|Casio SA76 44-Key Mini Keyboard|
-37 to 49 keys (less than 30" wide)
-Ability to plug in headphones
-Wall socket / AC-adapter powered (not USB)
Surprisingly, in this world of Amazon and eBay, I could only find two digital pianos currently available that met all of these criteria - one of them at $399 and one of them at $50. Every other digital keyboard was either 61-keys or larger (I already have that) or some kind of computer-reliant MIDI/USB device (not interested). I just need it to make a piano sound.
The $399 option was the Yamaha Reface series, particularly the Reface CP model. I liked the fact that the Reface CP was a professional quality instrument with simple, easy to use knobs. What I didn't like was the cost and the bad reviews regarding its built-in speakers. If I had chosen the Reface it seemed like I may also have needed to purchase some kind of external speaker or amp to use with it. I also didn't love the fact that it was only 37 keys, but I did like how that made it super-compact. The vintage Rhodes, Clavinet and Wurlitzer sounds it contains weren't a big deal to me one way or another. It was hard for me to tell who these Yamaha Reface mini keyboards were intended for. Not for me, I guess.
So I chose the $50 keyboard, which is the Casio SA76. Actually, it was more like $60 because the AC adapter that you need to plug it into the wall is an additional cost. You could just use six "AA" batteries, but I wanted to be able to plug it in. This instrument is definitely intended to be more of a child's toy, but it actually suits my needs quite nicely. You get what you pay for so it's not anything all that incredible, but I like having it handy for working out things by ear and for reinforcing stuff that I am learning on a more full-size keyboard.
The SA76 has 44 mini-sized keys, but I actually don't mind this too much. That is seven more keys than are on the Yamaha Reface, which are also mini-sized. (As a stringed instrument player, I go back and forth between the tenor banjo's 21-inch scale and the mandolin's 14-inch scale without much trouble, so I'm not too worried about this when it comes to the piano keyboard).
I've hardly used any of the features of the SA76 thus far, and don't really intend to do much of that. When it arrived I simply turned it on and started playing. Usually I just scroll through the sounds it can make and find one within the first 10 that seems suitable to me at that moment. If it just had one sound and that was a sampled "piano" sound it would be fine with me. That's all I'm looking for.
So the verdict is I'm glad I found something. It's surprising that there aren't any other keyboards like this besides these two. If you know of any other digital pianos that meet all of the requirements above PLEASE leave a comment! What I really would like is a smaller version of the Yamaha P-45, with 44 or 49 full-sized keys instead of 88. That would still be compact enough but would be more playable. Or maybe if the Reface model cut its price in half to $200 and improved its built-in speakers, then it would be the perfect mini keyboard. For now I'm happy with the Casio SA76.