[Milsurplus] [ARC5] Carbon mic pops

[AKLDGUY .]

Ah, OK, it was not at all clear where the supply to the mic was switched on.
I assumed it was in the lead to the resistor & 50uF cap, in which case
their time constant would have acted
to smooth the abrupt turn on.

73 de Neil ZL1ANM

On Thu, Dec 1, 2016 at 4:00 AM, J Mcvey <ac2eu at yahoo.com> wrote:

>
>
>
> 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
> <milsurplus-bounces at 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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