Feixiang FX-98s PCM2704 + XR1075 +QS7779 USB DAC - Page 2 - diyAudio
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Old 9th January 2014, 05:18 AM   #11
roggom is offline roggom  United States
diyAudio Member
Join Date: Apr 2008
I will post the pics within the next few days. It was a simple jump of the opamp. Now if you desire to use as a headphone amp, maybe try a higher value resistor as the increase of feedback lowers gain, but seems to push the noise floor a little higher (when using headphones). As a preamp, the sound is very transparent with the volume knob from low to mid level.

I do still hear the 1 khz, but I have not troubleshot with my scope yet. I honestly believe it is the PCM clock that is causing the noise.

I removed the XR1075 chip and the noise is completely gone, that is because it breaks the signal path , so I can only assume the origin is before the xr1075. I did some trace routing, but it is very difficult with black mask over the board.

I am sure with a little more troubleshooting, the noise can be illuminated, but my guess is the PCM/DAC must be disabled to do so.

Most of my Google searches for DAC hiss, suggested upgrading DAC's. There just has to be a way to illuminate it, either by upgrading to a much better opamp, or active filtering.

we will see.
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