I'm extremely new to building circuits etc, as I come from the high-level software world, so please don't flame me .
I have a microphone and a speaker with plugs that connect to my computer's PCI sound card, and I want to build a small circuit to connect the two, separate of a PC, so that when sound goes into the microphone, it comes out from the speaker. I've read a bit about microphones and speakers and how they work, but I couldn't find much more information than that when searching, mostly because I'm not sure exactly what to search for. Can someone point me in the right direction?

 

You need a power amplifier to drive the speaker, a resistor to provide current to the microphone if it is an electret type and a battery or AC adapter for power.

Then if the microphone can hear the speaker they will howl due to acoustical feedback.

How loud do you want the speaker to be?

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Uncle $crooge

 

Thanks for your response.
I'm pretty sure I can find enough information to build the amplifier, but how can I figure out how much power I should provide to the microphone?
Also, how do I figure out if my microphone is electret or otherwise?

Thanks!

 

An amplifier IC is the easiest, probably the cheapest and works the best.
Many people start with the LM386 power amplifier IC. It provides about half a Watt of power to an 8 ohm speaker with a 9V supply.

Microphones don't have power provided to them. An electret mic needs 0.5mA of current, not power. The speaker gets the amplifier's power provided to it. The loudness of the speaker is caused by the amount of power from the amplifier. If the power from the amplifier is too high for the speaker then the speaker will break.

If it is slightly bigger than a pencil's eraser then it is electret. It will have two wires, one connected to its metal case which is ground in the circuit. The other wire gets a small positive DC current from a resistor and is its output.

Attached Images

LM386 with mic.PNG (13.0 KB, 43 views)

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Uncle $crooge

 

Wow, lots of info!
I am curious though, would it be a good idea to add a pre-amplifier circuit using something like the TL084 (by Texas Instruments) before the LM386 shown in your circuit? Or would that make much of a difference?

Edit- By the way, please forgive me for the delayed replies; I googled extensively before my responses .

 

yes, you can do this to increase the gain if necessary. You may want to breadboard the circuit above to see if it is adequate before adding the TL084.

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"Everything that is done in the world is done by hope." -Martin Luther
"There are two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."-Albert Einstein

 

I didn't feel it was necessary to start a new thread for this question-
I've been trying to figure out where I can get a DIP version of the TL084 chip by Texas Instruments (mentioned earlier in thread), but everywhere I look there are 8 to 18 week lead times. Does anyone know where (and if) I can get 1-5 of these chips within a reasonable amount of time (a few days to one or two weeks)?

 

Where are you located? It's always good to fill in the location field in your profile.

The 386 design Audioguru shows should be fine without preamplification as the 386 is set up to have a gain of 200 (increased from 20 by the 10uF cap between pins 8 and 1).

Here is the datasheet for the part. Although the half watt or so of power will produce a respectable sound level (a little higher than talking level without much distortion and with a reasonably efficient speaker) you may want more power depending on your application.

http://www.national.com/pf/LM/LM386.html

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Angry!? I'm absolutely electrolytic!

Will have to make do with myspace now I guess...

 

Texas
Yes, I saw the datasheet earlier, but there is one question I forgot to ask- between the LM386N-1 and N-3, the only difference seems to be the output power (Pout) under the Electrical Characteristics section. What specifically do those numbers mean? Does it mean the N-3 will amplify louder because it has more output power?
I don't really need more power, but I want more just 'cause . Its the Texan way.

Also, silly me, I forgot to check froogle for the TL084...

 

Yep, the N-1, N-3 etc just have different power outputs. The N-3 would go louder with less distortion than lower number models.

Not sure if you have tried this site yet:

http://www.digikey.com/scripts/DkSea...181907&Site=US

Also, the TL084 is a quad op-amp. The 082 or 081 are dual and single respectively.

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Angry!? I'm absolutely electrolytic!

Will have to make do with myspace now I guess...

 

Well it wasn't the LM386 with which I had a problem with delivery time... National is nice and gives us free 24 hour samples, maximum of 5 units per sample and 5 samples per week, makes me all fuzzy and warm inside. :cool:
It was the TI TL084 that I was questioning, as I can't tell if the Lead Time applies to only large orders or samples as well, and the lead times were all from 4-24 weeks. I just didn't know so many companies distributed this stuff until I froogled it.
Once I get all the parts together I might take some pictures and post them here, just for the heck of it.

 

The TL084 is a useful part to have, but shouldn't be totally needed in this application (unless you need very high sensitivity). I edited my previous post btw after realising it was the 084 you wanted. Still not sure if there is a lead on it though.

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Angry!? I'm absolutely electrolytic!

Will have to make do with myspace now I guess...

 

You don't need a quad op amp (TL084). Try finding TL071 or TL081 (single), or TL072 or TL082 (dual).

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Ron

 

The LM386 schematic I attached has a voltage gain of 200 which is plenty of gain. So an additional preamp will not be required.

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Uncle $crooge

 

Am I right in thinking that a quad just acts like 4 singles, but in one chip? That's what it looks like from the documentation.
Am I also right in thinking that if I run the output of the first into the input of the second etc, that I could increase the voltage even more? Not that I need it, I just think it would be interesting to try.

Definately! One thing I can't stop myself from asking is, what the heck does all that stuff do (the components in the circuit you posted)? More specifically as an example, why are there so many capacitors (I counted 6) and what exactly do they do in this circuit? I have no idea. I guess its not important to know the theory to build a circuit (at least from someone else's design), but it would be nice if I could understand it better. Is there a good book I can buy (or something) that explains these kinds of things? Sorry if I come off as rude (or extremely newbish, which I am), I just really want to get into this kind of thing, and I don't know much about it.