Audio Amplifier Project

Discussion in 'The Projects Forum' started by ElecEngg, Mar 10, 2007.

  1. ElecEngg

    Thread Starter New Member

    Mar 10, 2007

    I have to design an audio amplifier for my project but first need to build a bandpass filter..I just wanted to know..should i put the output of the bandpass filter as the inputs to the op-amp..
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    There just about has to be more than one op amp involved, so a schematic would really help for us to try to answer your question.

    Just as a note, an audio amp usually has the filtering built into the feedback loop.
  3. ElecEngg

    Thread Starter New Member

    Mar 10, 2007
    0 far i have just come up wid te bandpass filter with resitors n capacitors and cant seem to simulate it in pspice. I mean am using the required 15V as my voltage source but i think am not using the right settings..Is there anyway that i could put up my schematic so far for you guys to have a look?
  4. hgmjr

    Retired Moderator

    Jan 28, 2005
    If you can save the file as a BMP, JPEG, or PDF file you can post it here.

    If you can't save it as one of these file types, then you can zoom the view of the schematic so that it fits your monitor screen and then press and hold the ALT-key down while you press the printscreen key. That will save the screen to the clip-board. You can then open up a Word Document and click on paste into the document.

    You can then post it as a .DOC file.

  5. ElecEngg

    Thread Starter New Member

    Mar 10, 2007
    Well ere's my doc file uptil te first part of the circuit,i've built a bandpass filter which supposedly should filter out frequencies between 400Hz-18KHz and in the second part..i have put the output into the op-amp which should have a gain of not sure i've got it right though..
  6. rwmoekoe

    Active Member

    Mar 1, 2007
    Hi ElecEngg..

    i've looked at your schematic.
    1. the supply voltage should be: +vcc (in this case 15v) should be the pos (+) lead of the battery, and connected to pin 7 of the opamp, while the min (-) lead of the battery should go to the gnd.

    2. there should be a neg supply for the opamp to work properly: -vee (in this case -15v) and it should be the min (-) lead of another battery, and connected to pin 4 of the opamp, while th pos (+) lead of this battery should go to the gnd.

    3. the values of the resistors are too low. the proportions will do, but convert them higher. say 10 to 100 times in values. the caps will have to be converted down by the same factor.

    4. the configuration of the input stage filters should be changed completely.

    5. use stage 1 as high pass: from input, series the input lead with a 39nF cap, then 10k res to the gnd to form a 400Hz high pass filter. the junction will go to the second stage, the low pass filter.

    6. use stage 2 as low pass: from the 1st stage, connect a 47k res, then a 180pF cap to the gnd to form an 18kHz low pass filter. the junction will go to the non-inverting input of the opamp.

    7. remember the formula of voltage gain for an opamp, in this case g=r3/r4+1. this will give your circuit a 19.3 gain in the bandwidth. (in case the gain factor is important to your purpose, otherwise it's ok)

    good luck!