A muting delay & DC offset protection circuit


Posted on Feb 6, 2014

A low pass filter is merely a stable state-space system that has an input and spits out an output. If the input is a quasi-periodic signal, then the output would simply be the same quasi-periodic signal with a phase shift. Only difference would be that this system would have to transition from some initial condition (which would be ground, or the way you have it


A muting delay & DC offset protection circuit
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which is in disconnection mode). I see what you`re trying to accomplish. Phase shift the signal so that when we reconnect the headphones it occurs at zero-crossing time to avoid the small discontinuity in waveform. Good thought, but. If you`re trying to make a phase shift in a uniform way with respective to frequency then you need an all-pass filter, not a low-pass filter. But more to the point, you`ve got to remember that a relay is a mechanical device and it takes a small amount of time for the contact to close after energizing the coil. To do what you suggest here assumes that we know exactly when that is going to happen and, we don`t. And even if we did, transitioning from the phase-shifted version of the audio to the non-shifted version will still incur a small discontinuity in the waveform without doing something really fancy, and another relay is not going to cut it. And relay contacts do "bounce" when closing, how would that affect the signal Actually, no. Trust me. Do a little measurement on your own. Hook up your DMM in AC milliamps mode in series with the connected ground, play a test tone and watch your meter and you`ll get a reading of some amount of current. Now, disconnect the positive side of both outputs. Still got a reading Static discharge is tens of thousands of volts or higher, arcing across air. Headphone amp DC offset is much smaller and cannot do that. Have a look at the schematics of almost any...




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