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### Topic: Simple speaker amplifier circuit? (Read 6022 times)previous topic - next topic

#### theoneandonlymc

##### May 23, 2011, 11:08 pm
I'm looking for a simple circuit to get the most noise I can out of two 2W (max. 3W) speakers attached to an UNO, without blowing them up!
The speakers I'm using are http://www.visaton.com/en/chassis_zubehoer/wasserfest/k50wp_8.html

Sound for both will be generated of the same pin on the UNO, and it's just simple pulsed tones at two different frequencies, so sound quality isn't too big a concern.

Having had a search of the forum, I've found this diagram -

And is the simplest circuit I've found so far, however I'd like to drive it with more than 5V, but I'm not entirely sure how to calculate the necessary resistor sizes (is it just a simple case of using the resistance/power rating along with the usual equations?)

This project will be getting powered from a 12V car battery, but to keep power consistent for the speakers, I'll probably add a 9V regulator just for them.

Is this circuit the simplest way to get reliable sound, or should I be looking at something different?

#1
##### May 23, 2011, 11:23 pm
Do a search for MOSFET Amplifier, I have one posted that runs from 12V and is quite loud thru a 4 ohm speaker from www.mpja.com
A logic level N-channel MOSFET, 220uF cap, couple of 68 ohm resistors are all you need. I have the resistors wired with a switch so I can have them in series or in parallel to act as a simple hi/lo volume switch. The 220uF is definitely needed to let the AC out to the speaker.
If you put in the 9V regular you will give up power output: Pmax = V^2/R, so 9V vs 12V makes big difference.
But you will keep car alternator noise out - guess its a tradeoff.
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.

#### theoneandonlymc

#2
##### May 23, 2011, 11:32 pm
Thanks for that.
I shall go do some searching.

The reason I was thinking of using a 9V regulator, was because the battery won't be getting any charge while in use, the voltage will gradually drop, along with the speaker volume.

However, thinking about it, other than a bit noise (there's also 4 electromagnets being switched by the UNO at the same time), it's probably more hassle than it's worth to add a seperate regulator.
I'm needing to get this project in a useable state for the weekend, so I can always add some noise suppresion at a later date if it's going to be an issue.

#3
##### May 24, 2011, 02:04 am
Here's the one I use

Was based on this design, skipping the biasing as we only turn it full on/full off with the arduino digital output
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.

#### theoneandonlymc

#4
##### May 24, 2011, 01:39 pm
Thanks for that, but do you have any specs for the MOSFET?
Google doesn't show up any results for the IRF37072...

#5
##### May 25, 2011, 05:36 am
IRF3707 zee
International Rectifier
Turns out that particular part went obsolete after I bought a tube of 10 (and not long after - like, by the first time I recommended them here!)
This one looks like a good replacement
http://www.irf.com/product-info/datasheets/data/irlb8748pbf.pdf
Not marketed as a Logic level Mosfet, but Rds with Vgs  of 4.5V is still really low, 0.0055 ohm
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.

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