AUNE - MINI USB DAC/Headphone amp

[kmtang]

Hi all,

I bought one of this toy from EBay a week ago and I received the parcel in couple of days. It came with a +12Vdc power adapter. After listening to it for a day, I started the modifications to it that I hope to get better sound out from it.

I modified the DAC to work with a Power-One HAA15 stabilized power supply supply module. The PS module was set up to provide +/- 10Vdc for the DAC.
Also, I replaced 4 pcs of 1000uF 25V capacitor for the +/-VCC bypass with Blackgate 2000uF 16V one.

I had it hooked up to the Denon CD player to the SPDIF input. It sounds pretty good but lack the brightness in the treble and highs. I set up my PC to link to the DAC through the USB. It sounds much better and the treble/highs were clear and sharp - that's what I want.

That make me wonder how I could further improve the sound quality with SPDIF input??? Any ideas how to do it?


Best regards,
Johnny Tang
Vancouver, BC, Canada

[kmtang]

Here is the schematic.

[kmtang]

After reviewing the schematic for sometime, I decided to modify this DAC to remove the transistors from the headphone amp and strapped the Op-Amp as 1:1 buffer. Then, remove the input coupling capacitors and take to buffer output to the RCA jack.

This would provide better buffering from the DAC to the line amplifier. Also, I could use the volume and the DAC can be connected directly to any power amplifiers.

After this mod, the sound from the CD players sound more brighter that I would expect.

Now I can enjoy my CD collections all over again.

I am wondering how to squeeze more juice from this DAC, any ideas??


Johnny Tang

[kmtang]

As per DIR9001 datasheet - when it is not using external clock source, the XTI pin of the DIR9001 must be connected to the DGND. I had the DAC opened up and soldered a small piece jumper wire to connect the DIR9001 XTI input pin 8 to the DGND for a trial because I found the sound from the CD SPDIF source wasn't quite right, kind of too mellow.

After this fix, the sound from the CD - SPDIF source became much for solid and dynamic. It is quite similar to the character from the USB source. I was very surprised with this change.

I can't say this is a design fraud but I firmly believe this should be the right kind of sound it should be. I hope someone could try it and see whether they like this change.

Comments are very welcome.

JOhnny

[kmtang]

I brought this little DAC to my friend's home on Saturday. He is having Linn amplifier system with Sonic Frontier DAC.

Thanks for the latest DA technology, the AUNE has much better definition, dynamic and crystal clear. We could hear those small small sound details that we never heard before.

Good buy for AUNE but I need to explore for better one from now..


Johnny

[gwillys]

recap with elna rsf
burson regulator
burson clock w/±1ppm tcxo
burson opamp

sounds great. transformed.
next up are the 3 voltage regulators.

[gwillys]

btw - the general consensus is that this dac sounds best with 18v psu.

[kmtang]

Hello gwillys,

Please note that the max input voltage of the LT1117 voltage regulator is 15Vdc only. Check the datasheet to make sure before you increase the +/-10V to +/-18V. I think you may use one more regulator to lower the +18V to 10V before feeding to the 5 and 3.3V regulators.

Johnny

[kmtang]

Hi gwillys,

One more questions, it seems you put the burson oscillator to the PCM2707 USB interface chip. What about the DIR9001? Did you add the TXCO to it? If not, I would recommend you to ground the XTI pin of the chip, it improves the sound significantly.


Johnny

[gwillys]

hi johnny.
all you need to do is check input voltage on the 3 regulators. you will see it is good.
maximum 24v psu though.

your over my head re: clock. maybe you could explain further. are you saying the DIR9001 doesn't use the clock?