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Passive speaker switcher
Old 3rd March 2014
  #1
Gear Nut
 
🎧 5 years
Passive speaker switcher

Hey guys

Did a fair bit of trawling on google before I decided to make a new thread here. simple idea. I have 3 sets of speakers in my room. Monitors, hifi and PA

I want to make a box with 3 switches on it that takes the output from my interface (motu 828 mk3) and can connect/disconnect any of the pairs of speakers, for referencing purposes.

My original idea was to use a 4 pole single throw switch for each set of speakers, so hot/cold from each XLR from my interface connect to 1/2/3/4 and connect directly to XLR outputs. The hifi amp is unbalanced input so of course tying cold to ground on this output. I planned to connect all ground wires.

Then I started thinking about clicks/pops upon connection and have come across conflicting info on whether I want make-before-break or vice versa switches to avoid this. I wonder if it can be so easy considering my 828 still makes a pop if my monitors are on when it powers up.

I'm still rather noobish with electronics so any help would be appreciated. It seems like this should be DIYable. To be clear, this would of course be line level, coming before the hifi amp, active monitor amps and active pa amps. From my experience making basic cables and adapters as long as all the soldering is solid and the connectors are good quality the audio quality should be fine?

While I would never be running 2 sets of speakers at once, is there any cause for concern with this happening briefly while hitting 2 switches at once to alternate speakers?

Lastly if there is any easy schematic floating around for this I would be much appreciative
Old 3rd March 2014
  #2
Lives for gear
 
🎧 15 years
Hi
This kind of project has been done, discussed and beaten to death so many times on GS.
Cheap and cheerful 'simple' switching 'works' but has some drawbacks with possible 'clicks' and crosstalk / noise if amplifier inputs are left 'disconnected'.
Please read and learn.
Matt S
Old 4th March 2014
  #3
Gear Nut
 
🎧 5 years
Apologies... I did a bit of a search and could mostly only find information on switches after the amplifier stage.

All for reading and learning... I do that a lot. I find that I learn more if I am able to ask questions specific to my situation & knowledge level.

Maybe easiest to just not respond if you don't have anything useful to say to me - I did state right in the opening sentence that I had already been looking. Gearslutz is a primary source of such info for me, it goes without saying.

What makes clicks "possible" and how can this be ironed out?
Old 4th March 2014
  #4
Lives for gear
 
Lotus 7's Avatar
The "passive" speaker switch (in your thread subject line) is actually one to switch "active" monitors or in your case the active, line level inputs to your amplifiers. These are typically called "active monitor switches", not because the switch is "active" , but because the devices being switched are active. Generally a "passive speaker switch" refers to a switch used to switch the high-current speaker lines between amplifier outputs.

As Matt said, there have been many posts on this subject. I've in fact posted schematics of several XLR/XLR switches on this forum.

For your application, a simple solution is to use a low-cost Hosa SLW-333 switch. It's a rotary switch (so only one output can be selected at a time). The Hosa has fully balanced TRS inputs and outputs. You would connect your interface outputs to the switch with a balanced XLR to TRS cable. Then connect the outputs from the switch to the respective amp or active monitor inputs with the appropriate cables.

For instance, for active monitors with balanced inputs use TRS to TRS or TRS to XLR balanced cables depending on what your active monitors use for input connectors.

For a "hi-fi" amplifier input on RCA jacks, use TS to RCA (unbalanced) cables

For your "PA" system use whatever matches the inputs.

If you don't like using a rotary switch, the Coleman LS3 push button switch will provide the exact same functions. I prefer the Hosa since it's built into a rugged metal box and costs less then the Coleman, but either one will do the job. Both of these switches are fully passive, that is they can be used to switch one pair of outputs to (3) different inputs, OR they can be used to switch (3) different inputs to one output. The Coleman PB switches are independent, so you can select one, two, or all three outputs at the same time. I don't consider that an advantage, but you might.

Re: "clicks": If you have any DC offset on your outputs, any DC build up on an input due to an unterminated input coupling cap, or if you switch while an audio signal is being sent through the switch, you will probably hear a "click". Normally this is not an issue, especially if you limit switch changes to a time when the audio path is not carrying a signal. That's something you should do anyway because there will probably be a sensitivity difference between your various active speaker systems. It's always a good idea to reduce the volume so you don't get any nasty surprises when going from a low-sensitivity system to one with more gain.

The "turn-on" pop from your interface is caused by entirely different reasons then a connect/disconnect "click".

Hope this helps.
Old 4th March 2014
  #5
Lives for gear
 
Richard Crowley's Avatar
 
🎧 10 years
I would use an interlocking set of switches like this...

Passive speaker switcherAlps 4 Pushbutton Switch Assy 4 x 4PDT 3 Interlocking 1 Independent $4 95 Ea | eBay



Using 4 poles means that you can switch balanced stereo signal pairs, and you can have the unused outputs shorted.
That would mute them (keep then quiet) when not selected, and also tend to reduce switching transients.
Old 4th March 2014
  #6
Lives for gear
 
Lotus 7's Avatar
If you haven't seen this old thread already, it may be of interest.
Old 25th March 2014
  #7
Gear Nut
 
🎧 5 years
Hey guys thanks a lot for your responses. Have been away from the internet for awhile, hence the thread revival :P

The switch you linked looks ideal Richard, particularly for its interlocking aspect (disconnecting other switches upon switching). I've just ordered one.

To reiterate. I'm just using a line level signal, and switching it between a hifi amp (unbalanced, RCA in), a driverack (balanced, XLR in) and my studio sub (balanced, XLR in feeding to KH120s). The unbalanced path will have its cold signal tied to ground & all earth wires will be connected to common ground.

Will it help to wire some resistors in as a buffer for the clicks (best place to put them and ohm value?), or will they be insignificant in level? Not worried about the hifi. The driverack should protect the p.a & the sub & kh120s both have in built limiters, though I doubt any clicks would be so high in level as to cause damage?

When a switch is disconnected, will there be an issue with having no load on the corresponding amplifier?

I have a working understanding of this stuff, but definitely do better with help of more knowledgable folks, so again - responses are much appreciated. Looking forward to having a reference switch - so valuable in mixing I think.
Old 25th March 2014
  #8
Lives for gear
 
Lotus 7's Avatar
Switching clicks will normally be very low in level unless you have some electrically "leaking" coupling caps. If a particular input or output has loud clicks, it's usually indicative of a leaky coupling cap or a significant DC offset on an output. In either case the cause should be corrected for reasons beyond just causing "clicks".

On the line-level outputs you're switching, there are no concerns about running the output with no load. It's nothing like running a tube-equipped power amplifier without a proper speaker load on the output transformer (which can create a situation that may cause damage).

Remember, much line level gear: Mixers, EQ's compressors, reverbs are operated all the time with some of the outputs unused. Won't hurt a thing. In many studios, those pieces of outboard gear are connected to patchbays and left running for days with inputs and outputs being connected and disconnected often.

The only major exception is switching/connecting/disconnecting phantom-powered mic inputs which can cause problems and even physical damage to mic pre inputs if switched incorrectly or routed through the wrong type of patchbay. There are no issues switching or leaving mic pre outputs unterminated.
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