It sounds like the heavy key action on your Yamaha DGX-650 is definitely contributing to your difficulty with the Minute Waltz, especially for those rapid left-hand chord changes. Unfortunately, digital pianos generally have fixed key actions, and there isn’t a straightforward way to mechanically lighten the key action without significant modification or replacing the instrument.
Here are a few things you can try to mitigate the issue:
Adjust Your Playing Technique: You could experiment with adjusting your hand and wrist position to help with the weight of the keys. Sometimes focusing on a more relaxed playing technique can reduce strain on the hands when dealing with heavier action.
Weighted Key Practice: Though your DGX-650 has a heavier action than typical, you might treat it as an opportunity to build hand strength. Practice on it for a while, and when you move to lighter action pianos, it will likely feel much easier to play. It’s not a perfect solution, but it can be a way to adapt.
External Keyboard: If you plan on sticking with the DGX-650, but want a lighter action for certain pieces like the Minute Waltz, you could connect a MIDI controller with a lighter action to your Yamaha. You’d still be using the sounds from your DGX-650, but you could get the benefit of a lighter touch.
Consider a New Instrument: If this is a recurring issue and you’re finding the DGX-650 consistently uncomfortable for your playing style, you might consider upgrading to a digital piano with a lighter and more balanced key action. Something like a Kawai ES series or Yamaha’s higher-end models may offer the lighter action you’re looking for.
It's a tough situation, but if you play other pianos more easily, maybe transitioning to a lighter-action instrument could make your overall playing experience more enjoyable!
----------------------
https://www.pianos-galore.com: The Resource Site for Piano Enthusiasts