Symmetric Output for USB Audio DAC

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This simple adapter circuit is specially intended for use with the USB Audio DAC
published in this website elsewhere. With an easily implemented
modification, it is possible to make the output of the D/A converter
pseudo-symmetric, so that it can be connected to professional equipment
having XLR line inputs. This will do even more justice to the high quality of the USB Audio DAC.
The modification actually amounts to just adding a single resistor
(R11a) and changing the value of the existing resistor at the output of
the audio DAC (R11) from 100 Ωto 68Ω.
Components C14 and R12 remain unchanged. It is not difficult to make
this change on the printed circuit board of the audio DAC,
but a bit of improvisation is necessary. After replacing R11 with a
68-Ω version, unsolder R12 and connect R11a in series with it. Bring out
the junction of these two resistors to act as the signal return
connection (pin 3 of the XLR socket). The same
operation must also be carried out on the right channel, where the
affected resistors are labelled R16, R16a and R17.


Circuit diagram