Audio filtering, experiment 29 of Make: Electronics part 2

Finally, after earlier setback, I’ve got the amplifier and 4-inch speaker working properly. I tried multiple setups today and managed to get rid of the distortion. The book dictates 9V, 33K resistance on audio input. This results in my case in a temperature of 90 degrees (194 fahrenheit). Which is uncomfortably high. I therefore decreased the voltage to 6V DC, increased the audio input resistance to 100K and added 10 ohm resistance to audio output. This gave a workable temperature of 60 degrees (140 fahrenheit). Because of these high temperature it is likely that the TEA2025B amplifiers that I bought for this experiment are part of a rejected batch.

After having solved this problem I added the coil, as a low pass filter, and the 11 uF bipolar capacitor as a high pass filter. Both filters work great with low frequencies on the low pass filter and high frequencies on the high pass filter. The coil is the same that I used in experiment 28 and the bipolar capacitor was made of two 22uF electrolytic capacitors.

Next I’ll fit the speaker in a shoebox and create a waveform with a 555 chip as an input for the audio amplifier (instead of the ipod).

Overview over the experiment with on the left the power supply, in the middle the ipod and on the right the breadboard.

A top-down view of the 4-inch speaker (top), breadboard and coil (bottom)

Close-up of the breadboard with on the left the TEA2025B amplifier. 

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