[dg3f]

i modified amb's gamma-1 to a usb dac without any other type of power supply as the following schematic,it sounds wonderful,but when i pluged my in-ear,high sensitivity earphone such as e5c or tf-10pro,it would come up with small and constant noise.These noise never happen to a Big size headphone such as my hd580,k701 and so on.

why it produces these boring ,low but observable hiss?

and what can i do to eliminate it?

p.s.:i have checked amb.org for gamma-1's info and found a note saying that background hiss will happen once input selector is employed,but i haven't use one.

here is my layout

 

[pistolsnipe]

i would ask in the grub dac thread, he basically designed what you have also


http://www.head-fi.org/forums/f6/grubdac-445155/

 

[ShinyFalcon]

Are you inserting your headphones direct from the DAC? Normally you don't... you have to hook them up to an amplifier. If you want to use headphones directly from the DAC you need to change the output caps to 470uF. You risk damaging the DAC with such a low impedance load (your headphones).

 

[amb]

WM8501 can drive low-Z loads, no problem (rated down to 16 ohms). But on very sensitive IEMs you might hear hiss. There is not much you could do about it other than using a resistance adapter to cut down the sensitivity, but that has its own set of sonic issues.

And yes, you'd need at least 470uF output caps for such loads or you'll have bass rolloff.

 

[amb]

P.S. Swap in a WM8759 instead of the WM8501 would help. It has 4dB less "gain".

 

[dg3f]

but today , these hiss seem to get louder,becoming a little unacceptable while my normal mp3s sound less noisy than my dac

i don't think using a headphone amp will help because the noise output from the amp will be no less than from the dac, isn't it true?

 

[ShinyFalcon]

I'm hearing hiss with my IEMs direct from y1 as well. It's probably about as hissy as some of my DAPs. If I use my Mini³ then I don't hear any hiss with my IEMs.