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I have designed this audio multiplexer

enter image description here

This is a 4 input TRRS audio switcher. Remember TRRS (4 pins: mic, left, right and ground).

I press a button and I change the input that I want to send to the output.

This switch is supposedly to work as a "universal" switch for all kinds of inputs and outputs.

Unless I connect the output of this circuit to a pre-amp, the output will always be a headphone.

But this is my problem:

Apple earbuds are 23 ohms, Audio-Technica ATH-M50 is 38 ohms, Sony MDR7506 studio headphone is 63 ohms and more pro headphones have higher impedances.

How do I deal with this?

Suppose this switcher were created with a rotary mechanical switch. Then, the input that I select would be directed to the output. So the impedance of the device at the input of my circuit would be "passed" to the output. End of story.

But this is digital. Is the behavior the same? Should I do something or let this the way I have designed and simply add a pre-amp before the output to amplify any signal that is too low?

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Apple earbuds are 23 ohms, Audio-Technica ATH-M50 is 38 ohms, Sony MDR7506 studio headphone is 63 ohms and more pro headphones have higher impedances.

How do I deal with this?

I'd add a small stereo power amplifier at the output just prior to the headphone socket like you mentioned. You don't really want to be passing HiFi currents through an analogue switch like this because of non-linearities in the channel.

Or just swap-out the part for a type with much lower impedance and see if it sounds OK. The MAX309 is functionally compatible and has impedances about one-tenth of the part you are using for instance. However, if you do go down this route you will need to think about making your capacitor signal couplers bigger in value.

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If you get good enough analog switch parts with low ON impedance then this should work OK but you will want that ON impedance to be down in the low Ohms of resistance.

Also make sure to check the specs for the switches at the +5 and -5 rails you intend to use. The impedance can vary for parts that have a range of working supply rails.

Lastly your schematic shows no source voltage to supply the -5V input regulator (the 7905). You will need that for the circuit to work.

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