I built one years ago with a cassette player and amp that works like a dream.
Now I am putting one together with an amp, bluetooth receiver which I intend to play the calls from my Iphone to the blue tooth box. I have an app on my Iphone and can also play MP3s.
I built one a few years ago using an MP3 player, a mini amp, and a powerhorn that I found on Varmint Al's website. It works pretty well, all I need is better quality sounds than what I'm using.
I was kinda hoping I could download some good MP3s. I had found a few on one website, but they really weren't that good. I would even pay to download some. I guess the best thing to do is order CDs and get them off or covert them. I do have an app on my phone called iHunt which has some crow calls on it. They are pretty short ones but can be repeated. Any suggestions?