Quote Originally Posted by CeeKayBass View Post
I use a headphone amp made by Vox called the 'amplug'.

The beauty of it is it plugs directly into my bass, and has an aux in which I run my iPhone into (you'll need a stereo mini cable to connect it - I use a Belkin retractable cable)

There are a number of different models for guitar depending on the sound you're after, and one bass model. Sound quality is pretty decent. Uses 2xAAA batteries which the website says will last about 15 hours (about right in my experience).

I'll second that. My Vox Bass Amplug plugs directly into my 1/4" upright bass jack. It has a 1/8" output for headphones and a 1/8" input for my iPhone and so I can play along with iReal Pro or the Amazing Slow-Downer loaded with play-alongs, or just with a favorite performance mp3. The sound is quite acceptable and the batteries last for many hours. Cheap fun and great practice. And since my travel upright is a solid body it's silent to my wife who is sleeping in our hotel room only a few feet away. Great for practicing outdoors on a park bench, even with noisy traffic around. The Amplug is about the size of my cell phone, so I can carry it, my cell phone, cable, collapsable headphones, and extra batteries in my pockets. And my bass breaks down or back up in about 8-10 minutes. Fits in my suitcase. Perfect play-along system, I think.