PTT Remove Microphone Pop

Thread Starter

CT_Charlie

Joined Nov 5, 2020
8
Hi there

Sorry for a repeated thread but I have read the other posts and tried their solutions with no luck so far. I don't have much experience with analogue circuits so please bear with me and I apologise if it cannot be done.

The background is that I have created a circuit that adds a PTT switch inline of a Dell headset.
It is simply a SPST PTM (NO) switch in series on the Mic + line. When pressed this is obviously inducing a 'Pop' which causes Windows to adjust the microphone level.
This can be stopped in the settings but the product will be used in a military environment, meaning the end user will not have access to these settings.

The input to the PC is a standard 4 pin audio jack going through a splitter, the 4 lines are:
Left speaker
Right speaker
Mic +
Gnd

Please see the basic schematic below.
1604592700729.png

I have no access to power so cannot use an Op Amp.
Any ideas on how I could remove the 'Pop' noise?

Many thanks for any answers in advance
Charlie
 

RPLaJeunesse

Joined Jul 29, 2018
158
I assume this is an electret microphone. Electrets require a bias voltage to operate, and the source supply is of necessity higher than the bias voltage. When you open the switch you dump a huge positive spike into the mic preamp, close your switch and you dump a huge negative spike (pop) into the mic preamp. You might try to change to a SPDT switch set up to select either the microphone or a resistor that drops the exact same voltage as the microphone. Hitting "exact" could be problematic. The switch won't transfer perfectly, so that will still allow some pop. FWIW you are attempting a simplistic solution to your goal, without understanding the limitations and tradeoffs. You may not like the tradeoffs, but you appear to have no choice but to live with them.
 

AlbertHall

Joined Jun 4, 2014
11,147
You could use a circuit as below this makes sure that there is no DC voltage either side of the switch so no pop when it closes or opens. I applied this to the mic switch on a university radio station back in the days of yore. The capacitors should be big enough to pass the lowest frequencies (depends on the impedance of the circuit. The resistors can be quite big just so the leakage of the capacitors drops no significant voltage across the resistors.

1604612601984.png
 

Thread Starter

CT_Charlie

Joined Nov 5, 2020
8
Thank you for your replies.
It doesn't seem to be an electret microphone because it does not have a voltage supply?
I will try each circuit to see if I can remove the DC spike and will post the results.
Thanks
 

Thread Starter

CT_Charlie

Joined Nov 5, 2020
8
You could use a circuit as below this makes sure that there is no DC voltage either side of the switch so no pop when it closes or opens. I applied this to the mic switch on a university radio station back in the days of yore. The capacitors should be big enough to pass the lowest frequencies (depends on the impedance of the circuit. The resistors can be quite big just so the leakage of the capacitors drops no significant voltage across the resistors.

View attachment 221543
Hi
Thanks for the reply. Do the capacitors need to be polarised and do you have a rough estimate on what size they would need to be?
Thanks
 

Dodgydave

Joined Jun 22, 2012
9,920
Looks like it has a built in noise cancelling circuit, that uses two mics and inverts the background noise and cancels it out, .
 

Audioguru again

Joined Oct 21, 2019
2,878
If the mic is a dynamic type then why does it POP when it is shorted during muting?
Maybe your computer or whatever the headset is used with, assumes that it has an electret mic and sends power out to the mic and your PTT switch passes the audio and unfortunately also passes the DC. Then your PTT switch needs to be moved and maybe a coupling capacitor must be added to pass the audio but not affect the DC.
 

Thread Starter

CT_Charlie

Joined Nov 5, 2020
8
For a dynamic mic I would suggest the capacitors should be 22uF and, at least for the microphone side, should not be polarised (as there is no voltage to polarise it) so likely the cheapest will be ceramic. Try 47k for the resistors - this is not critical.

e.g. https://www.mouser.co.uk/Passive-Co...tors-MLCC-SMD-SMT/_/N-bkrdv?P=1z0wrkiZ1yx4atv
Thanks for you help. I tried the circuit using this cap GRM31CR61E226KE15L and I am unable to get any sound out on the PC now. Any ideas?
 
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