Josh Koffman wrote: > here:http://www.datasheetarchive.com/pdf-datasheets/Datasheets-19/DSA-363980.html > ). The output of the DAC is fed into a TI TPA2000d2 Class D Amplifier > (datasheet here: http://focus.ti.com/lit/ds/symlink/tpa2000d2.pdf ). > > This seems promising to me since it means there are actual analog low > level signals on the board I can tap into and inject a signal into the > final amp (ie it isn't all done inside one large chip). The question > is how to do it. My current thought is to take the audio from my input > jack, feed it through a 0.1uF cap, then perhaps a 1K resistor, then > into the audio input of the TPA2000d2. Thoughts on that? Analog isn't > my strong suit. Also, the TPA seems to want an audio in positive and > negative. In this case would I just tie to the L and R negatives > together? Caps and resistors needed on those too? Just my .02 Yes I like your idea if you also use an identical value resistor inserted into the main audio path as well. Maybe there is one already there. 0.1 uF is a little small for a cap value if you are using 1K ohm, the low frequencies won't get through. But see if there's a resistor already between the DAC and this amp chip, and if so you can use the same value. But use 10uF for your cap value if you use 1K ohm, then your -3db point is 16 Hz. I bet the inputs are not being used in a differential fashion, except perhaps for ground loop suppression. So you could probably scope it out while it's running and see if there's audio on both + and - signal inputs and inject yours into the one that has signal. I bet this could be really easy. Adding an opamp is likely to make it noisier and less stable. Cheerful regards, Bob -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist