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Sci.Electronics.Basics -> Electret microphone question

There are 26 messages in this thread.
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Author: MRW
Date: 13:18 15-01-07

Good morning everyone:

I have the following crude circuit on the breadboard:
http://img116.imageshack.us/my.php?image=micpreampbl4.jpg

The opamps are part of an LM6134 IC. Here is a link to its page:
http://www.national.com/pf/LM/LM6134.html

For my microphone, I am using this one that I got from Digikey:
http://catalog.digikey.com/scripts/partsearch.dll?Detail?name=423-1043-ND

Has anyone have any experience with microphones?

The mic is supposed to be omnidirectional, so I was thinking that I
should be able to hear its surroundings well. However, even by varying
the 10k pot to amplify the signal I really don't hear the surroundings
amplified that much. The microphone is a few inches away from an
oscilloscope with a loud fan. I was expecting to hear the fan from the
speakers. The only noticeable sound that I can hear if the tapping
sound of my finger near the breadboard.

Are there any tips to improve the sound pickup of the mic? Is my crude
circuit the cause of this? Or do I need to enclose the mic in a custom
enclosure?

I really don't know much about mic setups. All I know is that when my
friends call up and I'm using my bluetooth headset, they complain about
hearing the surroundings. I'd like to be able to duplicate that to some
extent.

Thanks!

Author: Tom Biasi
Date: 14:42 15-01-07

"MRW" <mr.whatever@gmail.com> wrote in message
news:1168885085.063760.40050@s34g2000cwa.googlegroups.com...
> Good morning everyone:
>
> I have the following crude circuit on the breadboard:
> http://img116.imageshack.us/my.php?image=micpreampbl4.jpg
>
> The opamps are part of an LM6134 IC. Here is a link to its page:
> http://www.national.com/pf/LM/LM6134.html
>
> For my microphone, I am using this one that I got from Digikey:
> http://catalog.digikey.com/scripts/partsearch.dll?Detail?name=423-1043-ND
>
>
> Has anyone have any experience with microphones?
>
> The mic is supposed to be omnidirectional, so I was thinking that I
> should be able to hear its surroundings well. However, even by varying
> the 10k pot to amplify the signal I really don't hear the surroundings
> amplified that much. The microphone is a few inches away from an
> oscilloscope with a loud fan. I was expecting to hear the fan from the
> speakers. The only noticeable sound that I can hear if the tapping
> sound of my finger near the breadboard.
>
> Are there any tips to improve the sound pickup of the mic? Is my crude
> circuit the cause of this? Or do I need to enclose the mic in a custom
> enclosure?
>
> I really don't know much about mic setups. All I know is that when my
> friends call up and I'm using my bluetooth headset, they complain about
> hearing the surroundings. I'd like to be able to duplicate that to some
> extent.
>
> Thanks!
>
How are you supplying power to the microphone?

Author: MRW
Date: 15:12 15-01-07

Tom Biasi wrote:
> How are you supplying power to the microphone?

Hi Tom,

The + terminal of the mic is connected to VCC via a series resistor.
That's the configuration they showed on the mic datasheet.

Author: Tom Biasi
Date: 15:52 15-01-07

"MRW" <mr.whatever@gmail.com> wrote in message
news:1168891953.836533.88670@m58g2000cwm.googlegroups.com...
> Tom Biasi wrote:
>> How are you supplying power to the microphone?
>
> Hi Tom,
>
> The + terminal of the mic is connected to VCC via a series resistor.
> That's the configuration they showed on the mic datasheet.
>
Did you actually measure the DC at the mic?
Tom

Author: MRW
Date: 16:36 15-01-07

Tom Biasi wrote:
> Did you actually measure the DC at the mic?

Yep, I used a multimeter and an oscilloscope to measure the voltage
levels.

Author: Phil Allison
Date: 21:10 15-01-07

"MRW" <mr.whatever@gmail.com> wrote in message
news:1168885085.063760.40050@s34g2000cwa.googlegroups.com...

** Groper Alert !

> I have the following crude circuit on the breadboard:
> http://img116.imageshack.us/my.php?image=micpreampbl4.jpg
>
> The opamps are part of an LM6134 IC. Here is a link to its page:
> http://www.national.com/pf/LM/LM6134.html
>
> For my microphone, I am using this one that I got from Digikey:
> http://catalog.digikey.com/scripts/partsearch.dll?Detail?name=423-1043-ND
>
>
> Has anyone have any experience with microphones?
>
> The mic is supposed to be omnidirectional, so I was thinking that I
> should be able to hear its surroundings well. However, even by varying
> the 10k pot to amplify the signal I really don't hear the surroundings
> amplified that much. The microphone is a few inches away from an
> oscilloscope with a loud fan. I was expecting to hear the fan from the
> speakers. The only noticeable sound that I can hear if the tapping
> sound of my finger near the breadboard.

** If you want to hear amplified room background noises - you MUST listen
to the mic via headphones, OR place the speakers in another room
acoustically isolated form the first.

There is NO WAY the crude PA system you have created will audibly amplify
any such sounds without breaking into a feedback howl.

....... Phil

Date: 03:32 16-01-07

MRW wrote:
> Good morning everyone:
>
> I have the following crude circuit on the breadboard:
> http://img116.imageshack.us/my.php?image=micpreampbl4.jpg
>
> The opamps are part of an LM6134 IC. Here is a link to its page:
> http://www.national.com/pf/LM/LM6134.html
>
> For my microphone, I am using this one that I got from Digikey:
> http://catalog.digikey.com/scripts/partsearch.dll?Detail?name=423-1043-ND
>
>
> Has anyone have any experience with microphones?
>
> The mic is supposed to be omnidirectional, so I was thinking that I
> should be able to hear its surroundings well. However, even by varying
> the 10k pot to amplify the signal I really don't hear the surroundings
> amplified that much. The microphone is a few inches away from an
> oscilloscope with a loud fan. I was expecting to hear the fan from the
> speakers. The only noticeable sound that I can hear if the tapping
> sound of my finger near the breadboard.
>
> Are there any tips to improve the sound pickup of the mic? Is my crude
> circuit the cause of this? Or do I need to enclose the mic in a custom
> enclosure?
>
> I really don't know much about mic setups. All I know is that when my
> friends call up and I'm using my bluetooth headset, they complain about
> hearing the surroundings. I'd like to be able to duplicate that to some
> extent.
>
> Thanks!

The opamps used by u is LM6134 IC. try replacing the with LM 324 with
is a universal purpose opamps.

Mike should be properly shielded wire, buy 1+1 wire with is available
in market ( one is normal and other one will be shielded ) now u will
able to hear any sound

Author: MRW
Date: 09:24 16-01-07

Hi Phil

Phil Allison wrote:
> ** Groper Alert !

Is it really wrong to be using Google Groups?

> ** If you want to hear amplified room background noises - you MUST listen
> to the mic via headphones, OR place the speakers in another room
> acoustically isolated form the first.
>
> There is NO WAY the crude PA system you have created will audibly amplify
> any such sounds without breaking into a feedback howl.

I actually wanted to hear feedback, but I never got any. At least the
feedback would tell me that it is picking up the sound from the
speakers.

Author: MRW
Date: 09:29 16-01-07

forestking_lion@hotmail.com wrote:
> Mike should be properly shielded wire, buy 1+1 wire with is available
> in market ( one is normal and other one will be shielded ) now u will
> able to hear any sound.

Thanks! Are there any other terms for 1+1 wire? It's just in case I
don't find it in my search.

Author: Phil Allison
Date: 09:46 16-01-07

"MRW" <mr.whatever@gmail.com> wrote in message
news:1168957450.093516.98420@38g2000cwa.googlegroups.com...
>
> Phil Allison wrote:

>> ** Groper Alert !
>
> Is it really wrong to be using Google Groups?

** You are not a part of usenet at all.

Just a fucking interloper.

....... Phil

Author: Phil Allison
Date: 09:46 16-01-07

"MRW" <mr.whatever@gmail.com> wrote in message
news:1168957792.423273.130330@a75g2000cwd.googlegroups.com...
> forestking_lion@hotmail.com wrote:
>> Mike should be properly shielded wire, buy 1+1 wire with is available
>> in market ( one is normal and other one will be shielded ) now u will
>> able to hear any sound.
>
> Thanks! Are there any other terms for 1+1 wire? It's just in case I
> don't find it in my search.

** LOL !!

Grope, grope, grope......

........ Phil

Author: MRW
Date: 10:38 16-01-07

Thanks, Phil!
http://members.iinet.com.au/~rutlidge/alanindex.html

Author: jfeng@my-deja.com
Date: 13:56 16-01-07

Try using a larger resistor to bias your microphone. I would try
something in the 100K-1Meg range.

Author: Ban
Date: 16:03 16-01-07

MRW wrote:
> Good morning everyone:
>
> I have the following crude circuit on the breadboard:
> http://img116.imageshack.us/my.php?image=micpreampbl4.jpg
>
> The opamps are part of an LM6134 IC. Here is a link to its page:
> http://www.national.com/pf/LM/LM6134.html
>
> For my microphone, I am using this one that I got from Digikey:
> http://catalog.digikey.com/scripts/partsearch.dll?Detail?name=423-1043-ND
>
>
> Has anyone have any experience with microphones?
>
> The mic is supposed to be omnidirectional, so I was thinking that I
> should be able to hear its surroundings well. However, even by varying
> the 10k pot to amplify the signal I really don't hear the surroundings
> amplified that much. The microphone is a few inches away from an
> oscilloscope with a loud fan. I was expecting to hear the fan from the
> speakers. The only noticeable sound that I can hear if the tapping
> sound of my finger near the breadboard.
>
> Are there any tips to improve the sound pickup of the mic? Is my crude
> circuit the cause of this? Or do I need to enclose the mic in a custom
> enclosure?
>
> I really don't know much about mic setups. All I know is that when my
> friends call up and I'm using my bluetooth headset, they complain
> about hearing the surroundings. I'd like to be able to duplicate that
> to some extent.
>
> Thanks!

You probably have blown your mike with overvoltage. It is rated for 2V
operation with that 2.2k, absolute max is 10V. You are operating it with
higher voltage I suppose, and blew the internal FET.
I would also filter a bit on that line, since any noise is amplified
together with the signal.
--
ciao Ban
Apricale, Italy

Author: MRW
Date: 18:56 16-01-07

jfeng@my-deja.com wrote:
> Try using a larger resistor to bias your microphone. I would try
> something in the 100K-1Meg range.

I used a 100k with the same results.

Author: MRW
Date: 19:07 16-01-07

Ban wrote:
> You probably have blown your mike with overvoltage. It is rated for 2V
> operation with that 2.2k, absolute max is 10V. You are operating it with
> higher voltage I suppose, and blew the internal FET.
> I would also filter a bit on that line, since any noise is amplified
> together with the signal.
> --
> ciao Ban
> Apricale, Italy

Hi Ban

The highest voltage setting that I've set my power supply is only 5V.
So I don't think that it's blown. What kind of filtering techniques can
I use? I already have some bypass caps close to the VCC pin of the IC.
I read about a guarding technique this website:
http://sound.westhost.com/dwopa.htm, but I don't know much about it,
yet.

Also, after looking at the microphone datasheet again and doing some
calculation, I got the following numbers:

Referring to 1kHz, at 30 dB re 20 uPa, the mic ideally outputs 4.74 uV.
At 80 dB re 20 uPa, 1.58 mV. These numbers are lower than my original
assumption. How would I handle signal levels like this properly besides
using low noise op amps?

Author: Michael Black
Date: 19:14 16-01-07

"MRW" (mr.whatever@gmail.com) writes:
> Hi Phil
>
> Phil Allison wrote:
>> ** Groper Alert !
>
> Is it really wrong to be using Google Groups?
>
>> ** If you want to hear amplified room background noises - you MUST listen
>> to the mic via headphones, OR place the speakers in another room
>> acoustically isolated form the first.
>>
>> There is NO WAY the crude PA system you have created will audibly amplify
>> any such sounds without breaking into a feedback howl.
>
>
> I actually wanted to hear feedback, but I never got any. At least the
> feedback would tell me that it is picking up the sound from the
> speakers.
>

So you take a step back, and take out the microphone. Inject an audio
signal where the microphone would be (make sure to use a coupling
capacitor). If you don't hear the tone, then you know something
else is wrong. If the point where the microphone is supposed
to go is high enough impedance, you should be able to touch the point
with a finger, and hear some hum.

If the injection doesn't work, then go to the output of the first
stage, and inject a signal there. If you hear something, then you know
the problem is ahead of that point. If you don't hear something, you
know the problem lies later in the circuit.

And so on.

Break things down into small sections, and make sure they work by
themselves. It's easier to figure out a problem the fewer components
you have to deal with.

Michael

Author: john jardine
Date: 19:53 16-01-07

Author: Michael Black
Date: 20:28 16-01-07

"jfeng@my-deja.com" (jfeng@my-deja.com) writes:
> Try using a larger resistor to bias your microphone. I would try
> something in the 100K-1Meg range.
>
You do realize there's nothing in there that's either going to be
damage, or requires such a high value resistor?

There's the actual electret element, and then there's an FET to buffer
the signal. The electret is really high output impedance, and the FET
doesn't load it down, but provides a lower output impedance.

Take one apart, and you'll likely find an actual garden variety FET.
That's what I found when I took one apart, I was actually surprised that
it was some recognizeable device and not some blob of epoxy.

You aren't biasing the microphone with that resistor. An electret
microphone is charged when manufactured and requires no external charge
or bias. The resistor is there to power the FET buffer.

HOw often do you see a circuit that runs off low voltage and yet
the voltage is run through such a large value resistor? You don't
see it much. You're likely to starve the circuit with such a high
value resistor and the low voltage.

And if you run up that resistor, you are back to a relatively high
impedance output from the microphone, even if the internal FET
buffer works okay with that large value resistor.

No, most resistors to power electret microphones are far lower,
no more than 10K and likely lower.

As for the other poster suggesting the microphone is blown, there is
virtually no reason that that could happen. There is no reason to
put in an FET that is so finicky that it won't run at reasonable voltages.

ANd of course, long before one should be wondering if the microphone
is bad (and it can easily be checked by powering it up and feeding it's
output to an existing amplifier through a coupling capacitor), the
circuit itself could be faulty, or something been's wired wrong.

Michael

Author: MRW
Date: 22:37 16-01-07

Michael Black wrote:
> So you take a step back, and take out the microphone. Inject an audio
> signal where the microphone would be (make sure to use a coupling
> capacitor). If you don't hear the tone, then you know something
> else is wrong. If the point where the microphone is supposed
> to go is high enough impedance, you should be able to touch the point
> with a finger, and hear some hum.
>
> If the injection doesn't work, then go to the output of the first
> stage, and inject a signal there. If you hear something, then you know
> the problem is ahead of that point. If you don't hear something, you
> know the problem lies later in the circuit.
>
> And so on.
>
> Break things down into small sections, and make sure they work by
> themselves. It's easier to figure out a problem the fewer components
> you have to deal with.

Hello Michael:

Yep, I did this, too. Even before I put the mic, I fed a 1kHz signal to
the input and got a nice 1kHz output waveform. I then added the
microphone and was able to hear the output if I tap or blow on the mic.
However, when I took a headphone connected to a walkman and held it
above the microphone, I was only able to hear a faint sound from
speaker even when I turned the speaker volume all the way up. I was
expecting to hear a louder output from the speaker since I can hear the
headphone output with my ears. I also had the gain of the amplifier
high. But then if I turn it all the way up, I get some feedback from
the speakers.

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