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Computer Audio Asylum Music servers and other computer based digital audio technologies. |
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In Reply to: how does this relate too my setup? posted by hfavandepas on October 14, 2014 at 12:12:55:
Sorry for taking so long to reply. Let's review so we don't argue in circles.
You have confirmed that your PC is isolated from the rest of your audio system via use of a Toslink cable without any other connection, so we can rule out a ground loop through your audio components as a potential source of the problem.
You previously said that your system sounded better with all components plugged into your dedicated audio spur than it did when only the DAC and speakers were plugged into the dedicated spur and the PC and TV were plugged into other spurs. Further, you said that the TV has an ungrounded mains plug and therefore it's grounding won't be affected by which mains spur you plug it into.
Based on that information, I had previously concluded that one of the following two things could be happening:
1. Putting the PC on the kitchen mains spur is causing degradation of the digital output from your PC, which the Lavry is not able to fully mitigate. My guess was that your PC is affected by the quality of the power and/or ground provided by the mains spur.
2. Plugging the additional equipment into your dedicated audio spur is somehow positively affecting the quality of power or ground delivered to your DAC or speakers. This hypothesis seems very unlikely. I would expect that there would be no effect or a negative effect on audio components on the same spur.
In your last post, you revised the problem statement and seemed to narrow the problem down to an interaction between the PC and TV. If I understand you correctly, you observed a difference when the TV and PC are on the same spur vs. different spurs. But since the TV is not grounded through the mains spur, it shouldn't matter which spur you plug the TV into.
I am still not convinced that the difference you observed is caused by a ground loop. We can rule out the traditional pin 1 problem where ground loop currents are flowing through an audio circuit. But because we don't know whether the TV has transformer isolated connections for the coax antenna/cable inputs, we can't yet rule out a ground loop between the PC and TV. However, a ground loop doesn't seem to be the best fit for your observations. It does not explain why putting the PC and TV on the same spur results in an improvement. Also, if a ground loop exists, it enters the PC via the HDMI connection into the video card, and the sound card ground is not in that loop.
Here is what I suggest for further experimentation:
1. First revert to your original configuration in which the sound was degraded
2. While playing music, disconnect the coax cable connection to the TV and see if sound quality improves. If sound quality improves, then it's likely that the coax cable shield is not isolated from the circuit ground in the TV, and it's allowing noise to be introduced through a coax->TV ground->HDMI shield->PC ground path. If that is the source of the problem, I suggest inserting a ground isolation transformer in the coax cabling close to where it enters the TV. Alternatively, you could try adding a coax grounding block there with a short lead to the TV and then connect the grounding block back to the equipment ground via a low impedance connection (e.g. a ground wire connected to a mains plug which is plugged into your dedicated audio spur) or connect the grounding block to the PC chassis.
3. If sound quality did not improve after disconnecting the coax cable feed, then disconnect the HDMI cable from the TV. The HDMI cable contains +5V and ground wires because a few of the signal wires are single ended. If sound quality improves after disconnecting the HDMI cable, then it could be that the ground connection through the HDMI cable is not sufficiently low impedance, which could be remedied with a supplemental ground wire. Or it could be that the +5V line in the HDMI cable is driving a noisy load in the TV, in which case you might try adding an HDMI amplifier to better isolate the PC from the TV, or replace the TV.
4. If disconnecting the HDMI cable from the TV did not improve the sound, then the problem is isolated to the PC mains connection. So just connect it to the dedicated audio spur and/or add a power line filter.
Here is a good reference on audio grounding:
http://www.jensen-transformers.com/an/generic%20seminar.pdf
By the way, I absolutely disagree that connecting the circuit ground to the chassis is a design error. On the contrary, it is a best practice and originated in instrumentation where EMI and RFI suppression is particularly important. Also, when pro audio designers say that consumer audio equipment is flawed by design, I think they are referring to the unbalanced connections.
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Follow Ups
- RE: how does this relate too my setup? - Dave_K 08:41:46 10/21/14 (0)
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