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How to pick simple microphone for breadboard and LM386

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mbird

New Member
Hi --

I wanted to buy some parts to experiment on my breadboard. One thing I wanted to play with is LM386 and add microphone and little speaker.

What microphone should I buy? I want one that will just plug into the breadboard. I see DigiKey, etc. have lots of them but what I don't understand is what they mean by "Voltage Rating." Why is their a voltage rating if I don't apply any voltage to the microphone (it is behind a cap and goes into the LM386 or into base of transistor amp stage).

Is some basic one like this one fine for just experimenting?

Thank you!
 

colin55

Well-Known Member
You will need to connect the wire that goes to the case (outside) of the microphone to the 0v of your project. Connect a 22n (223) ceramic capacitor from the other wire to the input of the amplifier chip. Now connect a 22k to 47k resistor from the same wire on the microphone to the positive supply of your project.
 

audioguru

Well-Known Member
Most Helpful Member
You will need to connect the wire that goes to the case (outside) of the microphone to the 0v of your project. Connect a 22n (223) ceramic capacitor from the other wire to the input of the amplifier chip. Now connect a 22k to 47k resistor from the same wire on the microphone to the positive supply of your project.
Never use a ceramic capacitor to couple low level audio:
1) It is microphonic (the capacitor becomes a microphone).
2) Its value changes with voltage which creates low frequency distortion.
Use a film capacitor instead.
Use a 10k resistor since most electret mics need 0.5mA.

If the mic can hear the speaker then you will have acoustical feedback howling.
 

colin55

Well-Known Member
I have sold over 100,000 kits using 22n and 47k for 3v supply. Any lower resistance and the microphone is overloaded - unless it is a junk electret mic.

You obviolsy don't know what you are talking about.
 

audioguru

Well-Known Member
Most Helpful Member
I have sold over 100,000 kits using 22n and 47k for 3v supply. Any lower resistance and the microphone is overloaded - unless it is a junk electret mic.

You obviolsy don't know what you are talking about.
Everybody (except you) use film capacitors to couple a mic to a preamp.
Ceramic capacitors are used for supply bypass, not for coupling audio.

Your capacitor value is so low that the sound will be without low frequencies like a telephone.

Most electret mics operate at 500uA. Yours has less than 1/10th.

I don't think I will ever buy your kit.
 

flat5

Member
When I bought a Sanyo minidisk ? years ago I did some tests with very inexpensive electret mic buttons to check noise level and decided on 6.8k with 9v source. Most articles suggest 10k.
Perhaps I just had a good resistor. I could hear the difference. The output level and overload sensitivity were about the same with 6.8k and 10k.
 
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audioguru

Well-Known Member
Most Helpful Member
An electret mic works fine with a 10k resistor feeding it from a decoupled 9V supply.
The impedance of the FET in the mic is about 3.3k ohms so 10k does not load it down too much.
 

mbird

New Member
Hi --

I found two inexpensive mics on DigiKey:
-Electret Condenser, 4.5-10V, 500uA, see link.
-Electret Condenser, 2V, 500uA, see link.

Just to confirm...
1.) Are the above mics OK for experiment with LM386
2.) What size capacitor should I use to couple the mic to the LM386?
3.) If I use speaker jack from computer or little radio as input to LM386 instead of mic do I need capacitor to couple to LM386?
4.) If I use output of simple one-transistor CE amp I made what size capacitor should I use?

I am just experimenting hobby mode so cheap mic and cheap 250mW speaker is OK for me.

Thank you
 
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AllVol

New Member
Hi --

I found two inexpensive mics on DigiKey:
-Electret Condenser, 4.5-10V, 500uA, see link.
-Electret Condenser, 2V, 500uA, see link.
Of the two, I would go with the first one.

Attached is a device I built before I got professional hearing aids. It uses
the LM386 and an identical Electret mike. It worked so well I intended to put it in an Altoids can to carry in my shirt pocket, but the real aids came along before I completed the project.

It really does work well, with ear buds. Use with a speaker is pretty much hit and miss and depends on the caps you use, I found.

Don't be mad, but I won't answer your questions. That's what experimenting is for. LOL.

Good luck
 

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Mikebits

Well-Known Member
I have sold over 100,000 kits using 22n and 47k for 3v supply. Any lower resistance and the microphone is overloaded - unless it is a junk electret mic.

You obviolsy don't know what you are talking about.
I have seen some of the projects on your website, like your claimed 30W + 30W @ 12v amplifier that uses a part max rated at 20W @ 14.4v
 

colin55

Well-Known Member
There must be something seriously wrong with you.

The article is not on my website.

In fact I did not add the link. My site allows readers to add links. This was added by a reader.

My site contains a link to the author’s website, as follows:

This project can be seen on the following website:
Welcom

xxhttp://www.e-monsite.com/aply123/rubrique-1049505.html
 
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Mikebits

Well-Known Member
There must be something seriously wrong with you.

The article is not on my website.

In fact I did not add the link. My site allows readers to add links. This was added by a reader.

My site contains a link to the author’s website, as follows:

This project can be seen on the following website:
Welcom

xxhttp://www.e-monsite.com/aply123/rubrique-1049505.html
Nothing wrong with me. I do not plagiarize other peoples works, you however do. There are no indications on your website that you are infact borrowing works made by others. I do not see any written disclaimers or the like that your posted projects are links from other websites.

Considering the fact that you do plagerize, you should at least check the validity of the circuit/circuits that you copy.

I searched for awhile, I do not see a link where I might add to your long collection of bogus circuits. Please explain how I might add a link...
 

colin55

Well-Known Member
Firstly I did not say the circuit was mine. The circuit is in FRENCH.
My site contained a link to the author. In no way can this be considered plagiarism. To start with, you can comment on anyone’s work up to 10%. Secondly I did not provide any kits or parts for the circuit and made no comments about the circuit at all.
You really need an education. When you get a site with 1.5Gig of traffic per day, I will visit your site.
 
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Mikebits

Well-Known Member
Firstly I did not say the circuit was mine. The circuit is in FRENCH.
My site contained a link to the author. In no way can this be considered plagiarism. To start with, you can comment on anyone’s work up to 10%. Secondly I did not provide any kits or parts for the circuit and made no comments about the circuit at all.
You really need an education. When you get a site with 1.5Gig of traffic per day, I will visit your site.
By the way your material is presented, it is implied by you that the material is yours. Nowhere in the presented material do you offer credits for the original designer. You do say;

This project can be seen on the following website:
This in no way indicates that you are giving credit to the originator.

I would not be proud of a large traffic website that was based on fraud and deception. Sleep well ...
 

colin55

Well-Known Member
Thank you for promoting my site again. Your cheque for $50.00 is in the mail.
All of the projects on my site have been stolen from other sites and it’s just a matter or looking and seeing where they have been stolen from.
Your critique reminds me of the local Bikini Car Wash. It wasn’t doing so well until the local minister complained about “disgusting” young girls washing cars. The local paper had the address and photos. The car wash is now doing fantastic.
The minister complained again after 3 months and the business is still roaring. Again, I thank you.
 

Mikebits

Well-Known Member
I have to admit, that was good. Ya got me there.
 

Mikebits

Well-Known Member
But advertising aside, I stand by what I say... so there. :p
 

mbird

New Member
And now after a short intermission back to the original question... :)

I want to experiment with LM386. I choose two possible mics below that are available and inexpensive for breadboard experiment:
-Electret Condenser, 4.5-10V, 500uA, see link.
-Electret Condenser, 2V, 500uA, see link.

I have read different opinion on how to connect microphone via capacitor:
I am not sure how you go about determining the correct capacitor size to connect the mic to the LM386. I understand the reason for the cap but I don't understand how to pick the correct value. I have read 0.022uF but I would like to confirm and also understand how/why that is the correct cap.

Thanks!
 

Sceadwian

Banned
I looked at a couple schematics and they use anywhere from 2-10u electrolytics. I'd say 10u is a decent value for general performance. I'm not sure why colin recommend ceramics, every schematic I've found for electret pre-amps use electrolytics. Even the cheapest electret mic actually has pretty solid audio perforamnce if you use good parts around it. They are relatively noisey though, so you have to watch how much yuo amplifiy it.
 
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audioguru

Well-Known Member
Most Helpful Member
I looked at a couple schematics and they use anywhere from 2-10u electrolytics. I'd say 10u is a decent value for general performance. I'm not sure why colin recommend ceramics, every schematic I've found for electret pre-amps use electrolytics. Even the cheapest electret mic actually has pretty solid audio perforamnce if you use good parts around it. They are relatively noisey though, so you have to watch how much yuo amplifiy it.
The input resistance of the LM386 is 50k ohms and if a 100k volume control is used, the input impedance is 33.3k ohms (or more if the volume control is turned down).
A 10uF coupling capacitor will have a response down to 0.48Hz (or lower if the volume control is turned down). Too low.
I would select a 220nF film capacitor for a response down to 22Hz.

Colin's 0.022uF ceramic capacitor will produce a response down to 220Hz (or higher if the tolerance is poor) almost like a telephone.

If the mic can hear the speaker then you will have acoustical feedback howling.

Make it like this:
 

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