What component to use for audio signal switching?

Question

I'm looking to build a guitar pedal switcher based on a Raspberry Pi or Arduino (have not yet decided, but I have an unused Raspberry around and I lean towards that). Anyway, digital logic.

Now, I need to switch audio signal obviously and I need to do it quietly (both physical silence and electrical silence). Please note that the signal is line level throughout most of the build, except for the input which is much lower. I will probably have 2 or 3 loops before the preamp so those may not encounter line level signal.

From what I read and know, so far, mechanical relays are not really an option due to the clicking noise they make. I also read something about FETs, but that's a bit out of my league and I would appreciate any info on these.

PS: I will probably use different power rails for the digital and analog paths.

PS2: The whole thing will be mounted in a 1U rack enclosure, so please tell me if I should take into consideration any thermal issues.

Answer 1

I'd consider using analogue switches to do this - they are used extensively on switching thermocouples in and out of circuits and thermocouples are very low level signals. For example, the DG409 is used in this type of application and is specified in the brochure for audio routing applications. They are low power devices too. They can operate with a single +5V supply or from +/-5V supplies to +/-20V. The DG409 has two 4:1 multiplexers meaning you can route your signal to one of four places or choose on of 4 signals to route to a single place. This type of analogue switch comes with different switch configurations such as changeover or normally open too.

Answer 2

Have look at the 4066 analogue switching IC. There's a low-distortion version MAX4066 made by Maxim.

Answer 3

As Andy aka suggests, the DG series of ICs is an industry standard solution. There are various configurations available, four switches per package, with active high or low or a combination of these.

If you want to drive this with a mechanical switch, you want a robust momentary action which does not make physical noise. If there is no microcontroller, you can use something like a 555 bistable circuit to flip the switch state on each switch press. This is a nice solution for replacing "stomp boxes" which typically have an acoustically noisy DPCO footswitch - OK for a loud stage environment but not great for, say, a musician working a theatre pit when the stage should be quiet. (At risk of unintended self-promotion, I used this technique successfully on my MASSCOT guitar pedal, which is being used by some pro guitar players in my area.)