how to use small mic from camcorder

Two kinds of mics... a dynamic mic is a coil of wire around a magnet... should be able to read ohms across the red and black... an electret mic needs 9vdc to run the fet preamp which buffers the electret mic element. PC mics have a 3 conductor tip-ring-sleeve stereo plug and jack. tip=audio, sleeve=gnd, I guess that leaves ring=9V?? Got a scope? Go 'woooooo!' into the mic and see what comes out the wires.

There's way more than two types of microphone, but those are the two that are commonly used these days.

Three more are:

1. Condenser (_not_ electret) that used a macro-sized sound-variable condenser, and needed about 100V of bias.

1. Carbon mic. This type modulates the resistance. The sound quality isn't good, the carbon granules would pack, but it was a good enough communications microphone that there are probably still millions in service in older telephone sets.

2. Just about any sensitive measuring instrument that you _don't_ want to use as a microphone (sigh).

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I don't know about the mic in a camcorder, but your PC soundcard expects a microphone with an internal amplifier. See:

First, a pedantic point: I assume you are soldering to a *plug* (male part), not to a *jack* (which is the female receptacle on the sound card).

Sound cards assume you have an electret mic. This type of element typically looks like a small aluminum cylinder about 1/4 inch in diameter and maybe 1/4 inch tall. These all have internal preamps that need power. The card's jack supplies about 5V through the Right channel of the Mic In connector. (Which is why you never get stereo Mic inputs on these cards.)

You mention that the mic element has only 2 connectors, but note that it is quite common for the case to be the ground. Sometimes you can see the connection going from one of the pins to the case... I'd guess the black one. Assuming that is true, you might need to wire a resistor between the Right channel on the plug and the red connection on the mic (which also goes to the Left channel on the plug). Resistor value should be in the 2k to 4.7k range, typically.

Note that you have to use Mic In on the sound card. Line In not only doesn't have the power on the Right channel, it also doesn't have a mic preamp to supply the gain you need for an electret.

If the mic element is from a very old device, it *might* be dynamic, but I seriously doubt that. Dynamic mic elements do not need external power, so don't connect anything to the Right channel, just the Left and ground. They typically look exactly like earphone elements, which they essentially are. This may give you a clue for an alternate plan: If you have an old pair of headphones, just cut them up and extract the elements.

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!

these cards.)

Hi Bob,

Thanks for the really help response. It was interesting to hear the comments about the comp line in etc.

The stereo mic actually worked on my iRiver (portable mp3 player with line in). I recorded something and it sounded fine ... obviously the signal would have been amplified inside the player.

What I'm trying to do is hook up one of these miks to an ipod dock connector, so I could then connect it to my ipod (ipod touch) and record audio from it. I've been hoping that it doesnt need power as the idea was to try and fit it into the little connector plug. I know which pins are for line in etc.

I'm not sure though if the ipod touch's line in will have a preamp inside to amplify the signal? Would the stereo mic (which worked without power on the iriver) have too weak a signal for the ipod?

Would you mind if i emailed you pictures of both mikes? If so, please email me to gmail and then I can send them through. Your post was very interesting - I dont know a great deal about mics.. just about the plug etc, but would love to learn about them through this problem.

Also, in terms of how the mic is powered (assuming this stereo mic must be dynamic then)... does it basically generate its own current, where the sound waves hit the diaphram which moves the magnet (must be a tiny tiny magnet) through the coil, producing the current?

Just to reiterate, this is one of those tiny mics from a camcorder (quite small).

Thanks, Andrew

I have no experience with iPod or iRiver, but Line inputs typically expect around 1 VRMS maximum input, and Mic inputs are typically 10 times more sensitive. So the mic will surely be too weak for Line inputs.

I'm on dial-up, so big photos are a problem. But if you can describe the mic element, it should be pretty easy to tell if it's dynamic or electret. I'd be *very* surprised if it was dynamic.

You have the concept exactly right, but the details reversed: The coil is what is attached to the diaphragm, and moves through the field of a stationary magnet. Take apart any old speaker or headphone (except for rare electrostatic types) to see how this works. The coil can be made very light to respond to soft sounds and high frequencies, while the magnet can be made large to increase sensitivity or loudness.

Sure sounds like electret to me! Dynamic mic elements tend to be 1/2 inch or more in diameter. They often have a clear flimsy dome over them. Electrets never do... usually a thin piece of felt over the end of the aluminum case, or maybe a single hole (or a pattern of holes) in the aluminum.

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!

I think it's fair to assume it is electret, and then using the ohmmeter as someone suggested will verify. Looking for polarity markings on the actual microphone would be another giveaway. So would seeing a circuit board, however small, where the wires come out.

All the recent things I've taken apart that have built in microphones used electrets. I think they were relatively common for internal microphones even thirty years ago. They are common enough that anything else would be an exception.

Michael

Hi Michael and Bob,

Thanks for both your really helpful replys. I'm learning alot here with your help, so its much appreciated.

Try these.... this is the mono mic -

(i've since soldered it to a mono plug) Stereo Mic - (likewise to a stereo plug)

BOTH of these have worked when connected to my iRiver line-in (that is, I've recorded using ext. mic and they've sounded fine). Are they electrect? If so, then how would they work with the iRiver given there was no power? (doubt there would be phantom power from the line in jack of the iriver either).

Is it that electret mic's will work without power, but the JFET won't amplify the signal at all at its not being powered? Or could these both not be electret's?

I've tried both connecting each into the mic line-in connection of the computer, but nothing... no signal is recorded at all.

Given the iPod is a portable music player - if I was to take one of these, say the mono, and then solder the wires to the line in left and ground on the dock plug (and then connect it to the ipod), do you think the signal be strong enough to be recorded?

Is there an easy way to measure the output of the signal from the mic(s)?? My father, who passed away two years ago was an electronics engineer, so he has a scope and other stuff downstairs in the workshop. (I never did electronics but learnt a fair bit by watching him, through physics etc).

Thanks guys! Andrew

Can't tell about the stereo unit, but the mono mic does indeed look like it's dynamic... looks exactly like the driver from a headphone! All the electrets I have see are in small aluminum cans, so unless this black plastic is just a housing for a small aluminum can, I'd go with this being dynamic. (Which is surprising.)

Can you see inside this unit or the stereo unit to look at the actual elements?

An electret mic element needs to work into an "infinite" impedance (OK, "really, really high impedance"), which the JFET provides. So I don't think it would work without power. (I just now connected an electret to the scope and got absolutely nothing, as expected.)

Seems easy enough to test, and won't hurt anything.

If you've got a scope, it is easy to test if a dynamic mic is working at all. Just connect the scope probe tip and ground clip to the two mic connections (doesn't matter which is which), and make some noise. As to whether it is going to be loud enough, that depends on what it's going into. You should be seeing something like +/- 100 mV when you whistle into it directly. Fed to a Line input, this would probably give a pretty meager result... 20 dB lower than what that input expects, but possibly useful for some things.

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!