I recently bought the Audio-gd NFB-12.1 to pair with my Q701's and after using it for a couple of days, I have to say, i'm not very pleased with what i'm hearing. I'm using the Q701's as my primary set of headphones and i find the sub bass to mid bass to be pretty deep and defined but the vocals seem to be a little thin and the highs are not really clear and they too are a little thin and grainy.
I've been using my Q701's with a cheap CMoybb headphone amp from JDS Labs connected to the headphone out of my Xonad DX sound card and i find this combination to be cleaner and clearer with a better sound-stage as compared to the NFB (though i find the bass on the NFB to be better).
I tried to bypass the NFB's internal amplifier and instead connected the CMoy to the DAC out of the NFB. It turns out the DAC output sounds exactly the same as the headphone output. It seems as if the only difference between the headphone out and the DAC out is the type of connector used. I confirmed this by connecting DAC out at the rear directly to my Q701's using a 3.5 mm female to RCA converter. It sounds exactly the same as the headphone out with the same sonic characteristics that i wanted to avoid. The gain switch, the volume pot, the OS and the filters all work. Its as if I've connected my Q701's directly to the headphone output.
Does this mean that the NFB-12.1 cannot be used as a standalone DAC with the internal amp interfering? I'm going to buy the Schiit Lyr in a couple of weeks and really wanted to bypass the amplifier of the NFB (i'm not happy with its sonic characteristics) and use it as just a DAC. Could someone please shed some light on whats happening here. Any help would be greatly appreciated.