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I've wired an external piezo as contact mic to the TRRS 3.5 jack of an iMac and it is working fine - BUT the signal will just randomly stop after hitting the contact mic several times too hard, so I suspect the iMac kills the connection after it gets too high voltage spikes from the mic...?

How can I avoid/dampen these signal spikes?

This is the way it's wired (needs to have that 10k in parallel for the mac to recognise it as a mic and the 33ohms are there to fake the speakers on L/R channels)

enter image description here

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I think I just found a solution - it's rather hacky I guess, but it suits my needs. Using two LEDs as a limiter to avoid voltage spikes. I took the idea from here: http://www.zachpoff.com/diy-resources/simple-contact-mike

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Here is an interesting article on protecting digital inputs using resistors, zener diodes and capacitors.

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  • \$\begingroup\$ This doesn't actually answer the question. Your link deals with protecting digital inputs, while this question deals with preventing an audio input from changing modes. \$\endgroup\$ – JRE Aug 4 '15 at 10:30

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