I have an old Yamaha SY22 synth which I want to use as a MIDI keyboard. The problem is anything I play is too quiet?! If I use any other controller to record the midi data the sound is a lot stronger.

Velocity doesn't seem to be the issue because when I play I can get up to 127 velocity - yet anything played through it ends up giving me quieter midi data. I'm STUMPED!

Does anyone have any suggestions or ideas?

Gavin

Have you checked to see if there is any controller data being recorded along with what you play? Volume or expression for instance?

Velocity doesn't seem to be the issue because when I play I can get up to 127 velocity

 
I think you're right.  I just had a look at the manual to make sure it wasn't one of those early, V=64 non-velocity synths.  It isn't.

- yet anything played through it ends up giving me quieter midi data.

This might be something to look into.  The MIDI Implementation Chart indicates that CC7 (volume) is not received unless "control change sw is on".  The same goes for mod wheel (CC1), CC16 and 17 (for the vector joystick X & Y), and sustain (CC64).  That might be a way to trace it back.