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PTT for Lectro


Trey LaCroix
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Maybe not exactly what you are asking but when I needed a PTT for a Voice of God setup, I simply bought a hand-held PTT CB mic on eBay and wired it with an XLR.  The directors just threw the Lectro Plug-on in their pockets and yelled into a self-powered PA speaker.  Worked great.

 

D.

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I should have elaborated a bit more. I’m setting up a talkback system for my boom op and figured using one of my old um400s with a cheap headset mic would be the simplest solution for me.

 

I’d like to keep the comm return routed to my headphones but don’t want to hear it open all the time. So I believe the only way to do this would be to put a PTT button I line from the mic to the TX.

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Are you looking to add a switch to an electret lav or do you just want PTT on a dynamic handheld type mic?

 

With an electret lav you need to worry about the "thumping" of mic power, Shure recommends a 1000uF, 6Vdc for 600 ohm mic (close enough for most lavs) obviously, the connector end depends on your transmitter.

 

Basically, what this circuit does is that when the switch is engaged, the capacitor shorts out the AC voltage (audio) so the mic isn't making noise, but it doesn't short out the DC voltage (mic power/phantom) so the mic still stays energized.

 

I haven't yet built one of these on my own yet, but this is my research and plan.
 

zddP7.png

4 minutes ago, Trey LaCroix said:

I should have elaborated a bit more. I’m setting up a talkback system for my boom op and figured using one of my old um400s with a cheap headset mic would be the simplest solution for me.

 

I’d like to keep the comm return routed to my headphones but don’t want to hear it open all the time. So I believe the only way to do this would be to put a PTT button I line from the mic to the TX.

If you don't care about the pop in your coms line (an aggressive filter can take care of most of it) just wire a walkie mic as you would with a lav.

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3 hours ago, Shastapete said:

Are you looking to add a switch to an electret lav or do you just want PTT on a dynamic handheld type mic?

 

With an electret lav you need to worry about the "thumping" of mic power, Shure recommends a 1000uF, 6Vdc for 600 ohm mic (close enough for most lavs) obviously, the connector end depends on your transmitter.

 

Basically, what this circuit does is that when the switch is engaged, the capacitor shorts out the AC voltage (audio) so the mic isn't making noise, but it doesn't short out the DC voltage (mic power/phantom) so the mic still stays energized.

 

I haven't yet built one of these on my own yet, but this is my research and plan.
 

zddP7.png

If you don't care about the pop in your coms line (an aggressive filter can take care of most of it) just wire a walkie mic as you would with a lav.

Hi Peter,

Your circuit will give you about 40 dB of attenuation at 160 Hz assuming that the electret in parallel with the transmitter input is about 1k of load resistance, with more attenuation at higher frequencies and less at lower frequencies. There will usually a faint tick when the switch is closed as the capacitor (use a tantalum cap) will leak a tiny amount of current and develop a small voltage across the 100k resistor. Since all of this is in an RF field, you will also get a faint tick as the switch changes the effective RF length of the mic cable. None of these will be a problem in your application. I am including a link to a pdf with the complex circuit we ended up using to make the switch totally silent.

https://www.lectrosonics.com/All-Accessories/product/mute-2.html#data-sheet

 

Happy experimenting,

Larry F

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