how to use small mic from camcorder

[andrew_h]

Hi all,

I took a mono mic out of an oldish camcorder we had, and wanted to
then solder it to a jack and see if it'll work to record to my PC.
However, I've had some problems and questions that I'd appreciate if
someone could help out with.

Firstly a question - sorry if it sounds stupid - don't these little
mics need power? there is just the red and black lead from them, which
i would assume is mono sound channel (red) and ground (black).

Anyway, I got a new mono jack. I soldered the red cable to the tip
(end bit of the jack) and then the black cable to the sleeve (for
ground). When I connect it and try to record, nothing at all is
recorded. (when I say tip, I dont mean literally the tip, but to the
area where cables are meant to be soldered for the tip channel).

Another question... the output from this mic would probably be really
really weak wouldnt it? How could I measure the output from it? I
tried using a multimeter, on a millivolt setting, and then tapping the
mic etc. but there was nothing read. It was connected black lead to
the black, and red to red.

I tried all this above with a stereo mic, also taken from an oldish
camera. This was different in I used a stereo jack, and connected one
set of red and black to the tip and sleeve, and then the second red
(right channel) to the ring and the black from that again to the
sleeve. Again, nothing could be recorded.

Does the signal need to be amplified before anything will be picked up
when recording to the comp? I'm not looking for loud volume or
anything, but just wanted to see if any signal would be picked up (it
wasnt).

What am I doing wrong? Someone please help me out - thanks! Can e-
mail me to andrew.heyn@gmail.com or post on this, thanks a bunch.


Cheers, Andrew

 

[BobG]

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.

 

[Tim Wescott]

On Thu, 22 Nov 2007 21:03:01 -0800, BobG wrote:

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.

2. 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.

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

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

 

[mc]

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

http://www.ai.uga.edu/mc/SoundCard.pdf

 

[Bob Masta]

On Thu, 22 Nov 2007 19:46:11 -0800 (PST), andrew_h
<andrew.heyn@gmail.com> wrote:

Hi all,

I took a mono mic out of an oldish camcorder we had, and wanted to
then solder it to a jack and see if it'll work to record to my PC.
However, I've had some problems and questions that I'd appreciate if
someone could help out with.

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
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

[andrew_h]

On Nov 24, 12:23 am, NoS...@daqarta.com (Bob Masta) wrote:

On Thu, 22 Nov 2007 19:46:11 -0800 (PST), andrew_h

andrew.h...@gmail.com> wrote:
Hi all,

I took a monomicout of an oldishcamcorderwe had, and wanted to
then solder it to a jack and see if it'll work to record to my PC.
However, I've had some problems and questions that I'd appreciate if
someone could help out with.

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 electretmic. This type of element
typically looks like asmallaluminum 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 theMicIn connector. (Which is why you never get stereoMicinputs on these cards.)

You mention that themicelement 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 themic(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 useMicIn on the sound card. Line In not only
doesn't have the power on the Right channel, it also doesn't have
amicpreamp to supply the gain you need for an electret.

If themicelement is from a very old device, it *might* be dynamic,
but I seriously doubt that. Dynamicmicelements 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
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

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

 

[Bob Masta]

On Fri, 23 Nov 2007 17:50:50 -0800 (PST), andrew_h
<andrew.heyn@gmail.com> wrote:

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?

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.

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.

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.

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?

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.

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

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
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

[Michael Black]

Bob Masta (NoSpam@daqarta.com) writes:

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.

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

 

[andrew_h]

On Nov 25, 2:37 am, et...@FreeNet.Carleton.CA (Michael Black) wrote:

Bob Masta (NoS...@daqarta.com) writes:
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.

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 - http://www.flickr.com/photos/8040070@N07/2060785219/
(i've since soldered it to a mono plug)
Stereo Mic - http://www.flickr.com/photos/8040070@N07/2060785229/
(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

 

[andrew_h]

Also, re using ohm meter - I tried connecting a multimeter on the
lowest ohm setting to the red and black leads of the mono mic, but
nothing came up (just stayed as OL).

 

[Bob Masta]

On Sat, 24 Nov 2007 20:04:06 -0800 (PST), andrew_h
<andrew.heyn@gmail.com> wrote:

Try these.... this is the mono mic - http://www.flickr.com/photos/8040070@N07/2060785219/
(i've since soldered it to a mono plug)
Stereo Mic - http://www.flickr.com/photos/8040070@N07/2060785229/
(likewise to a stereo plug)

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?

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?

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.)

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?

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

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).

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
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!