Noise Performance (No Signal)

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Test Results:

• Noise performance - Balanced Output
• Noise performance - Unbalanced Output
• Noise performance - Balanced Output - A-weighted
• Noise performance - Unbalanced Output - A-weighted

Conclusions:

The noise floor of the balanced output of the UP/2+ is only 6dB above the noise floor of the dScope III audio analyzer which is approaching -116dBu or 1.2uV  RMS ! Bear in mind that unlike standard DACs we have incorporated a buffer amplifier on each balanced output to boost the output level from the output of the IV converters which will of course add some additional noise of its own. Also in the 2nd image capture below we have expanded the frequency axis from 0-1kHz to show the almost non existent mains components sitting above the noise floor which is a tribute to the balanced design.

The noise performance of the unbalanced output is slightly higher than the balanced out but still does not disappoint ! On the expanded frequency scale one can clearly see the mains artifacts that are not present in the balanced spectrum but are still buried way down below 120dB !! This is caused by leakage flux from the transformer setting up earth loops in the internal wiring from the DSP board to the Unbalanced output board. Yes folks balanced always wins out simply because common mode noise is cancelled out !!

dScope III Noise Performance:

• Unmodified dScope III Noise with inputs shorted

• Upgraded dScope III Noise with inputs shorted

• Upgraded dScope III Noise with inputs shorted (A-weighted)

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Noise spectra and RMS voltage of Channel-1/2 Balanced Output

Noise spectra above with expanded scale

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Noise spectra and RMS voltage of Channel-1/2 unbalanced output

Noise spectra above with expanded scale showing some very low level mains (50Hz) artifacts

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Some mains induced noise caused by leakage flux from the transformer coupling into the unbalanced connections between the DSP board and the unbalanced output boards in the same way earth loops are setup in unbalanced connections between equipment !. The balanced outputs do not exhibit this since the balanced connections between the boards cancels out the mains induced noise ! However the mains induced noise components on the unbalanced outputs is still 120dB below the reference level so we don't have to lose any sleep over this