I have got audio playing from a .WAV file on a microSD card via a ATTiny85, when I amplify the output I'm getting a very audible buzzing/interference over the top of my audio file. When I amplify other inputs with the same amplifier circuit this interference/buzzing is not present, so it's defiantly being caused by something in my audio circuit. Is this to be expected or what would be causing this/how can it be reduced or eliminated?
Below is my circuit diagram. The setup is replacing an ISD17240PY hence its interfaced to a 28pin socket so I can just plug it in to my existing circuit board.
I have now built up the circuit bare bones on strip board, using a SD card and the ATTiny85, an electrolytic capacitor across the supply and a good stable power supply to provide 3.3v, then a capacitor on the audio output directly to a little speaker. When the audio signal is quiet there is an audible buzzing/interference, and when amplified it is very loud all the time. Could this be to do with the internal clock of the ATTiny85?
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