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Topic: DAC help (Read 787 times) previous topic - next topic

Hey everyone, I just bought a MCP4725 DAC from sparkfun online:

http://www.sparkfun.com/products/8736

This DAC has 12 bits of resolution from 0V to 5V

Now that I attached it to some speakers and made it play a simple square wave, its only making a scratching sound, like when you hook up a battery to some speakers. I was wondering if I absolutely need a negative current to work the speakers. And if so, how would I do this?

Thanks in advance for your help

Grumpy_Mike

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I was wondering if I absolutely need a negative current to work the speakers

No it will work off a single supply.
However, you can't just connect it up to a speaker because it takes much more current than the chip can supply, you will need an amplifier before the speaker. I hope you have not blown up the D/A chip by trying to draw too much current from it.

Then how can I generate a negative voltage? Is this AC coupling?

Grumpy_Mike

Why do you want to generate a negative voltage?

retrolefty

First you need to run the output of the DAC through a series capacitor, 1 ufd should cover low enough tones, that will remove the DC bias and give you a true AC voltage referenced to ground. Second your DAC does not have a low enough output impedenance (source current drive) to directly drive anything but a very small speaker, it really should wire to a audio preamp/amp device sized for the speaker output wattage you require.

Lefty


I am aware that the DAC is not powerful enough to drive large speakers ( I am currently using old laptop speakers ). And thanks lefty, i'll definitively do the capacitor thing.

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Why do you want to generate a negative voltage?


Because to drive speakers you need a negative voltage, Am I wrong?

Thank you for your help


Grumpy_Mike

Yes you are wrong. Using a capacitor for coupling removes the DC bias and makes your varying DC signal into an AC one. That is also what an amplifier will do for you like I said on my first reply.

Thank you all for your help

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