Help needed in audio amplifier and dac.

Hi,

I want to build Portable audio player which can play wave files from
MMC (MultiMedia Card).The interfacing part of microcontroller and MMC
is done. I am stuck with playing part.The application I made which
reads from MMC and out it on microcontroller's PORT parallelly at 8khz
since my wave file is sampled at 8khz.

Here is the problem part. I want to build DAC and audio filter.Can
anyone suggest me any Ic which can be used as DAC and filter as well as
amplifier or any two of these. Currently I am using simple R-2R
ladder,RC filter and LM386 as amplifier.But in my case audio sound is
very noisy.Can someone help me?

Thanks and regards,
Gaurav Sarode.

Firstly consider your layout and power supply.

Do you have power supply capacitors close to the audio amp and the uC?

It is usually good to run to the power conenctions in a star topology, seperate ground and +v conenctions from the regulator to the microcontroller and the audio circuit.
If your power connection goes from the regulator to the audio amp and then to the micrcontroller then
the changes in current draw by the uC causes a varying voltage drop at the audio amp due to the resistance and inductance of the wire/track.

I'v found the lm386 to be a bit noisy. It may be better to use a chip such as the tda2822

If you get your player to work well I'd like to see the circuit. A recorded message unit is on my list of projects to do.

You can use a .wav file of silence (all zero samples) to check the noise floor of your hardware. You can connect the audio amp input to ground instead of the DAC output to get some idea of how much internal noise and power supply noise is getting to the loudspeaker.

Are you using 8 bit audio samples?

I'v worked on a device that used a device from the cirrus logic range of audio DAC's. It worked well.
There DAC's require a clock signal generated from a crystal. The audio samples are sent serially, you would need a resonably fast microcontroller to drive on directly, perhaps 5MIPS.


I'm sure you can find plenty of suitable DAC's if you look at semicondutor manufacturer's websites.