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How To Wire an External XLR On/Off Switch Pedal
Old 19th February 2013
  #1
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🎧 5 years
How To Wire an External XLR On/Off Switch Pedal

I need to Wire an External XLR On/Off Switch Pedal. I'm currently figuring to solder ground and nuetral terminals direct from XLR male to XLR female and then run the positive line through a SPST latching foot switch.

Will this work and is there a better way you know of to do this ?
Old 19th February 2013
  #2
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Lotus 7's Avatar
Quote:
Originally Posted by tomana ➑️
I need to Wire an External XLR On/Off Switch Pedal. I'm currently figuring to solder ground and nuetral terminals direct from XLR male to XLR female and then run the positive line through a SPST latching foot switch.

Will this work and is there a better way you know of to do this ?
If it's a balanced connection (a balanced line feed but not a phantom powered mic input), you should interrupt both the positive and negative leads. A balanced XLR connection does not carry a "positive and neutral" signal, it carries balanced positive and negative signal(s) with a common or "neutral" for both plus a shield. Both signal lines must be broken to mute the connection. It's possible to do this with a DPDT switch that breaks the (2) lines and then grounds both of the lines going to the device being fed to eliminate possible noise due to a "open" input.

Addendum: The first schematic attached is for use with line outputs only. It will insure that no overload of the output circuit occurs.
The second schematic is intended for use with Phantom-powered mic inputs, and will mute the audio without causing a switching transient by removing Phantom-power.


SESCOM makes a nice version that can be used for muting or to switch between two sources as an A/B switch.
Radial Engineering also makes one (the ABi) which includes an option for dropping the signal level (adding a pad) as well as complete latching mute.
Building your own is a nice, simple DIY project, and might save a few dollars if you don't cost-out the time it takes.

See attached schematics:
Attached Thumbnails
How To Wire an External XLR On/Off Switch Pedal-balanced-mute-switches.jpg  

Last edited by Lotus 7; 20th February 2013 at 02:46 PM.. Reason: Circuit for phantom powered mic inputs added!!
Old 19th February 2013
  #3
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Do you need it to be latching (like a switch) or is momentary OK?

We wired up push to talk switches, for talent talkback, using 2 pole momentary footswitches.
Old 19th February 2013
  #4
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🎧 10 years
I use the Proco power mute on stage but they make studio talkabck type devices as well
Old 19th February 2013
  #5
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The more accepted method of muting a balanced signal is to short the balanced signal (pin 2 and pin 3) to each other. Especially if this is a microphone signal, and ESPECIALLY if it uses phantom power.

Interrupting the signal path is just asking for problems with noise.
Interrupting the phantom power is GUARANTEED to produce noise problems.
Old 19th February 2013 | Show parent
  #6
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Quote:
Originally Posted by Richard Crowley ➑️
The more accepted method of muting a balanced signal is to short the balanced signal (pin 2 and pin 3) to each other. Especially if this is a microphone signal, and ESPECIALLY if it uses phantom power.

Interrupting the signal path is just asking for problems with noise.
Interrupting the phantom power is GUARANTEED to produce noise problems.

But, of course never short a balanced output if it's a line-level signal coming from a active output which I'm betting is what the OP is wanting to mute since there was no mention of a phantom-powered mic. BUT, as we all know ASSuming anything on this Forum is risky. If it is for a phantom powered mic input, then obviously the provided circuit is not the way to go.

So tomana, what is it? A mic signal or a balanced line output.
Old 20th February 2013 | Show parent
  #7
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🎧 15 years
Quote:
Originally Posted by Lotus 7 ➑️
But, of course never short a balanced output if it's a line-level signal coming from a active output which I'm betting is what the OP is wanting to mute since there was no mention of a phantom-powered mic. BUT, as we all know ASSuming anything on this Forum is risky. If it is for a phantom powered mic input, then obviously the provided circuit is not the way to go.

So tomana, what is it? A mic signal or a balanced line output.
I've never encountered a line-level output that wasn't explicitly or inherently short-circuit protected. Typically we design in series resistance to raise the output impedance and those "build-out" resistors protect the actual circuit from shorting. But it is true that there is no universal, foolproof solution for muting an audio signal.
Old 20th February 2013 | Show parent
  #8
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Quote:
Originally Posted by Richard Crowley ➑️
I've never encountered a line-level output that wasn't explicitly or inherently short-circuit protected. Typically we design in series resistance to raise the output impedance and those "build-out" resistors protect the actual circuit from shorting. But it is true that there is no universal, foolproof solution for muting an audio signal.
True, most designers do include some sort of current limiting, either a series resistor or a current limited op amp, but some high-end mic pres do not. Apparently the designers believe that these devices will be used with appropriate loads and not operated into a short or into a "Y" cable connected to another output. The more expensive and "boutique" devices are the ones most likely to not like being driven into a short. Personally, I think it's always prudent to respect the minimum load impedance specification for any output stage. Particularly as more and more hardware uses small surface mounted devices instead of larger, discrete components, but that's just me.

Re: "..there is no universal, foolproof solution for muting an audio signal": A swift machete blow to the cable is usually pretty effective.
And with some performers fully justified!
Old 20th February 2013 | Show parent
  #9
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🎧 15 years
Quote:
Originally Posted by Lotus 7 ➑️
True, most designers do include some sort of current limiting,
Its not simple current limiting, either. Modern op-amps have very low output impedances and it is very common to insert a series resistor simply to raise the source impedance to something that won't make the cable ring.

Quote:
...some high-end mic pres do not. Apparently the designers believe that these devices will be used with appropriate loads
But what IS an "appropriate load" for a 10-ohm source impedance being driven through some length of 150-ohm cable?

Quote:
I think it's always prudent to respect the minimum load impedance specification for any output stage.
Indeed, but I also think it is prudent to protect your equipment (especially if it is expensive=high-end) against the hazards of the Real World.
And I admit that my presumption of the "use-case" is intermittent short-duration muting such as for a "cough-switch", not something where you run audio into a dead short for hours at a time, etc. But, of course tomana has never returned to clarify his question.

Quote:
Re: "..there is no universal, foolproof solution for muting an audio signal": A swift machete blow to the cable is usually pretty effective. And with some performers fully justified!
Ha! I was thinking of something operational and reversible (and not destructive!)
Old 20th February 2013
  #10
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🎧 5 years
Quote:
Originally Posted by Lotus 7 ➑️
If it's a balanced connection (a balanced line feed or a mic cable) , you must interrupt both the positive and negative leads
I get it. I need to short the positive & negative lines to ground at the amp's input jack. the Shen 150 LT has a constant +12V phantom power applied to the MIC IN jack. Is it safe to short pins 2 & 3 at the amp's input (the equivalent of what is shown in your schematic which, BTW, Thanks!)

Seems I forgot the details:

Shure Beta 57A
Genz Benz Shenandoah 150 LT amplifier

The mic has no on/off switch and I so solo playing/singing and I figured a small footswitch would work ok. I'm wanting the poor man's method, I used to be an electronics repair tech and can etch a PCB, etc if need be.

I bought Switchcraft panel mount XLR (male & female) and have a Laney foot pedal I can chop and drill

Thanks for all the replies {8^D
Old 20th February 2013
  #11
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No, you do NOT want to short either 2 or 3 to ground if phantom power is present!!! NOT!!

You want to short 2 and 3 to each other, but NOT to ground.

There is no problem shorting the output of a microphone. But shorting TO GROUND the input of a mic preamp with phantom power on it is practically guaranteed to cause major problems.

I would simply wire the switch across pins 2 and 3. Then whenever 2 is connected to 3, the audio is going nowhere, but the phantom voltage is unaffected.
Old 20th February 2013
  #12
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As Richard correctly stated, just connect as SPST switch across pins 2 & 3. When the switch is closed, the mic will be shorted out and therefore muted. The circuit I posted was intended for a line output or a dynamic mic ONLY and should NOT be used if there is any phantom power on the input.

The circuit in post #2 can be used between the output of a mic pre and the following input.
Old 20th February 2013
  #13
S21
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There isn't a better general purpose option than shorting 2&3 together.

When you start heading down the purist path of breaking both 2&3 and terminating each direction in the expected impedance other stuff bites - phantom power doesn't work, etc
Old 20th February 2013
  #14
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I amended the shorting switch circuit to my original post just in case someone sees that schematic and does not read the whole thread.
Old 20th February 2013 | Show parent
  #15
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Quote:
Originally Posted by Richard Crowley ➑️
No, you do NOT want to short either 2 or 3 to ground if phantom power is present!!! NOT!!

You want to short 2 and 3 to each other, but NOT to ground.

There is no problem shorting the output of a microphone. But shorting TO GROUND the input of a mic preamp with phantom power on it is practically guaranteed to cause major problems.

I would simply wire the switch across pins 2 and 3. Then whenever 2 is connected to 3, the audio is going nowhere, but the phantom voltage is unaffected.
Quote:
Originally Posted by Lotus 7 ➑️
As Richard correctly stated, just connect as SPST switch across pins 2 & 3. When the switch is closed, the mic will be shorted out and therefore muted.
This is exactly how we wired our talent talk-back switchs.
Old 21st February 2013 | Show parent
  #16
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tomana's Avatar
 
🎧 5 years
Quote:
Originally Posted by Lotus 7 ➑️
I amended the shorting switch circuit to my original post just in case someone sees that schematic and does not read the whole thread.
Excellent ... I have a SPDT footswitch so I will not need to buy a DPDT. Thanks for all the generous replies
Old 22nd February 2013
  #17
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It worked great! Just wanted to say thanks
Old 15th December 2013
  #18
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🎧 5 years
Thanks for this post ... it helps with a problem that I am now facing with two lectern condenser mics. Was wondering if its not best to wire the normally open terminal (top) to Pin 3 instead of leaving it open. This should reduce the chance of a pop when un-muting.
Old 16th December 2013 | Show parent
  #19
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Quote:
Originally Posted by bcopeland ➑️
Thanks for this post ... it helps with a problem that I am now facing with two lectern condenser mics. Was wondering if its not best to wire the normally open terminal (top) to Pin 3 instead of leaving it open. This should reduce the chance of a pop when un-muting.
It won't reduce the chance of a pop, or do anything else for that matter.
Old 16th February 2019
  #20
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Will Shorting pins 2 and 3 together for an extended time cause any problems? Say i leave the pins shorted with a toggle switch overnight or for drastic sakes for over a week? i plan on making a DIY mice mute for a Rode Procaster(xlr versionn of course) and it does not require phantom power. and i wanted to make a box that has both momentary AND toggle mutes. that way I could quickly mute my mic to sneeze, cough, etc and be right back in, or to completely mute my mic if say my roommate came in to talk for a few minutes, this would Solve the problem for me of not having to mute the mic in software as i much prefer hardware diy solutions.
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