hmscott
Addicted to Fun and Learning
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- May 17, 2020
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Nice description. I'll check later and post.Thanks for the reply, the noise is audible from outside the unit, both in the power cord area and in the rest, but you must bring your ear close to it and be in a quiet room, otherwise being very light it is not easy to notice. The noise does not spread through the cables from what I could see and hear, through XLRs are completely silent while if I go from RCA to M gain at high volume (3/4 of pot volume) I can hear some noise floor (it could also be the famous hum of the ground loop you guys were talking about in the previous posts). Both the D90 and the A90 are plugged in a filtered EMI/RFI power strip that is connected to wall. The D90 is fed by USB, but I tried in Optical too, the “hum” noise is exactly the same on RCA, so I think it’s actually ground loop noise and not source dependent, my source is actually surprising silent and interference free from what I can see, If I do the same test but with DAC off, I can’t hear any “hum” noise even at max volume on H gain on my headphones. I think this case of “hum” ground noise is pretty normal and easily remediable with a ungrounded high quality Power cord.
BTW, I'm not hearing what I consider "AC hum" when the RCA cable is connected. I only hear the USB crackle.
In H Gain with the USB cable disconnected I get a high pitched oscillation sound at Zero volume that only happens in H Gain switched on with XLR and RCA cables connected. It's definitely not "AC hum", as that has a distinct low frequency AC cycle tone.
Fortunately, with the XLR cables connected and the RCA cables disconnect in XLR only mode with the USB cable connected it is dead silent in all A90 Gain and Volume settings.
Both my XLR and RCA cables are 0.5m. Hifigo may get me shorter RCA / XLR cables and a split power / data USB cable to compare, I'll update about that later too.This noise floor discussion with regard to RCA connection made me curious so I tried both shorter and longer RCA cables between D90 and A90 and I can not hear any noise even in high gain at max volume level. I am using USB connection (same cable that came with D90) to D90 from my PC.
RCA cables are also cheapo cables (shorter one came with my iFi micro iDSD black label and longer one is just cheap generic RCA cable).
How short in inches / cm's is your RCA (XLR?) cables?
I haven't tried the included USB cable... I'll try that later too.
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