[ARC5] [Milsurplus] Carbon mic pops

[J Mcvey]

C21 and C16 are basically "ripple filters" for the power supply noise.R37 provides current limiting. 
C-16 will be at full charge (6V) and this same 6v will be the open circuit voltage at the mike before it is keyed, the RC time constant will not affect the mike keying because it is already at 6v.

The mike resistance and the leakage inductance of the primary will have a time constant, though.
This brings the discussion back to the what's the characteristics of the mike?Also, a carefully selected cap across the primary should minimize the click-even if the mike is causing the problem.



 

    On Wednesday, November 30, 2016 6:35 AM, AKLDGUY . <neilb0627 at gmail.com> wrote:
 

 R-37 and C-16 have an RC time constant of 50 mS. Check that a) both are fitted b) C-16 is good. You can tell whether it's good or not by charging it and watching the voltage across it decay when the source voltage is removed.
73 de Neil ZL1ANM



On Wed, Nov 30, 2016 at 8:34 PM, Hubert Miller <Kargo_cult at msn.com> wrote:

What’s the voltage available to the mic element BEFORE the microphone is switched in, has mic current flowing?In other words, does it soar with no ( mic ) load?-Hue From: Milsurplus [mailto:milsurplus-bounces@ mailman.qth.net]On Behalf Of hwhall at compuserve.com
Sent: Tuesday, November 29, 2016 10:45 PM
To: arc5 at mailman.qth.net; milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] [ARC5] Carbon mic pops Attached is the schematic of the mic circuit & amp that I'm looking at. The mic internal wiring looks like just a set of PTT contacts in series with the carbon mic button + the small cap across the mic button.

The primary of T-4 has no current thru it until one of the mics is keyed, then suddenly current flows thru primary & carbon mic, inducing a transient in T-4 that appears as a loud initial pop in the headphones. I don't see how they prevented this pop from happening every time a mic was keyed.

By hitting Send I'm about to remind myself whether these forums allow images attached.  :-\Wayne
WB4OGM 
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