Establishing 50 ohm soundcard output?

Discussion in 'General Electronics Chat' started by Mike33, Nov 13, 2013.

  1. Mike33

    Thread Starter AAC Fanatic!

    Feb 4, 2005

    Ok, got my first scope and am now setting up some some experiments!

    I am reading a lot about how to measure unknown inductors...consensus seems to be that if you use a function generator, you should have a 50 ohm output impedance by which the signal is fed to the scope. Altho it's not perfect, I plan to use a PC-based generator to get me in the ballpark on some measurements.

    How does one establish such an impedance? Run the soundcard output to a buffer? How to set the Z - just a series resistance? Or is there a trick using coax or something?

    Thanks, still learning!
  2. MrChips


    Oct 2, 2009
    Matching the coax cable impedance with correct termination resistors becomes more important as you go to higher frequencies.

    At the audio frequency range below 20kHz you should not be able to observe much difference.

    Don't worry about it.
  3. Mike33

    Thread Starter AAC Fanatic!

    Feb 4, 2005

    Thanks. I'd mostly be trying to find wah pedal inductors, L's to use for tone filters (audio effects) out of a box of unknowns. I'll give it a shot... :D
  4. t06afre

    AAC Fanatic!

    May 11, 2009
    I think it is some free software that use the sound card and PC as LCR meter. Some simple electronics will be needed also. But it is not hard to build the latter
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    If you check around on ebay etc you can buy a digital multimeter with inbuilt capacitance and inductance testing. Some even have a frequency meter.

    I have one that cost about $60 but they are even cheaper now.

    If you are going to be working with L and C (and freq?) for audio tone filters it would be a worthwhile investment, and you might get one as cheap as $30-$40 (but that's just a guess).
  6. Mike33

    Thread Starter AAC Fanatic!

    Feb 4, 2005
    Good point...but the better investment probably would be an actual frequency generator, given that they're not much more than the meter. After monkeying around with a PC-based one, I can totally see the problem with being limited to <21 kHz. Can't swing it high enough to do a lot of things.

    My DMM does C and F now, very well.