speaker level output switcher circuit advice needed

Thread Starter

ryancousins

Joined Jul 15, 2012
14
I would like to remotely trigger a switch to change the routing of an audio amplifier's output to different speakers. I have a 2 channel amp, and by default, one channel powers the Left & Right speaker, and the other powers a subwoofer. I'd like the option to switch it so the Left and Right speakers are each powered by their own channel, and the sub gets disconnected. This would give me the choice between mono w/sub or stereo without. This is in an auditorium, with the amp rack up in a room a distance from the sound booth. (There is a DSP unit receiving the audio mixer's L,R,Sub outputs and I can write separate programs for it and change them remotely via an app or RS-232, so the changes I'd need to make on my input signal are all set.) I have extra unused line-level audio cables running between the two locations and I figured I could use one of them to send a small latching or control voltage down to change the state of the switch circuit from the sound booth. With my limited knowledge, I'm just thinking I'd need something like a DPDT latching relay (I'd rather not have to maintain a voltage full-time to keep it at a particular state. Am I in the right ballpark as far as methodology? Also, I'm wondering if I'd need to keep the negative of each speaker isolated? For most things you could probably tie the common together but I'm wondering if the amp is pushing out two separate differential signals without respect to a common reference? I've never seen speaker negatives tied together so I'm thinking I'd need a 4PDT relay? Is there a simple solid state way to handle this? These are very high power pro audio speakers so we're talking a decent amount of current. I've attached a diagram to illustrate.
 

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crutschow

Joined Mar 14, 2008
30,774
Yes, some amps have bridge outputs and thus you can't tie their commons together.
You can readily determine that by using a ohmmeter to see if there's continuity between any of of the speaker output pins with the power off.

Why do you not want to apply a continuous signal to keep it in one state?
If you do want a latching circuit, will you need some remote indication as to which state it's in?
 

Thread Starter

ryancousins

Joined Jul 15, 2012
14
I would only need to change states every once in a great while. So I'd just assume not have to maintain power to the switching circuit whenever the system is in use. However, that isn't a huge issue. If it made for a much simpler circuit, I'd be fine with having to power it the whole time. And yes, I suppose I'd want some feedback about which state the switch circuit is in.
 

crutschow

Joined Mar 14, 2008
30,774
I would only need to change states every once in a great while. So I'd just assume not have to maintain power to the switching circuit whenever the system is in use. However, that isn't a huge issue. If it made for a much simpler circuit, I'd be fine with having to power it the whole time. And yes, I suppose I'd want some feedback about which state the switch circuit is in.
Latching circuits generally do add to the complexity, especially if you want a remote indication.
And solid state switching would also be more complex.
The simplest is just to use a mechanical 4PDT relay and keep it energized for one state.
 
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AnalogKid

Joined Aug 1, 2013
10,125
If the amplifier outputs are BTL (bridge-tied load, no common terminal for all outputs), then you need 4PDT. If the outputs are standard analog power stages with a common (ground) potential for both speakers, then DPDT will work. Here is a DPDT mechanically latching relay.

ak
 

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