For a project at my university, I am making a guitar effects switcher. Guitar effects work on instrument level audio signal which is AC only. I plan to use ADG2128 analog switch array (https://www.analog.com/media/en/technical-documentation/data-sheets/ADG2128.pdf) for this purpose. I am trying to achieve the following thing:
If I power ADG2128 from a single rail power supply (12V), I need to bias the input audio signal before routing it in the input of the chip, so it does not go in the negative voltage range, in order for the switch array to work.
I have never done something like this before, so my new question is how should the circuit for the DC biasing look like.
I need to add some DC voltage (DC bias) before sending the signal into the array and then remove this offset before sending it to the next effect. What is the proper approach to do this without accidentally filtering the sound or altering it?
Answer
The circuit below will provide DC bias for inputs to the switch, and remove DC bias on the outputs.
simulate this circuit – Schematic created using CircuitLab
"in" is any input to the switch. "out" is any output from the switch. The input bias circuit has a corner frequency below 1 Hz. It will pass frequencies above that. The output bias will have a corner frequency that depends on the input impedance of the next device, but will likely be 10k+ so should be ok.
Each input to the switch will need the input biasing below, whether it comes from a guitar, effects pedal, or other device. Each output from the switch will need the series capacitor to prevent the bias from getting to the next pedal, amp, or other device.
The capacitors should be ceramic type, which have no DC voltage polarity. X7R type ceramic has been suggested.
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