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Mic preamp design help...

Microphone Information Wiring etc, or if you just need help with choosing a good microphone for your radio.

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BiggieJ
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Mic preamp design help...

Post by BiggieJ » Thursday, 03 September 2015, 7:18 AM

Hi...

I'm new here and would like to say hello to all :)

I am wondering if someone could/would provide me with a link (or design) to a simple circuit to create a radio powered, power microphone for a CB Radio?
(One you have experience with. Not one from a Goo search, I can do that) :)

It would be nice if it would fit into a mic but inside the radio would be fine as well. Or maybe plug in, in between the mic and the radio to make it portable.

I'm wondering if a condenser mic design would be too tinny? I personally kinda like a bit tinny :)

So basically I am looking for a way to power a stock mic to make it a power mic. Or even start from scratch.

If it is any help, for those of you who know what the old D104 sounded like, that is what my target design would sound like,


Thank you for your kind consideration and help,
John


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Re: Mic preamp design help...

Post by 231 » Friday, 04 September 2015, 22:18 PM

Hi John,

I've run both mobile & lollipop D104's over the years and all of them ran on 9v provided by a battery inside the mic if you recall. I don't ever recall seeing any of the radios providing power for that (or any other) power mic? Have you considered looking into doing a simple EQ external of the condenser mic you are thinking? I don't have direct experience making a circuit to what you are thinking (or rather what it sounds like you are thinking?)...can't say as I ever heard anyone do that before either?

I run a W2IHY EQ/Noise Gate on my ham gear with a low impedance cardoid mic (Audio-Technica ATR30 boom mic) and get nothing but compliments on it sounding broadcast quality. But really I can't take any credit...between the rig, mic, and EQ it's just a good combo'. On my CB's, with few exceptions I've always stuck with the D104's because to me they had lots of punch and sounded like the people who ran them. That is provided their audio settings were not set too high and running around 100% mod peaks.

Depending on the response(s) you get here, consider looking at the audio circuit on the Uniden Pro510xl. Seems to me the mic needed to be specific because the amplification was in the radio, not the mic. And replacing the stock mic with a plane Jane stock mic or non-amplified mic (i.e. D104) or not a Pro510 stock mic would result in super low audio (like 30% peaks tops...next to impossible to hear unless you turn the volume way up). That radio might hold the key to at least an idea that might work? Just a thought.

Best of luck and let us know what you come up with...or consider trying. Or, better yet the results.

231

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BiggieJ
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Re: Mic preamp design help...

Post by BiggieJ » Saturday, 05 September 2015, 7:18 AM

Hey 231, thanks for the reply...

I think I have about decided to just run a Electret Condenser Mic element circuit using phantom power from the radio.


73's
J

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Re: Mic preamp design help...

Post by Buzzweiser » Saturday, 05 September 2015, 15:33 PM

A microphone amp circuit is a pretty simple design. You can make one on a small breadboard and mount it inside the radio if you have room. The circuit for the old turner hand mike is pretty simple as is the astatic circuit. You could power the circuit directly off the input power for the radio and step it down with a diode and resistor to make it 7 - 9 volts. That way you won't be pulling power directly from the radio board circuit. From that point it's merely changing a few wires coming from the female mike input to run thru the amp circuit first. You'll have to experiment with different mike elements probably to get the sound you are looking for. Certain condenser elements can sound good. I know one gentleman who liked using the condenser element from the old 49Mhz cordless phones. The only downfall to mounting the board inside the radio would be the ability to adjust the VR pot. With that in mind you may want to consider an external box and use VR pots with external knobs. If you decide to go with an external box the astatic 1104C circuit would be a good circuit to mimic as it also has tone control.
Dave the Old Fogie 656 Dayton, Ohio
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BiggieJ
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Re: Mic preamp design help...

Post by BiggieJ » Sunday, 06 September 2015, 5:00 AM

Thank you Buzzweiser...

J


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Re: Mic preamp design help...

Post by TheCBDoctor » Tuesday, 08 September 2015, 9:04 AM

Hi BiggieJ

Rather than building a pre-amp Mic gain circuit you would be better of using a good power Mic with an EQ in line. You didn't mention what type of radio you plan on doing this too. You can increase the gain of the pre-amp by increasing the gain of the existing pre-amp circuit by increasing the capacitance of the emitter by pass capacitor.

This would be the capacitor in parallel with the emitter resistor. The DC voltage does not change the bias voltage drops to turn the transistor on, but increases the AC gain. Look up emitter bypass capacitor in your search engine.

Respectfully as always

Rick

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Rick, The CB Doctor


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