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In the Forum: Audio Discussions
In the Thread: It’s mad, mad, mad... electricity.

Post Subject: Behavior when AC is from PP onlyPosted by Lx_ on: 1/6/2011

I have modified my system to make sure it has a single dependency on AC. Until now, everything was plugged to PP except one regulated PS for the PC feeding the DAC. This PS in not on PP because it generates lots of noise, and plugging it to PP injects noise into other components. When plugged behind PP, noise still carries through but PP somehow manages to shield some of it. So it was possible that the differences in sound I could hear were not due to PP performance but because of AC noise (e.g. PP noise) getting through the PC PS and back into the digital signal.

I have recently ordered LFP batteries to power the clock on the sound card. A simple alkaline already gives better results than the regulated PS, and the LFP seems to be at least on par (I have yet to make direct comparison). Anyway, the battery packs have enough capacity to feed the PC for around 30 minutes. This makes it possible to remove the noisy PS altogether, and the PC is now disconnected from utility AC (it has another PS for LCD and SSD, but that is plugged to PP).

Now the entire system is connected to utility AC only through PP. This means it is very easy to test how it reacts to incoming AC:

"AC": normal PP operation, running from utility AC
"grounded battery": I can switch to battery mode to disconnect incoming AC hot and neutral, but leaving utility ground connected
"pure battery": I can unplug the PP from mains to disconnect incoming AC completely, including ground

Grounded battery is way better than AC. At the macro level, sound is more relaxed and the phrasing in the artist's play is more apparent. At the micro level, timbres are more accurate, there is more detail and the various instruments and voices all work in better rhythm.

Pure battery is also better than grounded battery. How much better? Well, it depends on the amount of ground noise. If I have several appliances on (fridge, heaters, I also tried the noisy PC PS), then a lot better. If all appliances are off, there still is a difference but minor (maybe there is noise from other appartments).

What can we infer from all this?

PP output is not completely isolated from input; this is true for ground as well as hot/neutral
Either PP lets input AC noise through, or there is a problem with the battery charging circuit generating noise on the output, or something entirely different. But noise gets through when not on battery. APS should be able to fix this.
Ground noise is an issue for which I have no acceptable solution at the moment. I think APS will not work on this, they say PP will not solve ground issues. Lifting ground is OK for a simple test but I do not want to operate like this. I will have to try using a filter on incoming AC. Otherwise I will have to live with whatever appliance noise there is.

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