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May 6, 2010
about 2 years ago
Lex E I looked at the data sheet for the LM4990 prior to my original post and wondered about the direct coupling issue. You nailed the problem and adding the coupling cap appears to be the solution.
Loudspeakers do not tolerate DC for a number of reasons. I don’t know of any manufacturer that would recommend a DC component at the output of a power amp.
I believe the issue is directly related to how much quiescent current the LM4990 was supplying.
I need a few more of these for a project and I will be adding the series cap.
By the way, thanks for a product that makes it easier for me.
After more investigation,the problem is that there is about 2.25 VDC on the speaker pads. If I power the board up with no SD card there is only about 1mV on the amp output. So it is only when the amp is enabled.
I am having a problem with the audio power amp. I can play files using the stereo mini jack just fine. I configured the power amp on in the ini file and connected a speaker to the power amp output pads on the PCB. When I apply power to the board I hear two clicks from the speaker a few seconds apart. However, when I trigger a track I do not hear anything. Any Suggestions???
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