Author Topic: DAC - THD + Noise @ 1kHz  (Read 242 times)

David Samborsky

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DAC - THD + Noise @ 1kHz
« on: August 28, 2020, 02:58:04 AM »
Test Results:


Conclusions:

The Ultimate-Preamp 2/+ has vanishing low levels of distortion and noise, so much so that it is approaching the limits of our dScope III audio analyzer. Even at much higher output voltages compared to your typical DAC the UP2/+ does not disappoint as shown by the following screen shots of the THD+N measurements 😁 The difference in distortion between the two channels is most likely due to the differences in the analyzer ADC and not the Preamp because reversing the channels does not appear to have any effect on this 😉 To get better measurements we would need access to an analyzer such as the Audio Precision APx555 which nulls out the fundamental so that it can more accurately read the harmonics from the output of the Preamp rather than the added distortion from its own ADC. However, we are not complaining about these results because it looks like all of the work we have done on the DAC and post DAC circuitry in this new Preamp has payed off

The THD + Noise performance of the unbalanced output is a whisker higher than the balanced output but still does not disappoint ! Below 1kHz one can clearly see the mains artifacts that are not present in the balanced output spectrum but are still buried way down below the threshold of hearing of -120dB and so of no concern !! These artifacts are caused by leakage flux from the transformer used in the linear power supply 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 !! Above the 1kHz fundamental test signal we can see the usual harmonic distortion spikes mainly attributable to the distortion of the ADC used inside the analyzer. There are no spurious noise spikes from an external switch mode power suppliy simply because we don't use one and the on-board switching regulator used to power all of the digital circuitry runs at 500kHz which is well outside the audio bandwidth !
« Last Edit: September 05, 2020, 01:55:14 PM by David Samborsky »
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David Samborsky

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THD + Noise (Balanced Output)
« Reply #1 on: August 28, 2020, 06:01:18 AM »
Output level of 25dBU = 13.7 VRMS on Channel-1/2



Output level of 3 VRMS on Channel-1/2



Output level of 1.9 VRMS on Channel-1/2

« Last Edit: September 01, 2020, 09:55:41 AM by David Samborsky »
The home of the Ultimate-Preamplifier and Ultimate-Amplifier ! https://www.analog-precision.com/

David Samborsky

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THD + Noise (Unbalanced Output)
« Reply #2 on: August 28, 2020, 09:29:53 AM »
THD + Noise spectra and RMS voltage of Channel-1/2 unbalanced output

« Last Edit: September 01, 2020, 09:55:56 AM by David Samborsky »
The home of the Ultimate-Preamplifier and Ultimate-Amplifier ! https://www.analog-precision.com/