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Old Nov 23, 2014, 02:08 PM
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Help!
Perfecting a DIY Electret Microphone Circuit.

I just put together an electret microphone circuit to allow for some onboard audio during FPV, however, there are a couple of problems that need sorting.

The first problem is that it picks up moving air, i.e. blown air, but it is very poor in picking up speech, be that directly from myself or speakers. Even with my TV's volume at full whack the verbal is minimal compared to me blowing on the mic.

The second problem is that there is constant, varying RF noise. The best way to describe it would be as an increasing/decreasing pitch/whine, somewhat like a very quiet jet engine or listening for a transmission while stranded on a Pacific island during WW2.
Below are a couple of pictures, showing the circuit and my setup. The only thing that I've had to change is that I have had to use a 2K7 resistor instead of a 2K2.
The Tx is a Best Offer Buy 700mW unit.

Can these problems be cured?

Cheers,
Tom.



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Old Nov 23, 2014, 08:41 PM
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Good luck!
Even the pros with $1k+ gear and professional training have a LOT of trouble with wind noise.
If there was an easy solution we wouldn't hear wind noise drowning out weather forecasters, hunting guides, etc.. They usually only get even that good of audio by using a good mike with a good windscreen very close to the audio they're trying to get.

I'd try various windscreens. (The foam piece over mikes) You could also put it in a tube with a windscreen over the end. I don't think you'll ever get very good audio, but I'm sure with some effort you can make major improvements over a bare electret.

You might try something like the ones that look like a mike stuffed into a dead cat on the end of a pole. I think the idea is that the soft hair is too soft for the wind to whistle against.
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Old Nov 24, 2014, 01:24 AM
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Jakestew,
You've misinterpreted what I'm saying. The problem is that when it is on the bench and I'm up close and personal it has very poor gain(?) when using speech but if I lightly blow into it there is no problem in hearing that on the TV speakers.

Tom.

p.s. the mic will be internally mounted on the aircraft just to monitor motor and battery alarm function, external wind noise won't be much of an issue.
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Old Nov 24, 2014, 02:09 AM
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Well, the cap looks way too large and I'm not sure why the 10k is there.
I'd try some of the many simple preamp circuits out there.
What are you using for amplification currently?
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Old Nov 24, 2014, 04:10 AM
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My circuit was cobbled together from what I could strip from some computer power supplies, hence the 2K7 resistor.
Yes, the 10K resistor doesn't seem to make any difference, I'll no doubt remove it.

What do you suggest for the capacitor?

The only applification I'm using is simply a 15" portable TV, sat on my bench, with the video Rx plugged into the A/V sockets.

Tom.
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Old Nov 25, 2014, 04:36 AM
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The TX must not be providing any amplification on the audio. You'll probably need a preamp circuit. Don't worry, it's just 3-4 more simple components.

I've seen values from 0.1-4.7uf for the cap. Try something in that range.
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Old Mar 17, 2015, 12:33 AM
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Did this ever evolve?
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Old Mar 17, 2015, 01:48 AM
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If you google "mic preamp ic agc" you can find several ICs that provide amplification, bias voltage, and automatic gain control.
You'd really need something like that to pick up decent audio when you have loud wind noise and still want to pick up some sounds when the wind/motor is off.
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Old Mar 17, 2015, 04:10 AM
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I gave up on it and bought a 12V mic set off the web. Works perfectly now with my setup.

Tom.
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