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USB dac supply ac noice problem?
USB dac supply ac noice problem?
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Old 17th October 2006, 05:06 AM   #1
pipp0r is offline pipp0r  Norway
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Default USB dac supply ac noice problem?

Hi I have an pcm2706 dac with an tda1543 output section. Im using a 230v ac -> 12vdc regulated supply -> then two regulated supplys using lm317 for two 5 volt rails. One for the pcm2706 section and one for the tda1543 section.

So to the problem. When other electrical equipment turn on and off the dac some times halts in windows, this meaning foobar output stops and I have to start the song again. Although not critical, this really is annoying. Im assuming this is a problem with noize on my AC. Is there anything to do with my supplies, or before the supply's, that will prevent this problem ? Some kind of spike protector on the AC inlet or something like that ?
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Old 17th October 2006, 10:36 PM   #2
dddac is offline dddac  Germany
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USB dac supply ac noice problem?
to see if the issue is really the power supply you use, you can try for a while a battery for the 12 Volt supply for the dac and the 2706 and see what happens....

I would any way use 8 Volt for the 1543 and according bias settings to get the max out of this chip

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Old 25th October 2006, 09:59 PM   #3
pipp0r is offline pipp0r  Norway
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Seems to be the powersupply. Would adding more smoothing caps have any effect ? Parallel ? Or other types? Maby some BG n/nx in superE config.

Changed it to 8volt on the tda section now. With IV at 1k and ref at 667ohms (1200 and 1500 paralleled) Running two 1543s in parallell.
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Old 26th October 2006, 11:13 PM   #4
dangus is offline dangus  Canada
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Maybe a transformer with better isolation?
I read someplace that toroids are worse than conventional transformers because they have a wider bandwidth and therefore pass more electrical noise. In case that is relevant.

If the battery solves the problem, could you power the DAC stuff off the 5V from the USB port, using a DC-DC converter followed by some little linear regulators?

There could be some grounding issues since you've got electrical continuity between all the grounds in your audio system through to the computer. I'd be more comfortable with an S/PDIF link to provide electrical isolation - optical or transformer - between the USB output critter and the DAC.
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Old 26th October 2006, 11:26 PM   #5
pipp0r is offline pipp0r  Norway
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The usb bus, is realy noizy not good for audio use, might be workable with some filtering as you suggeste. Im not using usb ground, for the reasons you mention. Only thing powered by the usb on the dac is a light diode, usb ground is not connected.

I'w though of changing the transformer, currently Im using one from Block-Trafo.de model FL6/12

Any suggestions for a more sutable replacement?

Come to think of it there might be an other reason for the problem. Maby my AC mains just is filled with noize, maby its wiered in a wird way or something, and the problem is not with the dac supply and can not be fixed there. So I think Im gonna try a simple filter on the ac mains input of the dac to se if it helps.
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Old 26th October 2006, 11:46 PM   #6
dangus is offline dangus  Canada
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No USB ground? Don't the USB signals need that as a reference? Or do you have the USB signals coupled through transformers or optocouplers?

I'd try whatever transformers are lying around and see what (if anything) makes things better or worse. Your transformer is a "UI" core, which sounds like it should give good isolation (windings presumably on opposite sides, not one over the other like an EI). But there's no pin for grounding the core or an electrostatic shield, which might help things.
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Old 27th October 2006, 12:07 AM   #7
darkfenriz is offline darkfenriz  Poland
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Im not using usb ground
Yes, that's most probably the problem.
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Old 29th January 2007, 06:53 PM   #8
johnthedoctor is offline johnthedoctor  England
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I have the same problem with my AW-D3 usb dac from Audio Workshop.

I use an AT psu to provide 12v to a modded T-Amp and 5v to the TDA 1543. The Burr Brown chip is powered by the usb, a bit too noisy for listening.

When it stops, foobar has to be closed and the usb unplugged before starting again.

Have tried the following and it still stops when the fridge or washing machine turns on/off.

Use the Burr Brown dac so the AT psu only powers the T-Amp.

As above but using a laptop running on battery.

Plug the dac straight into the PC without usb cable.

Any ideas? (I checked the grounds, all there.)
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