FIRST IMPRESSIONS: NEW Nuforce uDAC-2 with 24/96 - USB DAC AMP with line out and S/PDIF out
Oct 1, 2010 at 7:41 PM Post #301 of 877

IsoOctane

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To pursue the attenuation idea, I rigged up a pot in series with my headphones and set out to find how much resistance I need to just get the tone below hearing threshold / background noise (it's very quiet in the room though). The value needed was pretty much 100 ohms, which translates to 0.24 factor in voltage assuming the nominal headphone impedance of 32 ohms and neglible output impedance in the uDac. That means a bit over 12 dB in sound pressure level, maybe that tell's someone something about the volume of the tone.
 
Now, the problem with just putting a resistor in series with the phones is that if and when the impedance curve of the headphones is not perfectly flat, you will get a variable voltage drop at the resistor depending on the frequency. Looking at the impedance curve measured by Headroom, the maximum deviation seems to be around 33% for my Denons, and I calculated that this translates to about 1.8 dB deviation in the volume when using a 100 ohm resistor in series.
 
Is that something that could be perceived? 1.8 dB deviation in the frequency response in exchange for 12 dB reduction of noise. Anyway, the deviation can be reduced by using another resistor in parallel with the headphones which effectively acts to flatten out the impedance curve. So for example, putting a 10 ohm resistor in parallel and a 24 ohm resistor in series should give the same attenuation, 31 ohm total impedance, but only 0.4 dB deviation in the frequency response. Anyone tried something like this before? I guess I need to buy some resistors and try it out and hope my calculations are correct.

 
Quote:
I am just wondering for those who heard the strange noise - did you turn off all the power-management features under Windows, for example, in Windows 7, the O/S could generate noise if you don't turn-on Exclusive Audio and turn off 'let Windows manage volume', etc.
 


 
I hear the tone even when connecting to an externally powered USB hub that's not connected to anything itself.
 
Oct 1, 2010 at 7:51 PM Post #302 of 877

IsoOctane

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Quote:
Let's all try to answer this list and maybe we can conclude something:
 
1.  Can you hear the tone? ( if no, jump to question 9)
2.  Is the tone louder than the background hiss? (a feel for how loud it is)
3.  Does the tone change volume with the volume knob turning?
4.  Estimate the frequency of the tone
5.  Does the tone frequency change with different headphones?
6.  Try different usb ports on the computer, does the tone change volume or frequency or is it identical on every port?
7.  Does the tone occur anytime the udac2 is plugged in and on, whether it's playing anything or not?
8.  Is there a tone if you plug it into a usb charger or hub without being connected to a computer?
9.  List the computer(s) it is connected to and if any hub or extension cable is in between.
10. List the usb cable you are using it with.
11.  List the headphones you hear and don't hear it with.

 
1. Yeah...
2. Apart from the tone, I don't hear any other hiss or noise even when turning the volume all the way up.
3. No.
4. 2500 Hz for my first unit, lower for the second but haven't measured.
5. No
6. It's identical.
7. Anytime the unit is on.
8. USB hub, WLAN modem, IPTV-box, in all cases the tone remains.
9. Mostly connected to my i3 desktop with Intel board and Seasonic X-400 PS. Tried with other computers too.
10. Original + some random other cables.
11. I hear it with Denon AH-D1001 and some cheapish Sennheiser ear-buds.
 
Oct 2, 2010 at 3:26 PM Post #305 of 877

grokit

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Quote:
1. No
9. IMAC late 2009 (10.6.x), Dell notebook (winxp), no hub
10. original, atake retractable
11. sr60i, ms1i, cx400, pl30


I would bet that Mac users without hubs are unaffected by the noise issue, while some PCs are better than others.
 
Oct 3, 2010 at 10:44 AM Post #307 of 877

lonereaction

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Quote:
XP + foobar + asio4all = win7 + foobar + WASAPI
 
but if you aren't using asio4all and using the windows mixer, then WASAPI > windows mixer


 
I've just downloaded the WASAPI plugin and put it in the appropriate folder. Is setting the output to WASAPI: SPDIF Interface (NuForce uDAC 2) and set it at 24bit. Is that all I need to do?  Thank you!
 
Oct 3, 2010 at 3:03 PM Post #309 of 877

grokit

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Just get a second one or use Velcro instead 
etysmile.gif

 
Oct 3, 2010 at 10:59 PM Post #311 of 877

bcwang

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Quote:
 
I've just downloaded the WASAPI plugin and put it in the appropriate folder. Is setting the output to WASAPI: SPDIF Interface (NuForce uDAC 2) and set it at 24bit. Is that all I need to do?  Thank you!


Yes, and just make sure your volume is at 100% in foobar and 100% in any relevant windows audio control panel for the uDac2.
 
Oct 4, 2010 at 7:51 AM Post #312 of 877

JackG

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Quote:
 
I've just downloaded the WASAPI plugin and put it in the appropriate folder. Is setting the output to WASAPI: SPDIF Interface (NuForce uDAC 2) and set it at 24bit. Is that all I need to do?  Thank you!

 
 Sorry for the OT piggyback but I did this and now playback is stuck in fast-forward mode...any ideas? 
 
 
Oct 5, 2010 at 12:08 PM Post #314 of 877

replytoken

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Well, a bit of experimenting with external USB hubs proved interesting.  Plugging the uDAC-2 into a USB AC charger produced a flury of static.  And plugging the uDAC-2 into a powered USB hub not connected to a computer also produced a flury of static.  However, plugging the uDAC-2 into the USB hub without using its power supply mostly eliminated the high-pitched noise, as it became somewhat intermittent.  Given this, I think that I want to double check the USB cable, and then try my netbook and some other machines to see if this will shed some more information.  Very frustrating.
 
--Ken
 
Oct 5, 2010 at 4:48 PM Post #315 of 877

palhenf

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Quote:
Originally Posted by bcwang 

Let's all try to answer this list and maybe we can conclude something:
 
1.  Can you hear the tone? ( if no, jump to question 9)
2.  Is the tone louder than the background hiss? (a feel for how loud it is)
3.  Does the tone change volume with the volume knob turning?
4.  Estimate the frequency of the tone
5.  Does the tone frequency change with different headphones?
6.  Try different usb ports on the computer, does the tone change volume or frequency or is it identical on every port?
7.  Does the tone occur anytime the udac2 is plugged in and on, whether it's playing anything or not?
8.  Is there a tone if you plug it into a usb charger or hub without being connected to a computer?
9.  List the computer(s) it is connected to and if any hub or extension cable is in between.
10. List the usb cable you are using it with.
11.  List the headphones you hear and don't hear it with.

1. yes
2. yes (hear no hiss on hp desktop, some hiss at high volume on lenovo x301)
3. no
4. 10k?
5. no (present on shure ec4, non existing on koss porta pro etc)
6. identical on all ports, pcs/mac, usb hub etc
7. yes
8.-
9. hp desktop, lenovo x301, macbook pro, with/without usb hub powered by pc
10. original
11. shure ec4 (29 ohm)
 
Does anyone know if this problem is existing on the first version of the Nuforce uDac? Is there a big quality difference between uDac and uDac2? I read that the uDac anyway can be upgraded to support 24 bit/96 kHz, so I'm considering to test it as a replacement.
 

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