I have a design that uses an ATXMega32E5 for two audio sources. In one case, a timer output square wave (3.3v logic) goes through a low-pass filter to make beeps, and in the other case, a DAC channel outputs 8 kHz audio samples (0-3.3v). Each goes into a 20k pot, the output of which goes into an LM4871, and into an 8Ω speaker.
The audio sounds fine, but the levels are way too low - like hold the speaker next to your ear.
I tried cranking up the LM4871 gain a little, but you're not really supposed to do that, and 3 dB of gain from the reference design didn't really make much of a difference I could hear.
I'm thinking the correct thing to do is stick an op amp (inverting configuration with half-vcc virtual ground) gain stage in.
Audio isn't really my strong suit. Can someone look over the proposed design and tell me what's wrong with it? :)
The original circuit just connects the R8/R13 output directly to C23. Everything between those two points is the addition I'm thinking of.
Note that during the test, AUDEN is high - with AUDEN low, there's no audio at all (which is the whole point of that line).
P.s. The differential output on the speaker leads (with the speaker attached) is around 2v P-P. Is it perhaps just that this speaker sucks?
