I'm working on an FPGA implementation of a retro '80s computer (see http://fpgabee.toptensoftware.com) and am trying to setup some 8-bit audio support. I'm using a sigma-delta DAC and a R/C low-pass filter.
What I currently have is a 3.3 V pin from the FPGA driving a circuit.
If I connect a pair of iPhone headphones I can hear the audio, it's sounds quite good although the volume is a little low.
What I'd like to do however is connect this to my PC for recording or to pass-through to my speakers. I tried connecting the above circuit directly to both line-in and microphone sockets on my sound card but the results were terrible. Nothing audible on the line-in, and very low volume and lots of noise on the microphone socket.
So I'm looking for is a simple circuit (I presume a amp of sorts) that will let me get a clean signal into the PC. I'm not talking about hi-fi quality stuff here - this is 8-bit audio driving a very simple dac.