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Topic: Bargain USB DAC Modifications (Read 4388 times) previous topic - next topic
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Bargain USB DAC Modifications

This was mostly an academic exercise to see how much performance a person can get for a total of $35 from a USB DAC. But some here might find it interesting. I needed an inexpensive headphone DAC and had a $29 Behringer UCA202 laying around. In testing it I discovered it performs better than expected but the headphone output was seriously limited. But $5 worth of parts and some soldering improved the situation dramatically.

DIY/design/measurement geeks might enjoy the "before" and "after" results:

UCA202 DAC Measurements Before Modification

UCA202 DAC Measurements After Modification


 

Bargain USB DAC Modifications

Reply #1 –
I must be an idiot because I see scads of harmonics that shouldn't be there after it got fixed. What am I missing?

G²

Bargain USB DAC Modifications

Reply #2 –
Quote from: Glenn Gundlach on
I must be an idiot because I see scads of harmonics that shouldn't be there after it got fixed. What am I missing?

I'm not sure which harmonics you're referring to? A big part of what's changed is the maximum output. So I show several spectrum graphs both before and after with the UCA202 near clipping where, yeah, the distortion is relatively high with lots of harmonics. That's normal for any device that's on the edge of clipping when you're testing the maximum output.

At the reference level of 400 mV, the THD+N of the modified version was only 0.0076%. The 2nd harmonic was the greatest at about -86 dB, the 3rd harmonic was down even further at about -95 dB, and everything above that up to 20 Khz is around or below -100 dB. In a $29 device, 0.0076% and harmonics this low is generally considered fairly impressive. The spectrum is shown below.

The ultrasonic "bump" that starts above the audible range at about 25 Khz is from the noise shaping used in the TI/Burr Brown DAC and it's equally present in both versions.

Are we talking about the same harmonics or did you have a different question?