I’d like to build a simple box to switch the line output of my mic preamp to either a compressor, or an audio interface. Is there one switch that can do this? I assume it would need 9 contacts - three for the output, and three for each of the inputs. Beyond that, I don’t know what to look for.
Welcome to the forum.
Assuming a three wire common ground audio circuit, then a DPDT (double pole double throw) switch is what you need.
Signal commons of all three devices is tied together in the switchbox.
The mic pre-amp out positive and negative signal connections connect to the poles .
positive and negative signal connections of the inputs connect to the throws.
If these are XLR connections then the case grounds of all three devices should also be tied together in the switchbox.
To avoid clicks and pops when switching you can use a “make before break” style switch. (required for switching during a live performance)
Best to choose one with either silver or gold switch contacts for a low contact resistance (10 milliohm or less).
Here’s a style I’ve used a lot over the decades for switching audio circuits in a non-live applications (it’s break before make).
Thank you, Paul! I will need to study this, as the concepts are new to me. I also don’t understand why the connection being XLR would matter – wouldn’t the same apply if the connections into the box were TRS?
TRS has 3 conductors, and XLR is 4 conductors.
TRS uses the signal common for the shielding connection. XLR has separate signal common and chassis ground/earth connections to allow for better noise immunity. Not all devices with XLR connectors use that feature so, some devices will have the chassis ground/earth connection either left open or connected to signal common.
Thanks again for the clear explanation!
Yay! And the switch you pointed me to (pictured) is one that has the “silver contacts” you suggest?
Yes, it’s has good low resistance silver plated contacts.
That style switch is very versatile so I keep eight varieties in stock for my projects. I use them for switching audio, sensor signals, and power (up to 5A @ 120VAC/28VDC).