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+--- Thread: Loud Electrical Hum from Sub Preout when units are in Standby! (/Thread-Loud-Electrical-Hum-from-Sub-Preout-when-units-are-in-Standby)
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RE: Loud Electrical Hum from Sub Preout when units are in Standby! - ogs - 17-Feb-2018
I knew I'd read this somewhere. It used to be on the Devialet web site, but it is not there any more. I found a reference in this post at whatsbestforum: http://www.whatsbestforum.com/showthread.php?1856-Has-anyone-heard-the-Devialet-D-Premier-Integrated-Amp-DAC&p=30237&viewfull=1#post30237
So even the signal on RCA connectors is balanced or differential. This is of course very good as long as the amplifier is on and active, but not so good when it is off as ground is not terminated (the ground on a single ended input is connected to one leg of a differential input). A shielded cable will probably avoid the noise while an unshielded cable would produce hum and noise.
RE: Loud Electrical Hum from Sub Preout when units are in Standby! - hardcore - 16-Aug-2019
I have the same experience but a little different, with a 250 Pro CI (and same after upgrading to a 1000 Pro CI).
I used to have my subwoofer connected via RCA directly. This worked fine and had no hum when the Devialet was on or off. But I always felt like the subwoofer's RCA connection was introducing noise back into the Devialet and affecting sound quality.
So I recently got a subwoofer RCA-RCA isolation transformer, and connected it between the sub and Devialet's RCA out. Now, when the Devialet powers off, the subwoofer will hum. My subwoofer has a 2-pin power input and is un-grounded.
BTW, the isolation transformer (a Jensen Iso-Max) does work - I think the Devialet sounds better with it. I find the sound quality of the Devialet improves noticeably with clean power and ground.
This indicates to me that the Devialet disconnects the RCA ground when powered off. To me this is actually somewhat of a good thing, as it indicates the Devialet's RCA outputs are internally not directly ground coupled, or 'differential' as the previous link mentions.
RE: Loud Electrical Hum from Sub Preout when units are in Standby! - yanc - 25-Mar-2021
Yes +1 ^^^
Introducing a SUB to my system brought back those lower frequencies and a sense of fullness (mostly for electronic music), but I agree I also feel like the subwoofer's RCA connection is introducing noise back into the Devialet and affecting sound quality.
I 've tried various cables, RCA caps, but the degradation is still there. Kind of like an artificial layer is added to the sound, across all frequencies.
Same set up here. Single RCA going to a 2 RCA input on the SUB using the left channel only (as per B&W608 instructions)
Looks like RCA-RCA isolation transformer must be the only solution
RE: Loud Electrical Hum from Sub Preout when units are in Standby! - Delija - 27-Mar-2021
Do you use high-pass filter in combination with subwoofers?
RE: Loud Electrical Hum from Sub Preout when units are in Standby! - yanc - 27-Mar-2021
No. Should I?
I set the subwoofer low-pass filter at 60Hz (filter order 2).
My speakers don't go below 50 (55?) so I leave them full range.
Lately I started feeling that the sound quality issue I have has to do with enabling sub out function at the amp level (dp_cfg).
and not necessarily with the cable connection. i'm still investigating...
RE: Loud Electrical Hum from Sub Preout when units are in Standby! - Delija - 27-Mar-2021
No, you shouldn't - because it deteriorates the sound.
I don't hear any difference in sound quality if I turn or or off preout for subwoofers.
RE: Loud Electrical Hum from Sub Preout when units are in Standby! - yanc - 29-Mar-2021
problem solved!
after countless tests and recabling (now, this is a good thing with the lockdown!)
there were 2 issues :
(1)
SUB needs to be fed from the same power source as the DEV to avoid ground loop buzzing,
(2)
with the SUB I also replaced my mac.mini external drive to a 2TB SSD, without paying much attention to the USB port connections, so that:
- the SSD ended up on the USB1 port (my mac.mini 2012 has 2 of those!), and
- the DEV-DAC ended up on the port that is shared with the Bluetooth controller.
Changing these to the 2 exclusive USB2 ports fixed the sound quality issue!
P.S.
now the problem is that
- I need to use a very long power cable to connect the SUB and,
- the SUB's Auto power mode doesn't seem to work, and needs to be ON all the time (not sure this ever worked)
