HELP: PC (USB) problems with Subwoofer LOUD white noise - diyAudio
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Old 4th July 2011, 03:28 AM   #1
sunil is offline sunil  India
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Default HELP: PC (USB) problems with Subwoofer LOUD white noise

Hi,

I have a PC based audio setup (Ubuntu /USB). The USB output feeds a Firestone DAC that goes to an Audiolab preamp. The preamp feeds a Behringer 2310 and from there to the power amps. A subwoofer (Dayton 315 with Oaudio 500) is connected to the pre-out on the preamp.

PC (USB) --> DAC --> Preamp --> Behringer active X/O --> Power-amps

Preamp --> Subwoofer

Pulseaudio is used in Ubuntu and the volume is disabled. The DAC volume is set to ‘shunt’ mode and the pot fixed at 12’o clock.

Most program material plays fine. If there is deep bass and/or the volume is turned up the USB stream gets cut-off and replaced with very loud white noise from the main speakers. Turning the volume on the preamp down stops this. Restarting the audio player in Ubuntu (Audacious) does not bring the music back completely. There’s noise riding on the signal & the audio bit is very feeble.

Switching the amps and DAC off brings it back online, till the next ‘white noise’ break. So far, I’ve been able to play the system without problems if the SUB is switched off completely.

Weird – I don’t know, why – I have no clue. Has anybody seen this before ?
Can somebody please help me understand how to fix it.

P.S: If the moderators think this is in the wrong forum, please move accordingly – Thanks.

Thanks,
Sunil

Last edited by sunil; 4th July 2011 at 03:30 AM. Reason: Corrected the line drawing showing the setup
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Old 4th July 2011, 06:20 AM   #2
erin is offline erin  Australia
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Just a suggestion. I have had USB audio signals disrupted by mains borne interference such as motors switching on and off. Perhaps the subwoofer is drawing a large current and causing mains spikes or fluctuations during loud passages?

The exact cause I dont know, but the point I am trying to make is that USB audio is not always 100% reliable when there is RF interference or mains disturbance.

Perhaps try using a shorter USB cable?
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Old 4th July 2011, 04:02 PM   #3
sunil is offline sunil  India
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Thanks Erin. Separating the PS for the SUB is a huge task. What I can't understand is why it happens only when the volume is turned up ?

Anybody with opinions /experience, please help ?
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Old 5th July 2011, 12:03 AM   #4
erin is offline erin  Australia
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Sunil, I was not suggesting to relocate the power supply for the sub.

How long is the USB cable you are presently using?
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Old 5th July 2011, 12:58 AM   #5
sunil is offline sunil  India
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I've tried the stock 1m cable, an extension 3m, both shielded and with a hub. The only thing left to try is a different power outlet because all the ones in the present rm are looped to the same line

The PC is ~3m away from the system console which makes it harder, cause then I have to go with longer RCA's. Do you think that makes better sense ? I'm also seriously thinking of a good soundcard, in the lines of ASUS , if this setup does not work.

Regards,
sunil
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Old 5th July 2011, 01:16 AM   #6
erin is offline erin  Australia
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I know someone who uses an Asus Xonar D2X (spdif output) powered with external linear power supplies and he thinks its very good. I have not heard it but I trust this persons opinion.


It seems like the problem is related to the sub. Is it a Class D amp inside the sub?
I wonder if it has CE, C tick, FCC approval? perhaps it outputs exceessive noise?

does the firestone DAC use an external (wall wart) power supply? I wonder if when the Sub is playing loudly that the vibrations are momentarily dislodging the power connector either at the power board or the DAC end?

Last edited by erin; 5th July 2011 at 01:22 AM.
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Old 5th July 2011, 02:16 AM   #7
sunil is offline sunil  India
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I can't see any of those approvals on the plate amp. It was bought from Oaudio.
The problem is definitely the SUB.

The DAC does use an external supply, but its a tight fit on the power strip so I doubt the SUB is dislodging it. About the ASUS I was thinking of the 'Essence XT' since it has RCA out.

Looks like I'm out of options ?
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Old 5th July 2011, 02:32 AM   #8
erin is offline erin  Australia
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My last thoughts on the matter, are for you to try adding larger capacitance to the power rails of the DAC, or using a different preferably linear power supply ( with big capacitance), ferrites on your mains power leads, and perhaps seperate inline filters on the SUB and on the DAC. Perhaps the heavy power draw of the SUB is causing a voltage drop in the DAC causing it to loose comms with the computer?
Larger capacitance will keep the DAC at full voltage long enough to withstand the short term voltage drop on the mains.
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Old 5th July 2011, 05:12 AM   #9
sunil is offline sunil  India
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Thanks Erin. I see my options as:

- Change the SUB ps to a different outlet
- Stiffer PS for the DAC
- USB2ISO isolator

I wonder if the US2ISO will solve the problems I'm having. It is explained as being able to isolate PC power problems. Could anybody please help me understand my situation ?

I'm posting this question on the USB2ISO thread to see if those folks have any idea about this.
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