Question about relays

I’m new to the Audacity Forums, so please let me know if there is a better place for this sort of question.

I’m renovating a room, and currently, I’m researching volume control components. Aside from general volume control, there are two amps that I would like to switch between: one controlling a local microphone, and one for a music player. I’m thinking about getting a basic volume control knob and then adding in a relay for switching the source.

From what I’ve read, it seems like a 2-pole/1-throw relay should be able to do what I need. However, when I scan through a site such as, there are quite a few different options for 2P1T relays.

Does anyone have suggestions on what to look for when purchasing this sort of relay? Are there any reputable brands/models that I could use as a reference?


I would use a single pole switch (keep ground connected and switch only the signal wire).
Ensure that the switch comes before the volume control so that you can turn the volume down before switching (otherwise the switch may cause a click that could be very loud).

General advice - keep any unshielded signal wires short, and if possible place the electronics in a grounded metal box to shield from hum.

The brand name of the switch is unimportant. Almost any switch will do.

I assume you are going to build some sort of control box. If you are going to use relays, you are goingto need switches to switch them and power to power them. The switch steve suggests would do it, but we need a circuit diagram to see exactly what you are intending…??
The links below show cheap but good quality Audio/Video switch box for the type of application you have…

These are already built and designed for the job…??

Digi-Key is a reliable supplier. They sell products from “known” reliable manufacturers and they provide manufacturer part numbers and links to the datasheets, etc.

I assume these are line-level signals… Line-level audio is low-voltage & low current so any relay will do. Choose one that looks easy to wire-up or one that fits mechanically, etc.

Don’t power the coil with AC because you might get hum.

Unconnected inputs & outputs can sometimes “float-up” (DC voltage) and that will create a pop when connected. A ~10K resistor to ground on the inputs & outputs will prevent that.

They are all 70V distributed speakers.

After additional thought, I’m leaning toward getting a DPST switch rather than a relay/switch combo.

Is there any benefit to using both a relay and a switch in this situation? Should I worry about adding noise to the output by directly splicing in a switch?

Digital switching would be better, as it allows switching to be virtually instantaneous with zero bounce, but assuming that you turn down the volume before switching it really does not matter.


Please post a diagram of your system, it would then be easier to provide help.
I assume you have an distribution amplifier with 70 volt line output to either 70 volt speakers of via transformers to 4 or 8 ohm speakers.
Does your amplifier have mono inputs for a microphone for probably paging, and a Aux-in or Line-in for probably background music. Does it have basic volume and tone controls and do you currently route audio to the distribution amplifier with standard audio patch leads plugged in.
And you want to upgrade the changing of patch leads to a switched system.
OR has your amplifier just got one input mono.

Edit… I have just noticed you say… " there are two amps that I would like to switch between"… does that mean two 70 volt systems one for Mic and one for Music and do you want to end up with one 70 volt system doing all. …?>

Here is a diagram of the whole setup. It is a double room split by an air wall.

For this post, I had only been focusing on switching between the amp and the music player.

However, I’m also pondering ways to switch the mic output between operating separately (each mic only controlling its half of the room) and combined (both mics controlling all four speakers). I’m currently thinking about adding a wire between the mic inputs on the two volume controls and splicing in an SPST switch.


*note: I just realized that I drew the speakers running in parallel. The two pairs of speakers are daisy-chained.

I am confused on what is connected to what. And the locations. Have you one 70 volt amp with several inputs and the music player all in one location. Then long 70 volt lines out to room volume control and speakers.

I probably should have drawn the Mic Amps near the actual Mics with lineout back to main 70V Amp input.

When choosing a 2P1T relay for volume control, consider factors like contact rating, coil voltage, switching speed, contact configuration, mounting type, reliability (brands like Omron, Panasonic), and size. Verify that specifications meet your needs, and consult datasheets for detailed information. Reputable brands ensure reliable performance in your audio switching application.

Thanks for the help! I ended up using 2P2T switches to change between mic and music. So far, so good.

Out of curiosity, what program do you use for making diagrams?

Good that you got it going and we provided some help.
The program I used for the drawing (not a drawing program at all … blue line and grey background ) is the simulation program LTspice actually for drawing and simulating electrical and electronic circuits. All I did here was draw a few boxes and connect them up with wires and take a screen dump… google LTspice you will get lots of hits to find out more