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I'm designing an audio equalizer with the option to relay switch between a solid state and transformer output path. I'm worried that the relay will cause an audible pop on the output as the relay switches. My thought is to use an additional relay that creates a resistive path to ground a moment before the output relay switches and remains active until the output switch becomes stable. I'm thinking for half second before and half second after. This needs to be accomplished with the Output Select DPDT switch. When the switch is activated the resistive shunt relay would need to activate half a second before the output relay switches and release half a second later. This process will occur each time the switch is pushed in or out. I will have 24 volts to activate the relays and the circuit. Does anyone have ideas

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    \$\begingroup\$ Why not an analog mux/demux? \$\endgroup\$ – Ignacio Vazquez-Abrams Mar 9 '14 at 23:53
  • \$\begingroup\$ @user38467 If you post a schematic or a block diagram of your proposed design, it will be easier to understand your question. \$\endgroup\$ – Nick Alexeev Mar 9 '14 at 23:56
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Anything that switches rapidly can cause a pop. Here's an example of a switch that is "popless" because it gradually changes the attenuation (courtesy of Vampire Squid Labs).

enter image description here

Some audio mux chips have a zero cross switching function built in which performs a similar function.

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  • \$\begingroup\$ So you would use one of these circuits for every input that needs to be switched, and tie them together at the node marked "To Amplifier" ? \$\endgroup\$ – tcrosley Mar 10 '14 at 19:05
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A relay in an audio path is going to cause a "pop" under two conditions:

  • If there's a voltage across it at the moment it closes.
  • If there's a current flowing through it at the moment it opens.

There's no way around this; if you can't avoid these conditions, then a relay may not be the correct solution for your application.

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