Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How To Test Amplification

  1. Aug 23, 2009 #1
    Hi everyone, I been trying to modify a headphone amplifier that I have to make it better for my specific headphone response. The thing is that I am using multisim software to test before actually making the physical changes, the problem is that I don't know what tool to use to see if my circuit is actually amplifying or making any change. As the input I am using a function generator with 1khz and 10V of amplitude, but in the output I don't quite know if I need to use the oscilloscope, or any other specific tool to graph the changes. I did try to use the oscilloscope, in a schematic I found in a headphone forum, and I didn’t know what the amplification was, since I was giving a sine wave as input, and the output which came from an opamp was a square wave, so I got kind of confused. So that’s why I am asking.
    Thank you in advance for any help.
  2. jcsd
  3. Aug 23, 2009 #2
    Hello renegg.I would have thought that an oscilloscope is the best instrument to use for this.To get good amplification your output waveform should be similar to your input waveform but with larger amplitude.Since you are getting a square wave output it seems that your op amp is going to saturation i.e. acting like a switch rather than an amp.Perhaps you should try reducing your input voltage(10v seems enormous) and perhaps, your feedback ratio whilst the scope is connected to the output. Anyway,I am really rusty on this stuff and I know that there are electronics experts on this forum,hopefully someone will come in with better advice.
    Last edited: Aug 23, 2009
  4. Aug 23, 2009 #3


    User Avatar
    Science Advisor

    10 volts of input would overdrive most amplifiers. Try 100 mV or 0.1 Volts peak to peak.
    The output should look like a sinewave without any distortion and it should probably be bigger than the input, depending on the circuit.

    Actually, a headphone amplifier is partly about an impedance change so you can drive 8 ohm headphones when the rest of the circuit would be unable to drive them. So the actual voltage gain may not be all that much, but it should maintain a sinewave across a low impedance load like headphones.
    You should certainly use an Oscilloscope for this. That will tell you if you have distorted output or not.

    I have used that software and a predecessor of it and I found most of the time I was trying to keep the software happy and not achieving anything. It seemed extremely fussy about how you used it.

    Why don't you make the circuit for real and test it for real and then decide if you need to modify it? That is a lot more fun than playing with simulators.
    Put the circuit on here if you would like an opinion or two about it.
  5. Aug 23, 2009 #4
    Ok that was the problem I was giving to much voltage, with 10 volts I was seeing disorted waves as the output. With you're recomendations of .1 volts I can see know the amplification I am getting. And certailnly I will post the schematic here, since I don't have that much of experience designing and suggeestions and tips will be greatly appreciated. Thank you very much for you're responses.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook