This one comes from the slim volume, Simple Test Equipment for the QRPer. Reviewed on Soldersmoke, it has a number of excellent projects for simple test equipment. The above schematic is linked from Linear Technology's website. They make the LTC1799, the heart of this very simple circuit. The chips page is here. It can go from 1kHz to 33MHz. It's a little fast, but it may have some interesting audio applications as well. As usual, Linear offers free samples. I haven't sampled from them before, so I can't say for certain how good they are at it. Give them a shot! Remember, don't be shy about sampling. The cost of these chips to the company is very small, and for them is a very valuable promotional tool. If you build something, and make a kit out of it, they can sell hundreds of these chips.