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PostPosted: 20 Feb 2018, 06:57 
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Joined: 20 Feb 2018, 03:49
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Hi there, im new here! My name is Rob and Im an audio technician. I've discovered this forum while searching for the follow solution:

Im looking for a version of this circuit (which eliminates the 'pop' caused by DC voltage powering an electret condenser) that works with a NO switch.

Attachment:
anti pop circuit with NC switch.png


Is this possible?

Im using a generic walkie talkie covert PTT mic, which I will terminate appropriately into a lectrosonics SMDB transmitter. (circuit diagram on page 11); http://www.lectrosonics.com/europe/phoc ... es_Man.pdf

Thank you in advance!!


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PostPosted: 20 Feb 2018, 18:05 
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Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Hi and welcome!

What I see here is a circuit that shorts the AC and the DC difference that causes the *pop* is bled-out by the 100K resistor.

How well 100uF will work depends on the output imedance of the microphone. IIRC, most electret condensor built-in preamps are about 47 to 100 ohms. So you'll need 10 ohms or less reactance at the lowest frequency. For voice communications on a talkie, this is usually cutoff at 300Hz. Use 100Hz for good measure.

A quick check on a reactance calculator says 220uF will work.

This isn't a HiFi circuit, so best linearity isn't needed, but low ESR on the cap is. A Panasonic FM series would be my first go-to.

If the leakage is too much and you still get a *pop* after cap break-in period (~50 hours), my second go-to would be a Nichicon UKL low leakage.

Cheers!

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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PostPosted: 21 Feb 2018, 11:25 
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Joined: 20 Feb 2018, 03:49
Posts: 2
Geek wrote:
Hi and welcome!

What I see here is a circuit that shorts the AC and the DC difference that causes the *pop* is bled-out by the 100K resistor.

How well 100uF will work depends on the output imedance of the microphone. IIRC, most electret condensor built-in preamps are about 47 to 100 ohms. So you'll need 10 ohms or less reactance at the lowest frequency. For voice communications on a talkie, this is usually cutoff at 300Hz. Use 100Hz for good measure.

A quick check on a reactance calculator says 220uF will work.

This isn't a HiFi circuit, so best linearity isn't needed, but low ESR on the cap is. A Panasonic FM series would be my first go-to.

If the leakage is too much and you still get a *pop* after cap break-in period (~50 hours), my second go-to would be a Nichicon UKL low leakage.

Cheers!


Thanks for the reply! So the issue is not with this circuit - it works fine as it is with a NC switch.

I need it to work with a NO switch somehow


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PostPosted: 21 Feb 2018, 13:36 
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Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Sorry, I missed that last part.

So, you need an auto-mute on power up?

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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