ROCK NUC via USB creates hums and crackles

As per my previous post my system comprised of NUC ROCK → ROON Ready Auralic Mini → RCA to AMP. I noticed hum and crackle noise when system is idle (cannot confirm they are still there when sound is playing).

Since then i replaced the Auralic for a Topping D30 Pro and connected my system now as NUC ROCK → USB to Topping DAC → RCA to AMP. Unfortunately i still have the hum and crackle noises (not always to make it even weirder) but also the volume level is way lower than my other sources. The CD player and my TV (via Toslink), both directly hooked up to the AMP, play nice on -20dB, the ROCK source needs to be a 0dB to reach same level of sound.

So 2 problems, where does the noise come from? Why is the input volume so ‘low’?

To get a better idea i switched my TV with toslink to the DAC instead of directly into my AMP and experienced neither issues. No noises and volume level was equal to other sources on my AMP.

So the RCA from the Topping to the AMP and the AMP itself are not a part of the problem, but the USB connected NUC with ROCK is. The Topping came with a cable and i read on all serious forums this cable should suffice, quality-wise.

Any ideas? I heard something about groundloops. My AMP is not grounded. The NUC and DAC are.

So, as soon as you disconnect the USB hum stops?
Testing the earthed devices with a cheater plug may help reveal the source of the hum.

Make sure you’re not using volume leveling or have adjustments to headroom or volume in Roon.

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You don’t need a fancy USB cable, but you do need a working USB cable. Try swapping it with a different one.

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Hey Bill,

did just that yesterday evening and it seems solved now! I am going to listen carefully the coming weeks.

@marin_weigel: thanks for your input. I disabled all DSP from Roon during all my testing.

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Yeah, sometimes the stock cable just is bad. Glad to hear it’s fixed!

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Alas it seemed to be a fluke. The sound is yet again distorted and since the distortion was consistent i could do some tests. I tested all connection between different devices. Swapped RCA, no change, swapped USB back, no change. Disconnected NUC from DAC and put Toslink from my TV into DAC, no change. So this basically rules out ROON ROCK. Put the Toslink directly into AMP, no distortion. So distortion seems to be in the AUX in’s. Test both with DAC and Auralic Netwerk DAC, both distorted in both AUX in’s. So i took a CD-player - how simple device - and connected it to the AUX in’s. Distortion!!

So my conclusion is the AUX in’s from my AMP are defective. This could explain the randomness. The day after this test i had clear sound the whole day but yesterday it was fully distorted again. So i will bring my AMP to the repair shop to get it checked out.

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