I am using a Rupert Neve RNHP from my 252 for occasional headphone use.
Today I wanted to check how my Shure 535 in ears perform with it and it is acting quite odd. My other low impedance open back headphones perform wonderful, but the Shure (36 Ω) creates a strange birdlike noise when nothing is playing and when playing they sound very thin and strange.
Switching back to cheap Yamaha open backs (48 Ω) and the problem is gone.
Plugging the Shures in my iPhone and they sound great. I have the Shure since 2015 and it never gave me any issues, so I am wondering where the fault lies.
I have tried 4 different adapters and the problem persists. Also tried an av integrated amp here with adapter and that is dead silent as it should be.
The sound makes me think of a slipping conveyor belt. It might be dc or ground related, or the Naim amp hum coming through. The Shures are known to be quite sensitive. But considering the other headphones have a somewhat similar impedance, I am a bit puzzled.
I tested a third pair of headphones and the noise is there. Somewhat less present, but there nonetheless. I suppose the Shures are very sensitive indeed, the cheap Yamaha’s aren’t at all and the last pair are in between.