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Topic: Simple audio amplifier  (Read 636 times) previous topic - next topic

Rightthen

Is there any way to make a really simple audio amplifier. I just want something that I can say something into the mic and it plays out a speaker. If anyone has advice or has a picture of how I should wire it that would be great!

PieterP

With an Arduino? No. An audio amplifier is an analog device.

Rightthen

Is there something similar to it though?

DVDdoug

#3
Jun 30, 2018, 07:47 pm Last Edit: Jun 30, 2018, 08:04 pm by DVDdoug
It's called a PA system    (Public Address System).   ;) 
SOME BACKGROUND - Typically, you have a preamp stage with a gain of about 100 to bring the millivolt microphone signal up to line level (about 1V).    Then a power amplifier with a gain of 10 or 20, and more current & power capability to drive the speaker.    ...With a volume control in-between.

The audio output from your TV or CD/DVD player is line-level.   You plug that into your stereo receiver which contains a power amplifier.    "Powered" computer speaker also take a line-level

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input.    A headphone output is about the same voltage a line-level signal (with more current capability to drive headphones) so you can plug the headphone-output from your laptop or cell phone into your stereo system, or into powered computer speakers, etc.

A power amplifier can put-out less than 1 Watt or 1000 Watts or more.     A home stereo/home theater system is usually around 100W per channel, but most of the time it's putting-out less than 10W.    The speaker in your TV is probably driven by a 5-10W amplifier.   A "standard" factory car stereo might put-out 10-20W and a "loud" aftermarket car stereo can be hundreds of Watts or more.

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The LM386 is a small (low-power) power amplifier chip that can drive a speaker.    It can be configured with a gain up to 200 so you might be able to get-by without a preamp, depending on how much signal you're getting out of the microphone.   That depends on the sensitivity of the mic and the loudness of the sound that's hitting the mic.    The signal from the mic is highly-unpredictable and that's why preamps normally have a volume/gain control and plenty of gain.

Texas Instruments makes a wide variety of amplifier chips. 

Almost any op-amp can be used as a preamp.   But, most op-amp circuits require bipolar power supplies.

Electret condenser "computer microphones" require 5V power which is normally supplied by the soundcard.   A "stage/performance" electret microphone usually has an internal battery.    Dynamic mics (like the famous Shure SM57/58) don't require power.    Studio condenser mics require 48V phantom power.

Stage & studio mics use "balanced" (3-wire) XLR connection.   Good quality microphone preamps have balanced (differential) inputs.    Regular computer mics and soundcards unbalanced (one signal wire and a ground).

Here is the schematic for the SparkFun Microphone Breakout board.    The preamp runs from a single 5V supply and it supplies power for the electret mic. (The SparkFun board has a 2.5VDC biased output, which you need for the Arduino but for connection to a power amplifier you need a capacitor in series with the output to block the DC.)

Rightthen

That's alot of info. I may have a LM386 chip (doubt it though) but I know I have a dynamic mic. Thanks for the info, I may get this done sooner than I thought.

MarkT

#5
Jul 01, 2018, 10:50 pm Last Edit: Jul 01, 2018, 11:08 pm by MarkT
But, most op-amp circuits require bipolar power supplies.
Just setup a virtual ground using another opamp, almost any opamp circuit can be made single-supply.

For microphone level inputs a low-noise opamp is needed, something like the NE5532, but probably
a rail-to-rail low voltage modern opamp would be better - but pick a low noise one.

BTW that Sparkfun microphone breakout board circuit was clearly not designed by anyone
familiar with low-noise amplifier circuits, as it has a 10k resistor in series with the microphone
signal, a very basic error as that resistor will generate far more noise than anything else in the
circuit.

The correct circuit for an opamp microphone amplifier is a non-inverting configuration, using
something like 33k / 330 divider from output to the inverting input (the 330 ohm resistor
will generate little noise).   In the non-inverting configuration the signal path only has to
drive the opamp input stage which will involve the minimum of loading and no extra
resistance in series with the dynamic microphone's own low-impedance winding.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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