time for the monkey wrench
I was on tour in Paris a few years back. We play big concert halls so the PA guys are pretty much as good as you can get.
The sound guy gives me a ($150) power cable to try. I figure it can't hurt. After sound check I a/b'd it with my cord. I was kindof shocked---it sounded noticeably better. It was the beginning of the tour and he said I could keep it until the end of the tour as we finished in Paris.
One day I spent two hours in the concert hall a/b ing the cable with a regular one. Bass impact was more powerful---the envelope was noticeably better. Not super profound but not subtle either. I bought it.
It has a small plastic box in line with some electronics in it. Supposedly it filters out junk. Maybe I'll send it to some expert here to see what's inside.
It is used extensively in recording studios in France. I don't have it handy---I actually don't use it regularly----too expensive! I'll find the name and post it.
Still, this is not surprising. I have a reasonable explanation for you. Just like in the stereo store, it is still voltage drop. You just have to know where to look.
Does a system for a big concert hall draw more current than my son's 15 Watt practice amp? Yes, a lot more. Then why should they use the same power cable?
This is just a generalization, but preamps are regulated, at least with a Zener. However, power amps aren't. They want to put out whatever the line voltage gives them. And what is that line voltage? In the US, is it 115 VAC, or is it 117, or is it 120, or 125? Are we having a brown out?
What does all of that do to your rail voltages?
And that was Paris. Was it 220 or 230. Is 220 really 215 or 240. Measure everything and you will figure it out.
I would bet that your rails changed by a few volts when you changed power cords. Double blind testing isn't necessary, just a volt meter on the rails. And a musician with a trained ear would detect that.
A voltage drop in the cable will affect unregulated rail voltage. End of story. Pick up a Newark catalog for reasonable priced cables.