Impedance???

[Scipio Kid]

Using Deoxit on the PTT switches, I've recently gotten several problem mics to work like new. But in testing them I found two that seemed to have (my theory) much higher impedance than the others. They're both Cobra mics, one is clearly an older style, but when compared to any of the other 4 pin mics they are noticeably quieter. They work and sound great but they're very quiet. On a radio where I'd normally run the built-in power mic at half, I have to turn these to max to be heard. But I get all kinds of feedback (on the talk-back) with a normal mic under the same conditions.

So the question is, do some radios require a higher impedance mic and if so, did Cobra make some of these mics for those radios? Or, do I just have a couple of mics that no longer work right? I always thought most mics, especially the common 4-pins, were all pretty much the same from radio to radio or even brand to brand.

A while back, I had the same problem with some Radio Shack mics. I took a little TRC-465 radio with me on a road trip and it seemed to work great but others kept telling me to turn my power mic down, that I was way over modulated. Well, of course, there's no adjustment on the mic or the radio. Later, I listened to it on another radio and that's exactly how it sounded. I have a mic tester so I pulled out every similar mic and tried them all and I found 4 of the mics sounded great, but two sounded like overmodulated power mics. Tried them on different radios too and got the same result so I'm assuming Radio Shack made a few radios that needed lower impedance mics than the rest of their products. Sort of the opposite theory I came up with for the Cobras.

Anyone have any idea if my theories are even close to reality? Maybe mics just go bad and you chuck them. I don't hardly ever chuck anything.

I had the same kind of question when I adapted an Electro-Voice 622 for my Washington. Something I never could have done without the expert advice of Mr. MDYoungblood. At first, I thought the 622 was too quiet. But it's a noise-cancelling mic and if you're not close enough, it sounds quiet. I tested the original hand-held against the 622 and found, under normal circumstances the 622 is actually a little louder and less tinny than the stock mic. But if you hold it 6" away, the stock mic pics up your voice better, where the 622 loses about half the volume it had when you were close. So that's not the same as with the Cobra and Realistic mics. They definitely perform at higher and lower volumes.

Any thoughts?