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1/8 Source Impedance Rule of Thumb, Split from "Audible Differences in DAC's?"
post Feb 25 2013, 18:25
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QUOTE (Arnold B. Krueger @ Feb 25 2013, 07:51) *
QUOTE (mzil @ Feb 24 2013, 16:10) *
QUOTE (Arnold B. Krueger @ Feb 24 2013, 05:58) *
Agreed. However a FIIO E3 plugged into a UCA 202 gets you there for less than half of that.

If I am understanding you correctly, you are suggesting bypassing the built-in headphone out already found on the UCA-202 and instead using its line out to the Fiio E3 to drive some headphones?

BTW I made a typgraphic error above. I meant FIIO E5. I had to look at the one on this computer to refresh my memory! ;-)

Yes. The headphone jack on the UCA 202 has a source impedance of about 50 ohms which can lead to audible frequency response changes with some headphones.

The Fiio e5 is said to provide a source impedance of less than 1 ohm:


^There is (or was) an E3, but it lacks a volume control and is not well thought of by nwavguy, so I wasn't sure what exactly you were suggesting. Thanks for the clarification.

Regarding the Behringer UCA202's output impedance spec of 50 ohm for the UCA202 and driving low impedance headphones, I suspect the importance of strictly adhering to the "1/8th rule" is a bit exaggerated. He only shows a worst case scenario, his Ultimate Ears SuperFi 5 Pro, and from there scares everyone into accepting this rule as gospel. I really wish I could see more curves than just that. For all we know the amount of deviation plummets with a conventional, non-balanced armature design with a similarly low impedance, or if one accepts deviations of say +/- 1 dB as being relatively benign (considering the much larger, comparatively rollercoaster curves of different headphones in general, one model to the next), his "rule" becomes more like "1/2" or "1/4" , for all we know. Your thoughts?

This post has been edited by greynol: Mar 14 2013, 01:53
Reason for edit: Added quote which links to the original discussion for context
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