Project involving Op-amp, microphone, and speaker

Discussion in 'The Projects Forum' started by jimmyho08, Oct 7, 2013.

  1. jimmyho08

    Thread Starter New Member

    Oct 7, 2013
    16
    0
    Hi, I am building a project where I am using an op amp to drive a very small audio signal from a microphone. The problem was that just using the audio signal from the microphone was not enough to produce an audio signal at the speaker. Therefore, I created an op amp to make the sound better at the speaker side. Well, right now when I have the speakers hooked up to the op amp, and I've disconnected the microphone, the speakers are making a rattling noise/static noise. I am wondering why that is? The speakers are idol, it is making that the noise. Any ideas?

    Any help is appreciated.
     
  2. paulktreg

    Distinguished Member

    Jun 2, 2008
    611
    120
    Can you post a schematic?
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,137
    3,054
    A schematic - showing the identification of the op-amp - would help. You may be listening to noise, power supply noise, who knows.
     
  4. jimmyho08

    Thread Starter New Member

    Oct 7, 2013
    16
    0
    Sorry about that. Here is the op amp schematic, and my power supply circuit. The input power is coming from a AC-DC plug into the outlet power supply that produces 12V dc.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,137
    3,054
    Thanks for the details. This is a great example of why we ask for schematics. That is not an op-amp, it's an audio amplifier. That's actually good for your application, but it has different needs than an op-amp.
     
  6. #12

    Expert

    Nov 30, 2010
    16,306
    6,815
    Try adding 10 uf from pin 7 to ground and see if that clears anything up, change R3 to a potentiometer, about 10K so you have some gain control, and check for loose connections. Then show us the microphone circuit and exactly what kind of microphone it is.
     
  7. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Does the static noise change as you rotate the 1k pot from off to fully on?
     
  8. jimmyho08

    Thread Starter New Member

    Oct 7, 2013
    16
    0
    Ok, I will try to add the capacitor at pin 7, and try to add a pot to change the gain.

    The static noise does change when I rotate the 1k pot. That is to control the volume. Fully on causes the static to be heard louder than when the pot is closer to being off.
     
  9. #12

    Expert

    Nov 30, 2010
    16,306
    6,815
    That's why it is important to show us the microphone circuit.
     
  10. jimmyho08

    Thread Starter New Member

    Oct 7, 2013
    16
    0
    I unfortunatley do not have the mic circuit. The mic circuit I believe has nothing to do with the noise. I want to try and explain where the audio source is coming from.

    There is a IP Camera which can communicate two ways if a speaker and mic is connected to the appropriate wires coming out of the camera. You can have two communication between a laptop with a mic on it, and the person by the camera can hear them with the speaker connected to the camera. The 3.5mm jack where the speakers connects on the camera side, while idle, has terrible noise, which is what I hear on the speakers.

    I have tried to use a high pass filter, and low pass filter to try and smooth out the noise, but all I've managed to do is just lower the sound as the static becomes less and less.

    Any other suggestions? My next thing to try is to change the gain of the circuit while having the high pass and low pass filter and see if that works.
     
Loading...