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I would like to make a simple testing device that deliberately emits electromagnetic / electrostatic noise to test analog audio circuits for resistance to hum from switching power supplies, PWM outputs of microcontrollers, motors or whatever.

Can someone recommend a hum inducing circuit for testing analog circuits? Something like a loop of wire with a high voltage square wave perhaps? What would work best?

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  • \$\begingroup\$ If you're testing for interference from SMPS, why not just use a power extension cord and an actual SMPS and put it next to the case of your equipment? \$\endgroup\$ – us2012 Jul 3 '13 at 16:13
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    \$\begingroup\$ Hum is a word I associate with normal analogue supplies with transformers etc.. If you're going to test ana analoge circuit with hi-frequency interference from SMPSs it will usually be outside the audio range too so, to understand the question better what will your test measure/look for, and how will it measure it? \$\endgroup\$ – Andy aka Jul 3 '13 at 16:36
  • \$\begingroup\$ voltage hardly matters. go for current. fluorescent lights and heavily loaded switching power supplies could do the trick too. =P \$\endgroup\$ – JustJeff Jul 3 '13 at 17:44
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For electromagnetic/electrostatic noise, using a low voltage wall-wort power supply, voltage divide the power supply in half and attach the divided signal into a non-inverting op-amp. Use a 100kohm potentiometer connected to ground to adjust the amount of hum.

In general, the idea is to amplify the noise floor much higher than you would normally without any additional input. If you want SMPS noise, do the same with an SMPS power supply. The same goes for PWM outputs.

As a side note, white noise can be generated by doing the same thing with the stable output of a voltage reference IC as the input to the

For a really quick solution, use an MP3 player or computer with sample noise either recorded or found online. (This is most likely what I would do)

In the industry, a function generator tuned to the desired frequency or an arbitrary function generator with samples would be used.

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  • \$\begingroup\$ If you did use a function generator, how would you get the signal to effect the circuit as EM noise? A coil and a power amplifier? \$\endgroup\$ – Pete Kirkham Oct 4 '13 at 13:44

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