Low power audio amplifier (lm386) help!!

Elitegamer83

Joined Jul 6, 2009
14
I'm building Mic for my iPod touch, It works okay. Problem is it can only pick up audio from a source that must be 6 inches or closer to be clearly herd.

I need some help with my schematic, I've looked up several lm386 amplifier circuits but really I'm new to electronics so I don'r necessarily understand all the terms and connections etc.

So would this circuit work for a x20 boost? or is it not wired correctly because I have a feeling it isn't. Thanks for your help in advance!

MikeML

Joined Oct 2, 2009
5,444
Is the mic an electret? If so, it needs to have a bias resistor, and a coupling capacitor. The amp is looks ok; is configured for a gain of 20. What is your speaker impedance?

Elitegamer83

Joined Jul 6, 2009
14
Is the mic an electret? If so, it needs to have a bias resistor, and a coupling capacitor. The amp is looks ok; is configured for a gain of 20. What is your speaker impedance?
Thank so much for the reply Mike!

Well like I said this was going to be an iPod mic so I was going to replace the speaker with a simple TRRS 1/8 stereo jack for the iPods mic IN. I didn't think was necessary to represent the connector in this schematic because I assumed it would be to the same effect.

Well I don't really know if it's an electret, I pulled it from a PC mic it has 2 pins positive and negative obviously.

Audioguru

Joined Dec 20, 2007
11,248
Look at Electret Microphone in Google Images to see if yours is the same.
Use a low noise opamp (TL071) instead of a noisy LM386 power amplifier IC.

Elitegamer83

Joined Jul 6, 2009
14
Well yes I suppose I do have an electret microphone then.

Are the pins the same on the TL-071? or would I need to change a lot of thing's in my schematic. Like I said I'm little new to electronics so this already seems complicated to me haha. It's a shame though Radio shack doesn't stock the part, I'm going to have to pay $4 shipping for an$0.80 part (Mouser.com)

Just curious, can I use a .047 Capacitor instead of one marked 0.05? also does the capacitor type matter?

This 'attachment' if you will is going to be portable but battery powered, is 6v enough to run the TL-071 properly?

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Audioguru

Joined Dec 20, 2007
11,248
The TL071 is an opamp.
The LM386 is a completely different power amp.
Look at the datasheet for the TL071 to see its pin numbers.
Here is the schematic of a TL071 as a mic preamp for an electret microphone. The 470k trimpot can be repaced by a resistor if you know how much gain you need.

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Elitegamer83

Joined Jul 6, 2009
14
Well that was a lot more complicated then I was really expecting or go for.

You have much more experience than me obviously, how well would a simple lm386 +20 gain circuit work with an incorporated microphone?

Would this work?

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Audioguru

Joined Dec 20, 2007
11,248
You need a gain of 200, not just 20 so add the capacitor beteen pin 1 and pin 8 as shown in the datasheet for the noisy (hiss) LM386 power amplifier.

Your electret mic needs a bias resistor that is powered from a filtered voltage.

What will the LM386 power amplifier be driving? A speaker or headphones? How will you prevent acoustical feedback howling?

Here is a noisy mic circuit:

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