I have a Yamaha P45 digital piano and various headphones:
HD 598SR
ATH M50X
DT 770 (250 Ohm)
The P45 has a 6.35mm jack and I tried it with various headphones and adapters/cables.
All headphones had this annoying static or wind noise when I turned the piano. It is constant in volume and not too loud, somewhat quiet. I did notice however that with high impedance headphones (DT 770) the noise was reduced in volume quite a lot.
Im mainly using the ATH M50X though as it is the only headphone I have with a direct 6.35mm jack all my other headphones are 3.5mm with 6.35mm adapters and the adapters always give me crackling issues.
What about a really cheap ups, or perhaps replacing the power adapter?
The power adapter is the original one supplied by the manufacturer, but its small and looks supper shoddy and flimsy.
What about impedance matching? I heard that in general anything that uses 6.35mm socket requires headphones with higher impedance. So my ath m50x which has relatively low impedance has the issue but my 250 ohm dt 770 doesn’t.
Could try something like the Palmer Purifier which plugs in between PSU and keyboard (or headphone amp, guitar pedal, etc.)
The connector of the headphone has nothing to do with its impedance.
The M50x are 38 Ohm. When the built in headphone amp in the AP45 is class A, you will always have some current flowing. The M50x may just be sensetive enough to produce sound from that.
I don’t think there is an easy way to get rid of the noise.
Sorry I meant where would you find the specific specifications for the amp for the headphone output, I know what a amp is. I didn’t even know it was energy class A.