Hi everyone,
A quick post here for now. I teach piano and singing and your son will definitely benefit and improve with a weighted touch keyboard. At least 76 but preferably 88.(and most importantly a teacher who will relate to your son and the music he likes to play)
The lighter keyboards are a way for parents to see if their kids are going to keep on with piano lessons without having to outlay a lot but they really don't help with technique etc and they run out of keys really fast. But if you want a good keyboard that will last it's going to cost.
I bought myself a Roland 300GX digital piano on sale a couple of years ago for $2000.(it was $3000!).It's 88 keys,weighted but needs speakers.(Roland Cubes).It has USB connection, MIDI in and out and a built in MIDI file and wav player.
Best of all I can load my BIAB backing tracks on a USB stick for myself or piano students to play along with and have BIAB backing tracks for my singers to sing along with. I love it!
I'd check out music stores for sales or look out for a good used keyboard. Yamaha, Roland, Casio, they're getting better all the time. I have also heard good things about the Privia but haven't checked one out for myself. (I'm just an old Roland person from the D50 days).
All the best of luck!
