function generator - amplification (pc sound card through LM324)

Discussion in 'The Projects Forum' started by cyphergo, Nov 12, 2010.

  1. cyphergo

    Thread Starter New Member

    Nov 12, 2010
    Hi everybody,
    As the title suggests am trying to build a high power/current function generator. Am using a program called TTG as a function generator using my PC sound card, then I am trying to amplify the signal.

    I am using an LM324N, I was successful to amplify the voltage from ~0.01V (my sound card output) to about 1.1VAC (testing sine wave for now), however when I measure short circuit current of the output its a mere 40ma.

    Am i doing something wrong here? or do op-amps really give little current? and how should I go about amplifying the signal enough so it can drive... let's say a little ac motor.

    thanks in advance, and sorry for my noobness :)
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    OP AMPS have generally low output current.
    If u want more current try LM386.

    It can deliver around 2W. This shud be enuf to drive any circuit. The only problem is it will limited to around 20Khz as it is an audio amp, but since u said u will be generating signal using sound card, this is not much of an issue.

    But remember not to short circuit the output. Minimum load is defined in the data sheet, and so is how to construct the amp.
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    I think it is something wrong with your sound card setting. You should check your settings in control panel. Most sound card are able to output at least +/- 1 volt. So the output must be muted or you are using the wrong output, and what you see is cross over. Connect earplug and see if you can hear any sound or music. Then you know that you have the correct output. Most sound cards have a frequency range from 20 to 20KHz
    Also be very careful shorting any output from any circuit.
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    Further, if you need a substantial output, use an audio amplifier in place of the op amp.
  5. Wendy


    Mar 24, 2008
    Do you have access to an oscope? As I read your post you are trying for a function generator. A LM324 is a good little op amp, but it is old, very old, and slow. There are many better types out there, and almost all op amps have no drive to speak of. This can be corrected with more circuitry, but you need to see what your computer is doing first, which is why I mention the oscope.
  6. SgtWookie


    Jul 17, 2007
    Typical opamps might source/sink up to about 20mA before they start geting loaded down. As Bill mentioned, the LM324 is ancient and slow; its' gain-bandwidth product is only slightly better than a dying snails'.

    What you might do is use a more modern opamp for amplifying the sound cards' output signal, and then use a power opamp such as an L2722 as a voltage follower/buffer to provide more output current. The L2722 has a fairly low gain bandwidth product as well, but if you are using it as a voltage follower, it should be adequate - and it's quite inexpensive at around $0.70/ea.