I have a function generator that will emit an audio tone. I have two coils of wire and I'm trying to couple the audio signal from the primary coil to the secondary coil. The output of the secondary coil will be fed to an audio amplifier I bought from jaycar ( https://www.jaycar.com.au/low-cost-mains-powered-stereo-amplifier/p/AA0472 )which I would hear the tone with some headphones. A circuit of what I'm trying to build is shown below with labels and the inductance values of the coils. enter image description here

A few things I'm unsure about my design. Will this setup damage my function generator? Should I account for impedance matching? Should I have the two parts of the circuit connected to a common ground?


1 Answer 1


Will this setup damage my function generator?

If you have a commercial function generator, it's very likely to have a defined output impedance, usually 50ohm, 120ohm or 600ohm depending on the intended use, and be safe into a short circuit. Check the manual, just to make sure. If you have built one yourself, then only you will know.

Should I account for impedance matching?

There is no impedance matching in what you've shown, so nothing to account for. If you want to start getting quantative about what you measure, then the magnetic field produced by the first coil is proportional to the current flowing in it, and the voltage produced by the second is proportional to the rate of change of field in the first. Measure those.

Should I have the two parts of the circuit connected to a common ground?

As the intended signal coupling is entirely by magnetic field, it doesn't matter. Note that if both your amplifier and function generator plug into mains, you may well have, through the chassis and safety earth. If you connect a second 'earth' connection between them, you may well introduce picked up noise into the amplifier through an unintended loop.

  • \$\begingroup\$ My function generator has an output impedance of 50ohms. What else should I be checking for in order to not damage it? \$\endgroup\$
    – Guy Lee
    Apr 26, 2017 at 11:35
  • \$\begingroup\$ If it's a 50 ohm output impedance, it will be fine to drive any load, down to a short circuit. What else should you do not to damage it? Don't throw it off the top of a building, don't fill it with epoxy resin, don't plug it in directly to overhead 275kV power lines, the usual sorts of precautions. \$\endgroup\$
    – Neil_UK
    Apr 26, 2017 at 11:43

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