LTSpice not looking like the actual measurement

Discussion in 'General Electronics Chat' started by Error3, Dec 27, 2012.

  1. Error3

    Thread Starter New Member

    Jan 10, 2012
    I have the hardware made for this chorus guitar pedal schematic:

    The pedal sounds perfect when I hook up my guitar through it, to my amp. During the making of this, I used LTSpice for each stage of the circuit. The first stage measured on the actual hardware looks very different than what LTSpice shows.

    I have images of the actual reading from the hardware. And I also included the LTSpice files as well (just change the TL082.txt to .301). I set both my function gen and my LTSpice original signal to 1V p-p at 440Hz.

    The LTSpice file signal references are:

    Green: Original signal out of V!
    Red: Signal after the cap
    Blue: Signal out the op amp

    The first photo is being measured after the cap, and the second photo is being measured at the output of the op amp on the hardware.

    Is this a problem that most people have using spice programs? Or can someone spot out something that I might doing wrong.

    Also for the Vb reference on the actual hard, I am measuring 5.3V.
  2. w2aew

    Active Member

    Jan 3, 2012
    A couple of things...

    In your simulation, you have the sinewave source set to 1V peak, which is 2Vpp. This is not the 1Vpp that you stated.

    The measured signal at the cap is showing more than 6Vpp. There should be no gain at this point, so I strongly suspect that you don't have the function generator amplitude set correctly. Depending on your FG, you may have to tell it what load impedance it is driving. If it is expecting 50 ohms and your are loading it with high impedance then the output will be larger than you set.

    The clipped 7Vpp output tends to confirm that your input signal is too big.
  3. Error3

    Thread Starter New Member

    Jan 10, 2012
    Yes sorry... both the signals on the FG and LT are set at 2vpp. I guess I am not sure what the load impedance would be, if I am trying to simulate a guitar signal.

    After doing another measurement (lowering the FG to 1Vpp from 2Vpp), it looks like the output of the op amp is matches the LTSpice schematic. However the measurement after the cap appears to been seen at a much high voltage than the actual reading, as seen in these updated photos.

    LTSpice was updated to 1Vpp btw.
    Last edited: Dec 27, 2012