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Buzzing sound in speakers

Discussion in 'General Electronics Discussion' started by Karthik rajagopal, May 15, 2019.

  1. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    Hi guys,
    I wanted to created a simple stereo system . So I bought a audio amplifier circuit from the local market which works really great. The only problem is the continuous buzzing sound . The noise is considerably loud . It raises as I increase the volume . But disappears as soon as I touch the heat sink of the amplifier . So I soldered all the metal body of bass, treble , volume potentiometers and even the heat sink to the negative terminal. This reduced the problem to a small extent .
    I even tried soldering two 0.1micro farad capacitor with each channel (at audio input )with the negative of the audio jack but in vain .
    My a amplifier is based on 4440 ic and has two sets of the same circuit on a single board for two channels . I have attached the image below . IMG_20190516_002420.JPG IMG_20190516_002411.JPG
    I supplied it with 12v power from my bench power supply .
    Plz help me solve this .
     
  2. Audioguru

    Audioguru

    2,456
    542
    Sep 24, 2016
    Your wires are a mess all over the place. If the wires are much shorter and if some are shielded audio cables then they will not pickup mains hum interference.
     
    Karthik rajagopal and Bluejets like this.
  3. Bluejets

    Bluejets

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    652
    Oct 5, 2014
    Commonly known as a rats nest for good reason.
    I'm guessing the small perforated board adjacent with the unshielded wires is the inputs.
     
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  4. FuZZ1L0G1C

    FuZZ1L0G1C

    347
    106
    Mar 25, 2014
    K.R, as you mention buzzing, I guess it's near radiating source such as fluorescent lights, TV screen, computer, etc.
    In that case, then as AG suggested in #2, keep leads short, screened.
    In addition, you should mount the amp in a grounded metal enclosure.

    Are you testing with one input source, such as your computer line-out / speaker out?
    It could be that the source itself is also noisy.

    I had a similar irritating buzz several years ago when digitizing a pile of old audio cassette tapes to hard disk via a USB tape player designed for this purpose.
    I ended up paralleling a 1μ audio-grade cap across the tape motor, as it had none to start with.

    If saving noisy recorded audio files to disk / flash memory, for future use, you can use Audacity or similar to remove most of the buzz by two methods I have used:

    1. 'Noise Reduction' function, which may sometimes create strange boops and beeps at certain harmonics.
    2. Record sound/music, then record only buzz, import both on separate tracks, invert noise and mix to cancel out noise.

    I used method 2 along with suppressed tape-motor with good results.

    FzLgc.
     
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  5. Audioguru

    Audioguru

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    Sep 24, 2016
    Most of your "wires all over the place" are antennas that pickup the electricity 50Hz or 60Hz all around you. Shielded (some people call it screened) audio cable blocks interference. Shorter wires reduce interference.
     
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  6. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    Thanks for the reply . I am using a one input source from my mobile phone's head phone Jack. "grounded enclosure " does that mean I must keep it in a metal enclosure which is connected to the negative terminal of the power supply ?
     
  7. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    Thanks for the reply .I actually needed that length for me to mount it in the closure . If I have to shorten ,what would be the minimum size ?
     
  8. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    Thanks for the reply . Yes, the small perforated board is the audio input Jack. I don't know how to shield those wires. Will twisting them over each other solve my problem?
     
  9. davenn

    davenn Moderator

    13,147
    1,706
    Sep 5, 2009

    Use shielded ( screened) lead it's readily available
     
  10. Audioguru

    Audioguru

    2,456
    542
    Sep 24, 2016
    Shielded audio cables are purchased, not made. Almost every audio equipment store sells them and almost all audio equipment comes with them. You can buy an entire roll of shielded audio cable to make the lengths you need.

    The input cable between your phone and the amplifier's input must be a shielded audio cable.
    The output wire from the bass control, treble control and volume control should use a shielded audio cable.
     
  11. Audioguru

    Audioguru

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    542
    Sep 24, 2016
    There is an "other side of the world" problem.
    He buys a Salcon amplifier in a market in India but we buy it from a local audio store where they also have shielded audio cables.
    He has never seen a shielded audio cable or other things that are common here.
     
  12. Bluejets

    Bluejets

    3,303
    652
    Oct 5, 2014
    Looks like this ...........
    Shield is normally attached to ground (frame....negative ) at the amp end and not the other
     

    Attached Files:

  13. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    It already has a shielded core cable for volume control and for the audio input. The unshielded wires are those soldered by me as an extension . I did not know that the small piece of unshielded wire can act as an antenna and pick up all the noise . If so I will remove that, solder it with the shielded cable.
    I thought of using a twisted pair cable as it can reduce the noise interference to decent level .
     
    Last edited: May 16, 2019
  14. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    The shielded cable included with my PCB has two wires connected to the circuit and one silver braid connected to the negative terminal. I Will change those and will also try keeping it in a metal enclosure connected to negative terminal so as to keep the annoying noise out.
     
  15. Audioguru

    Audioguru

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    542
    Sep 24, 2016
    When you extended the original shielded audio cables with your ordinary wires, you should have asked yourself, "Why did they use shielded cables instead of ordinary wires?". Twisted wires are used for telephone lines that are completely balanced (signals are on both wires and a wire is not grounded) and telephone wires do not carry low or high audio frequencies.

    I have many audio amplifiers and circuits on small circuit boards using shielded audio cables for inputs and controls. They are installed in plastic boxes (not metal) and they play no interference noises.
     
  16. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    I thought that small piece of wire won't pick up any noise. After reading your above message , I am clearly able to understand the significance of shielded core cables . Thanks for the help!
     
  17. BobK

    BobK

    7,542
    1,613
    Jan 5, 2010
    In my experience, line level signals are not that subject to picking up hum. When testing the speakers I built recently, I connected my phone output to line inputs without non-shielded wires about 10 inches long and there was zero hum.

    Is it possible you are using a low level (microphone) input instead of a line input? Is you phone volume turned very low when you connect it?

    Bob
     
  18. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    I use the input from the audio jack on my mobile phone and connect it to the amplifier. I usually turn the volume in my phone down(will be set to 30%) as my amplifier amplifies it to a great extent . Anything above 70% will make the music jarring , my speakers won't be able to handle that.
     
  19. BobK

    BobK

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    1,613
    Jan 5, 2010
    Are there multiple inputs to the amplifier, if so, how are they labelled, and which one are you using?

    Bob
     
  20. Karthik rajagopal

    Karthik rajagopal

    174
    4
    May 9, 2016
    I am just using an audio cable whose left and right channels are connected to the left and right sides of the amplifier respectively and the ground pin is connected to negative . I am not using multiple inputs .
     
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