Hello,
I was able to hear some hum noise...a mixture between 50Hz and 150Hz, especially when using my sensitive AKG K550 cans with volume to the max, of course...no input source connected! I know these sensitive 32-Ohms cans can be driven by only few dozen of mV only instead of 7V when volume to the max, but I know this DAC/headamp combo measured some hum by Archimago (here and here) and also by other people's RMAA, so I needed a way to test it myself without having a decent ADC around. So yes, the hum is there and audible.
If I was reclining or moving away the toroid trafo then hum was gone, actually...if I was opening the case the hum os not there anymore, so most likely the thick metallic case bounced back the EMI field into the nearby potentiometer or something. So yes: case open = no more hum; case closed and toroid in a different angle = hum lowered a lot...quite strange.
However, I fixed the hum noise for good by wrapping twice a band of "grain-oriented silicon steel" (G.O.S.S. band) around the toroidal transformer. Now there's absolutely no audible hum at all not with AKG K550 anymore and not even with my very sensitive 16-Ohms Superlux IEMs (quiet night, mute=ON, pot. to the max. = no hum at all!).
The G.O.S.S. band I got it from a friend who works as engineer for Petra-toroid (I got it for free, they don't sell this). Also Talema is implementing this as well in Hi-Fi equipment: http://www.nuvotem.com/en/products/gossband_large.shtml. So yes Sir, Faraday knew some shit.
I was able to hear some hum noise...a mixture between 50Hz and 150Hz, especially when using my sensitive AKG K550 cans with volume to the max, of course...no input source connected! I know these sensitive 32-Ohms cans can be driven by only few dozen of mV only instead of 7V when volume to the max, but I know this DAC/headamp combo measured some hum by Archimago (here and here) and also by other people's RMAA, so I needed a way to test it myself without having a decent ADC around. So yes, the hum is there and audible.
If I was reclining or moving away the toroid trafo then hum was gone, actually...if I was opening the case the hum os not there anymore, so most likely the thick metallic case bounced back the EMI field into the nearby potentiometer or something. So yes: case open = no more hum; case closed and toroid in a different angle = hum lowered a lot...quite strange.
However, I fixed the hum noise for good by wrapping twice a band of "grain-oriented silicon steel" (G.O.S.S. band) around the toroidal transformer. Now there's absolutely no audible hum at all not with AKG K550 anymore and not even with my very sensitive 16-Ohms Superlux IEMs (quiet night, mute=ON, pot. to the max. = no hum at all!).
The G.O.S.S. band I got it from a friend who works as engineer for Petra-toroid (I got it for free, they don't sell this). Also Talema is implementing this as well in Hi-Fi equipment: http://www.nuvotem.com/en/products/gossband_large.shtml. So yes Sir, Faraday knew some shit.