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hej all,
i'm trying to build a circuit with LOUD sound, but small form factor -- so i've been looking towards mobile phone speakers -- the ones that play music quite full-range and super loud. see here for example: http://httpwwwglobalsourcesmguisound.manufacturer.globalsources.com/si/6008820642893/pdtl/Micro-speaker/1007463385/Speaker.htm
i've been trying to power this little bugger with a normal op-amp circuit, but that doesn't seem to give it juice enough (audio is barely hearable) -- can someone help me out with a circuit?
or, perhaps, a powerful audio op amp?
best,
/j
« Last Edit: August 10, 2009, 04:02:11 am by jabstarr » Logged

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Try using a transistor to drive the speaker. Connect the speaker as if it is the relay coil in this circuit: http://www.arduino.cc/playground/uploads/Learning/relays.pdf

You don't need the diode and you may want to put a 100 ohm variable resistor in series with the speaker to experiment with the ideal level
« Last Edit: August 10, 2009, 04:04:20 am by mem » Logged

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i just tried setting this up, and the result is that the speaker goes to one extreme or the other, depending on the setting of the variable resistor...

[EDIT] for mem: took a pic of my setup... could you verify i am doing this right here? (green and white wire was only shorted when taking the picture, not when testing the circuit)
transistor is TIP120 -- audio signal is coming through the phono wire. 5V through red wire. [/EDIT]

this makes me think: will this also work with audio output from a DAC? - so not only on/off signals, but 12 bit waveforms running to the base of the transistor...?
thanks,
/j
« Last Edit: August 10, 2009, 05:11:50 am by jabstarr » Logged

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I don't think you connected the grounds, Dave.
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Don't forget that to get the best out of these speakers you'll need some form of baffle.
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Do you have the base and collector reversed? On a TIP120 the collector is in the center.

The collector should be connected to one side of the variable resistor. The base (the TIP120 pin opposite the emitter) should be connected through your 2k resistor or whatever to the arduino pin
« Last Edit: August 10, 2009, 06:09:16 am by mem » Logged

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mem, you're right, i connected the TIP120 wrong. thanks for the (TIP) tip.

i still get no sound though. or rather... i get a very weak signal, when connecting my signal from the DAC directly to the base, skipping the resistor.

could this be because i am running the audio from a DAC (generating a 12bit waveform around 2,5V, rather than clear ON/OFF signal), or should this be ok?
« Last Edit: August 10, 2009, 06:31:58 am by jabstarr » Logged

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What DAC?

Perhaps you should describe your complete setup and post your sketch.
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I drive speakers like these directly with a 2.5W class-D (300kHz) amplifier with no ill-effects.
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thanks guys!

@mem: it's a MCP4921 -- i have basically copied the schematic of the arduino pocket piano for my sound generation circuit: http://www.critterandguitari.com/home/store/pocketPiano/PocketPianoSchematic.gif
i have sound coming out of my output -- if i insert it to a mixer i get a nice signal, so i don't see any need for the sketch here. (its big and messy) --- but, again, basically its the same as the pocket piano project: http://www.critterandguitari.com/home/store/pocketPiano/HelloSineTone.zip

@AWOL: sounds perfect! can you give me a serial number of an amplifier like that?
« Last Edit: August 10, 2009, 10:15:22 am by jabstarr » Logged

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That clarifies things, you didn't mention the D/A in  your earlier posts so my comments assumed that you were driving the output from an arduino pin.

Any audio amp for driving a speaker should work.  You can make one using your TIP120 and a couple of 100k resistors using the information here:  http://sci-toys.com/scitoys/scitoys/computers/solderless/amplifier.html
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ah, sorry about that! i can see it was unclear...
best regards,
/j
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Sorry, where's the MCP4921??
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Quote
Try using a transistor to drive the speaker. Connect the speaker as if it is the relay coil in this circuit: http://www.arduino.cc/playground/uploads/Learning/relays.pdf

NO!  Whatever you do, DONT do this.  That will fry the loud speaker and the sound will be distorted.

Speakers must have zero DC bias or the coil travels to the end stop well out of the linear region.

You need an audio amp chip, there are many.
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