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### Topic: OP-AMP for SoundAmp in my proyect. (Read 1 time)previous topic - next topic

##### Feb 28, 2012, 05:02 pm
Hi guys,

this is my project
http://arduino.cc/playground/Main/AY38910

I wanted to add some op-amp to amplify the output sound of the chip Im using.

I found a very interesting diagram for a similar project (midibox) but for 12V at here  http://www.midibox.org/dokuwiki/doku.php?id=midibox_ay_3_8912_mixer

basically the use a IC with 3 op-amps and some pots to both ampligy the sound and control the volume which is exaclty what I want and need

my problem is since im noobish to electronics, do I need to change any of those resistors or condensator vaalues since the Arduino works on 5v and not 12v!??

If so some can guide me how can I determine (the process) of all those value? Ill be glad to work a bit and learn it for my self but im lost now

cheers and thank you!!

#1
##### Feb 28, 2012, 05:16 pm
LM386 is used for driving small speakers a lot.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### Grumpy_Mike

#2
##### Feb 28, 2012, 05:19 pm
Quote
do I need to change any of those resistors or condensator vaalues since the Arduino works on 5v and not 12v

Basically no.
The op amp is the important thing but it will work down to 3V so you should be fine.

#### mcleung

#3
##### Feb 28, 2012, 05:19 pm
If you supply your opamps with the +/- 12V, then everything should be fine.

The pot's select the gain you want (See negative feedback application )

When you set the pot to 0 Ohm, then it acts as a buffer (Gain = 1) and when the pot is at maximum, your gain would be 3.2 times your input. Depending on what your input is, you may need to use higher pots, but I think it should be fine.

#4
##### Feb 28, 2012, 05:20 pm
Hi!!

well Im not connecting this (the final project) to small speakr but normal speakers, even pre-amp concert speakers so dont know then if I should go with your recomendation??

another thing... I just noticed the +12V -12V, that probably means the other project uses a AC supply and not DC no?? I guess ill have to work a bit with the diagram on the bread board to make it work?

My only fear is to short my sound chips .

what will be the critearia to choose the propem op-amp ??

#5
##### Feb 28, 2012, 05:22 pm
No, +/- 12V DC.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### Grumpy_Mike

#6
##### Feb 28, 2012, 05:25 pm
You have to make a split supply from the single ended 5V supply.
Arduino Ground becomes -2.5V
Arduino +5V becomes +2.5v
then your amplifier ground is connected to the mid point of two 1K resistors as a potential divider going between the +5 and ground.
You should AC couple the audio inputs, that is connect then through capacitors.

#7
##### Feb 28, 2012, 05:28 pm
I see!

I think I got it Mike that was helpful.

Thanks to everybody for the quick reply

#### mcleung

#8
##### Feb 28, 2012, 05:33 pm
Just make sure the speakers you use are high input impedance, your LM324 can only drive a couple mA.

#### DVDdoug

#9
##### Feb 28, 2012, 07:38 pm
Quote
well Im not connecting this (the final project) to small speakr but normal speakers, even pre-amp concert speakers  so dont know then if I should go with your recomendation??
if I understand what you are doing, a mixer really isn't what you want.  And the regular op-amps don't have enough power (Watts & current) to drive a 4 or 8 ohm speaker.

A mixer is for mixing sounds... i.e. With a 3-input mixer, you could blend two guitars and a microphone (assuming they've been pre-amplified).

You can drive a preamp directly from the Arduino.  You just need a series capacitor (maybe 1uF) to knock-out the DC component.  A volume control (pot) would be a good idea too.   A series resistor (maybe 1K) wouldn't hurt either.   It will limit the current so that you don't wipe-out the Arduino if you accidently short-out the output (or if you accidently connect a speaker).

If you want to directly drive a speader, National Semiconductor makes lots of "Power Amplifier" chips.  Some of these can operate from 5V, and the circuit will usually be simpler than the mixer.

There are limits to how much power you can get from a given power supply:

With a 5V supply, you can theoretically get a little more than 1/3rd of a Watt into 8 Ohms.

With 12V, you can theoretically get a little more than 2W.

With +/- 12V, you get 4 times the power (8-9W).

With 4 Ohms, you double the power.

With a bridge* amplifier, you get 4 times the power.  (i.e. You should be able to get more than 2W with a 5V bridge amplifier into 4 ohms.)

In the real world, the amplifier can't put the full power supply voltage across the load and you get a little less power than you calculate.

* A bridge amplifier is a push-pull design with two "hot" wires going to the speaker, instead of one side being connected to ground.

#10
##### Feb 28, 2012, 08:15 pm
That sound more what I need... well I DO need a mixer, and a pre-amp so ill play around on both ideas and aalso check semiconductors IC cheers

#### DVDdoug

#11
##### Feb 28, 2012, 10:23 pm
Quote
That sound more what I need... well I DO need a mixer, and a pre-amp  so ill play around on both ideas and aalso check semiconductors IC  cheers
I don't want to discourage you fromlearning,  having fun, and building it  yourself.  But, you can buy a little mixer or amplifier fairly cheaply.

mixer \$23 USD.

Amplifier \$21 USD.

It can be fun to build stuff, but unless you want something unique that you can't buy, it's often cheaper to buy something already built.   The op-amps & electronic parts are cheap, but when you start adding a power supply, knobs & switches, and put it in a nice box, you usually end-up spending more.    Manufacturers can buy parts cheaper, they use low-cost labor (China, etc.), and there is very little per-unit labor on an assembly line...

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