M-Audio 192 S/PDIF electrical interference help! - diyAudio
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Old 10th May 2012, 12:09 PM   #1
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Angry M-Audio 192 S/PDIF electrical interference help!

In the time I've owned this card I've used it with 2 motherboards, 2 PSU's, and 3 DAC's. It's currently running in an ASUS P5K motherboard with a Corsair PSU.

Despite the changes, I have always had the same problem - the S/PDIF output goes bad whenever there is a sudden electrical load change in the house, such as lights being turned on. The worst interferance which causes several audio drops over a couple of seconds and sometimes even a nice blast of white noise is turning on fluorescent lights. In each DAC I've tried digital lock is lost, sometimes for half a second, sometimes longer depending on the DAC.

I've checked the ground continuity between the PC, the DAC, and ground and it's good (< 4 ohms). I've tried short and long cables for the S/PDIF. I've played with all the settings for the S/PDIF output of the M-Audio. I even built a basic plug in mains suppressor the plug in next to the PC but that hasn't helped much. I also tried soldering in a 10pf capacitor in series and to ground with the signal. And I tried running one of the DAC's from battery power to completely isolate it from the mains. All to no avail...

The analogue outputs of the M-Audio are completely unaffected.

The S/PDIF output of the M-Audio 192 has galvanic isolation so I can't understand how this could be a grounding issue?

I've just about given up on this card, and recently bought a HDMI audio capable graphics card. But that's turned out no good either as my DAC/Processor takes a few seconds to sync HDMI audio every time I skip tracks!

Anyone got any ideas what I could try next
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Old 10th May 2012, 12:20 PM   #2
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I also had problems with the digital output of the delta 192. I had massive dropouts at 192KHz although non related with the power supply. It turned out that the problem was the cable between the card and the DAC. Possibly too much capacitance. I also noticed while measuring that the amplitude of the SPdif output of the card was well under the standard ~1Volt. Try with a better and shorter cable. Use an L-C filter on the DAC's mains, although i see you used battery power at no use. Is it possible to convert the spdif to toslink and feed the dac with fiber optic cable ?

Last edited by rrrremus; 10th May 2012 at 12:30 PM.
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Old 10th May 2012, 12:46 PM   #3
SY is offline SY  United States
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Quote:
Originally Posted by rrrremus View Post
I also noticed while measuring that the amplitude of the SPdif output of the card was well under the standard ~1Volt.
If you change the "consumer/pro" setting in the control panel, the voltage increases to aes/ebu levels.
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Old 10th May 2012, 05:07 PM   #4
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Currently the S/PDIF cable is 10m long. I made my own cable - RG49 (75 ohm) terminated with RCA's. I'm sure when I tried a shorter cable the problem was still there. I have to move my PC soon so I'll take it to the DAC in the other room and try a few 1m cables again to be sure. Perhaps it could be a cable capacitance issue.

One thing I forgot to mention is it's unaffected by bitrate. The problem is the same througout 44KHz - 192KHz.

I'd like to avoid using TOSlink due to it potentially not sounding as good/not being bit perfect.

I've also tried fiddling with all the S/PDIF settings. Professional mode, emphasis, data type and scms. No joy
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Old 10th May 2012, 05:40 PM   #5
marce is offline marce  United Kingdom
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Thats a long cable, I suspect the card output is not up to driving a cable that long, you are driving a 10m transission line, I am surprised it works at all at that distance.
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Old 10th May 2012, 07:17 PM   #6
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Do you have a scope to probe the digital signal at both ends ?
Do you use ASIO ? You are saying that in analog mode there is no interferece, so then the problem is clearly located within the digital transmission line. Is your ASIO/WDM buffer set high enough ?
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Old 10th May 2012, 09:04 PM   #7
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Quote:
Originally Posted by marce View Post
Thats a long cable, I suspect the card output is not up to driving a cable that long, you are driving a 10m transission line, I am surprised it works at all at that distance.
I know it's longer than ideal. I will swap out the card if I can't fix the issue - perhaps to a card with balanced S/PDIF. Would that be OK for 10m?

Quote:
Originally Posted by rrrremus View Post
Do you have a scope to probe the digital signal at both ends ?
Do you use ASIO ? You are saying that in analog mode there is no interferece, so then the problem is clearly located within the digital transmission line. Is your ASIO/WDM buffer set high enough ?
No scope unfortunately, although I desperately need one these days. I keep looking on ebay for a 2nd hand one but I just get confused with all the possibilities and usually give up!

ASIO/WDM buffer is currently set to 256 samples. I'll test out a larger buffer now. I'm not sure if this is related but the problem is also unaffected by changing to ASIO, WASAPI or Direct Sound.
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Old 10th May 2012, 09:09 PM   #8
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Changing the buffer hasn't helped. I'm going to move the PC to the DAC now and try out some shorter cables...
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Old 11th May 2012, 12:13 AM   #9
wwenze is offline wwenze  Singapore
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Try having the DAC powered by the mains and having the power plugs of both DAC and PC next to each other, if it isn't so already.

And a power filter before both of them may help. Well, I had the same problem and I cascaded two filters to solve the problem. The turn-on of some computer PSUs are much more powerful than fluorescent lamps.
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Old 11th May 2012, 06:10 AM   #10
phofman is offline phofman  Czech Republic
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Quote:
I've checked the ground continuity between the PC, the DAC, and ground and it's good (< 4 ohms)
Look at the soundcard http://audiosgcloak.dyndns.org:500/pic/192card.jpg . That black box in the upper left corner is SPDIF isolation transformer. From google images I cannot tell if that transformer is for the SPDIF input or output, but on other cards I have always seen only output being coupled. Do you see the bracket around the jacks has a room for the ground sleeve to be electrically isolated from the PC ground? http://www.newschoolaudio.com/wp-con...e-192-Flat.jpg

I do not think your PC/DAC grounds should be connected via the SPDIF coax. Most likely your connector is bent and the jack sleeve touches the grounded bracket. And since your DAC is far away, hooked to a different power socket, you are getting a ground loop, disturbing your signal when peak currents occur in the mains (switching the light on).
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