# A very basic question about a || circuit

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#### chilinski

##### New Member
I have a microphone (some unknown electret in a Cobra handheld mic) that is connected to a 1/8 mono jack like this:

+---------------------------------------- tip +5V from CB/FRS
ECM | R1 .66K | C1 103
| |
----------------------------------------- shield

The resistor and capacitor are in parallel. I want to replace the ECM with a noise-cancelling ECM. Is this just a matter of soldering the n/c ECM in place of the old ECM? Are any changes to R1 and C1 required? How about a really basic question: what is the practical effect of R1 and C1 in parallel? I can find explanations about what it does to voltage/capacitance/impedance from a mathematical standpoint, but what does it really do in a practical application? In other words, why can't you just connect the microphone without the resistor and capacitor?

#### chilinski

##### New Member
Okay, I think I finally got the words in the right order in the search engine to get the explanation. Tell me if I'm wrong.

This is a low pass filter, right? The capacitor provides a path for high frequency signals to ground, thereby filtering them out and not letting them go back to the radio, right? The values for R1 and C1 have nothing to do with the electret itself but with the level of frequency you want to pass, right?

This is pretty elementary, right? A waste of time to even ask here, correct? But believe it or not, it took me several days to finally find a "practical" explanation instead of one that was based in mathematics that I have long forgotten.

But, of course, this leads me to another question. Is this filter already built into a noise-canceling microphone, so that adding R1 and C1 to a n/c electret would be needless (and probably contrary)?

I'm sure I'll stumble on the answer myself in a couple of days, and I'll be able to post another reply to myself just for the record.

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