much to equalize this potential among each device, it seems like floating, not connected to anything else; think of drawing a plane there connected to all devices referenced by signal ground. BTW, is the MIC cable shielded ?
    --------------------------------------------------------------------------------------------------
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    Re: Noise in My Audio Amplifier

    Please describe the noise: Low frequency hum? High frequency hiss? A continuous tone? A pulsing tone?



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    Re: Noise in My Audio Amplifier

    Quote Originally Posted by KlausST View Post
    Hi,
    here a snippet, there a snippet...this even confuses yourself.
    Do it for yourself: draw a sketch with all your GND connections and you will see the loop.

    Additionally you did not follow the PCB layout recommendations in the datasheet about star GND.

    Follow the recommendations....

    Klaus
    Please read my first post as I mentioned my amp and my source work fine separately . The problem is they can't match with each other.



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    Re: Noise in My Audio Amplifier

    Quote Originally Posted by andre_teprom View Post
    It is not clear whether you have made experiments with the JMP2 connected or not. Another point worth mentioning is that according to the first schematic, you are apparently performing a speaker feedback path for the signal ground through the 100K resistors whereas it would be expected to be done to the chassis ground, instead (or rather, is it really necessary?). In addition, the microphone's reference track bellow J4 does not help much to equalize this potential among each device, it seems like floating, not connected to anything else; think of drawing a plane there connected to all devices referenced by signal ground. BTW, is the MIC cable shielded ?
    There are 2 RCA connectors : one is located in CODEC board and one in the amp. Each one of these connectors have a jumper . I put these jumper to prevent ground loop . At first I connect only one in the CODEC board and there was noise. Then I connect amp jumper too and still was noise. So right now 2 jumpers are connected. BTW there is no MIC and I'm sorry made you confused.
    Most confusing part is CODEC board and amp board work fine separately but can't work with each other.



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    Re: Noise in My Audio Amplifier

    Quote Originally Posted by Audioguru View Post
    Please describe the noise: Low frequency hum? High frequency hiss? A continuous tone? A pulsing tone?
    There are some random voices that change with these actions :
    1 - micro controller and other processing units cause noise. I mean for example when a certain data transfer happen between digital circuits you can hear it in the speaker.
    2 - when I move RCA cable around there is some changes in noise sound.
    3 - with reducing the length of the cable I realized there is a little reduction in noise level.



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    Re: Noise in My Audio Amplifier

    Hi,

    Please read my first post as I mentioned my amp and my source work fine separately . The problem is they can't match with each other.
    No.
    There are several issues.
    And one is, that when you connect all ... then you generate the ground loop.

    Klaus
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    Re: Noise in My Audio Amplifier

    Quote Originally Posted by neekoo View Post
    So right now 2 jumpers are connected.
    At the above schematic there is only 1 jumper shared among 2 connectors (presumably within the PCB board), namely JMP2, whereas you said above that there are 2 jumpers, so perhaps we`re not talking about the same thing. I have to admit that I am not understanding the general scheme of connections, so it would be advisable to as much as possible draw everything in a single diagram instead of describing it verbose or incrementally adding snapshotings, in order to avoid further misunderstandings.

    Quote Originally Posted by KlausST View Post
    draw a sketch with all your GND connections and you will see the loop.
    This will not only help you, but also others to better have a clear picture of the overall connection.
    Whenever dealing with low level analog signals, grounding scheme matters, a lot.
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  12. #12
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    Re: Noise in My Audio Amplifier

    JMP1 seems to connect SGND and PGND near J4.



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