Help with audioamp ?

Discussion in 'The Projects Forum' started by curry87, Aug 31, 2011.

  1. curry87

    Thread Starter Member

    May 30, 2010
    101
    0
    I have built this audio amp circuit the second opamp on the right is a lm386 not the tL072 that it says but am having the following problems with the circuit:


    1.Getting unwanted noise when the led sensitivity indicator lights.



    2.How can i modify the circuit to reduce other unwanted noises for example if i replace the 9v battery with a 9v wallwart ?



    3.How hard would it be to add a bass and treble control to this ?



    4.What else can i do to improve the circuit in general ?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,036
    You might consider the LM3914 to give even more LED levels while also simplifying the circuit overall. Do you have bypass caps on all ICs? That will help with noise. You'll want a voltage regulator if you want to use a wall-wart. If your wart is a regulated supply, for instance a 5V USB charger, that may work.
     
  3. JingleJoe

    Member

    Jul 23, 2011
    185
    10
    Filter caps accross the power supply (about 100uF cap connected between +V and 0V) really reduce noise when using an lm386, take note that it's not your ordinary op amp; it's a power amplifier for driving a speaker, it distorts quite nicely at high gain too.
     
  4. curry87

    Thread Starter Member

    May 30, 2010
    101
    0
    100uf and a 1nf cap across the power supply is that a good idea ?



    Do headphones normally have a 100ohm resistor in series with the decoupling cap on the lm386 output ?
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You saved your schematic as a fuzzy JPG file type instead of as a very clear PNG file type. The tiny writing on the schematic is impossible to see.

    The circuit powers the mic and the bias for the opamp directly from the +9V that jumps up and down when the LEDs light and turn off. The mic and bias should have their own filter.

    You forgot to describe the noise: High frequency hiss? Low frequency hum? Clicks when the LEDs turn on and off?

    Look in Google for Baxandall Tone Control. A good one uses one audio opamp.

    Headphones are normally fed through a 120 ohm resistor from a power amplifier so that loud sounds are not too loud.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,036
    I was able to zoom in and read it clearly. It's there, just far away.
    Picture 2.png
     
    Last edited: Sep 1, 2011
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I copied the fuzzy JPG file that has tiny writing and zoomed it to double its size. It was a fuzzy pastel so I increased its contrast. Now it is still fuzzy and it shows the JPG artifacts.
    I saved it as a PNG file so it doesn't have double the JPG fuzziness.

    EDIT. I clicked on the original attachment and it doubled its size clearly.
     
  8. curry87

    Thread Starter Member

    May 30, 2010
    101
    0
    Mainly low freq clicking when the leds change states.

    What filter would i need on the mic power and bias circuit lp or hp filter ?
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Here is the filter:
     
Loading...