Rakesh_sharma23 provided us with a good review of the Xonar U7, so for pictures and a description, please visit the thread he started:
http://www.diyaudio.com/forums/pc-based/268678-asus-xonar-u7-usb-soundcard-review.html
The specifications on this external USB sound card looked interesting, so I bought one and did some measurements. The following picture says a lot:
Asus's claim of 0.0006% @ 1kHz is confirmed by this measurement. The distortion is dominated by the 3rd harmonic. An FFT showed a low level 50Hz supply related peak with an extended harmonics series following it. Since I don't know what the origin is - it might be that my laptop is dirty - I want to do some experimentation first before showing results.
All of this is pretty good from an unshielded plastic box measuring 14x8x2.7 cm on USB power and nothing to worry about. But I want to do better. The goal is to use the device as DA end for a PC based FIR crossover and I am fairly compulsive about measured quality, so that's why. It would also be nice to be able to use this device for measurements, for which it is unsuited at the moment.
The first step will be to replace the opamps. Presently, there are mini soic opamps mounted with the inscription 43K5 2A3. I can't find any reference to these opamps anywhere, so out of curiosity, if someone knows what they are, I'd be much obligated.
The replacement opamps will be OPA1642, a TI JFET opamp which at least on paper looks impressive. I ordered from HK because the prices there at small quantities are about 1/3rd of those offered by the M.F.D-K.RS gang. That means at least a 2 week wait, but I will keep you informed about progress, and in the meantime, if anybody has experience with modifying the U7, please share.
http://www.diyaudio.com/forums/pc-based/268678-asus-xonar-u7-usb-soundcard-review.html
The specifications on this external USB sound card looked interesting, so I bought one and did some measurements. The following picture says a lot:
Asus's claim of 0.0006% @ 1kHz is confirmed by this measurement. The distortion is dominated by the 3rd harmonic. An FFT showed a low level 50Hz supply related peak with an extended harmonics series following it. Since I don't know what the origin is - it might be that my laptop is dirty - I want to do some experimentation first before showing results.
All of this is pretty good from an unshielded plastic box measuring 14x8x2.7 cm on USB power and nothing to worry about. But I want to do better. The goal is to use the device as DA end for a PC based FIR crossover and I am fairly compulsive about measured quality, so that's why. It would also be nice to be able to use this device for measurements, for which it is unsuited at the moment.
The first step will be to replace the opamps. Presently, there are mini soic opamps mounted with the inscription 43K5 2A3. I can't find any reference to these opamps anywhere, so out of curiosity, if someone knows what they are, I'd be much obligated.
The replacement opamps will be OPA1642, a TI JFET opamp which at least on paper looks impressive. I ordered from HK because the prices there at small quantities are about 1/3rd of those offered by the M.F.D-K.RS gang. That means at least a 2 week wait, but I will keep you informed about progress, and in the meantime, if anybody has experience with modifying the U7, please share.
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Nowadays I pretty much ignore 50Hz. Too often it comes from interactions between equipments. For example you may not get it with self-loopback measurements, but you see it when connected to another measuring equipment or an amplifier. Then play with grounding and SE/BAL to make it go away.
And this affects not just 50Hz but also whiteband noise. I reckon it affects distortions also but I have not proof of that.
Makes one wonder, if a products measures superbly good in a particular test setup but totally flunks it in typical usage environment, does it still count as a good-measurement product? (Sound cards I'm looking at you, especially certain USB DACs.)
Anyway 0.006% isn't all that good. You might want to try if your integrated sound can hit that level already.
And this affects not just 50Hz but also whiteband noise. I reckon it affects distortions also but I have not proof of that.
Makes one wonder, if a products measures superbly good in a particular test setup but totally flunks it in typical usage environment, does it still count as a good-measurement product? (Sound cards I'm looking at you, especially certain USB DACs.)
Anyway 0.006% isn't all that good. You might want to try if your integrated sound can hit that level already.
Wwenze, you are right, 0.006 is not that good, my laptop does that too. I now see I forgot a zero, I edited it right in the first post, so this is just to let you know that you read it right the first time.
In the review you linked to below into post one he writes "ZA3 are Texas Instruments LME49726 Series Audio Op Amplifiers", so seems the print is ZA3 not 2A3.
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