@Elk The regulator does NOT pass on more voltage to the circuits when the supplied voltage is higher. The ONLY possible effects of more voltage is more heat from the regulator and more electrical noise passed on to the circuits. Neither of those possibilities are positives.
@speed-racer, I’ve known bullies all my life and you are showing the signs of being another one. You have repeatedly made your view. Enough now.
Stop bullying me…
I new you would say that 
it’s just you keep saying the same thing. There is clearly something else going on that you (and everyone else) does not understand.
So there is something else going on that even the manufacturer does not understand?
I know what is going on: it is expectation bias. People want to hear a difference so they do.
Look, I tried 6v, 7v, and 9v. I heard no difference between them. Of course, I didn’t expect to hear a difference so you could say I have expectation bias as well. The difference is the facts on the ground support my expectations.
A quality voltage regulation circuit receiving a higher voltage is not going to pass on more noise but it is going to get hotter. So, the sound will not change but the regulator will have a shorter life. Again, this is also what the manufacturer said.
There is enough subjective crap to deal with in the audio world without having to add bogus stuff to the mix.
Yes, you have written this many times. We understand this is your belief.
Again, if others find it works better at other voltages, it works better. As previously recognized, your experience may differ.
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The situation is a little more complicated. LDO’s do a better job with more headroom but those differences are smaller than the differences that depend on input caps, output caps, current, etc. Still it matters and better regulators will have graphs:
Headroom is the voltage above the nominal output voltage. Older regulators needed 1.5V to 2.0V or dropout voltage (minimum headroom voltage). Newer (expensive) regulators can have very small dropout voltages, e.g. 0.083V. But tho a regulator might have a small speced dropout voltage a little more headroom can help.
On the other hand a linear voltage regulator has to convert extra voltage to heat. So any extra headroom voltage becomes heat.
If, for example, the Matrix needs 300mA, then raising the input voltage from 6V to 9V will add 3V * 0.3A = 0.9W more power dissipation which will becomes heat. That 0.9W won’t add a lot of heat to the whole box (tho 9V instead of 6V will add 50% more heat to the box as a whole.) But that heat will affect nearby components (like the filtering caps). A typical higher power capable regulator may have a thermal resistance from it’s core to still air of 45 degrees C / Watt. so 0.9W causes a 40.5 degrees C (which is 72.9 F) rise in temperature.
Each 10 degrees C rise in temperature halves the life of aluminum electrolytic capacitors, so 40.5 degrees C will cut the life of any filtering capacitors near the regulator by a factor of 16.
0.3A for the matrix is a wild guess, but you get the idea. (It won’t be that bad, but I wanted to show the concepts.)
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Of course, it may not be the matrix at all but the psu being used. It may be that variable output psu being used may have different noise patterns at different output voltages which makes 9v more pleasant for that particular psu
Yep, I should have said that too. (Actually I did say that multiple times earlier in the thread where I also talked about the possible downsides of too much voltage.)
Maybe the extra heat is what makes it better for some systems.
Kind of like a bright red exhaust system makes the trip a lot more fun but does shorten the life of the engine considerably 
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All other things being equal, can you come up with a plausible explanation as to how the Matrix would sound better using a 9v supply vs a 7v supply? Assume the 9v and 7v supplies have equally good noise characteristics.
I just gave one. Regulators do better with a little more than the minimum headroom. But more than a volt or two of extra headroom isn’t useful for most regulators. That’s why up higher I suggested that 7V might be better than 6V. On the other hand getting near or over the speced maximum will certainly shorten the life of the device. Cooler is simply better for electrolytic cap life.
As chris5 mentioned the differences caused by external factors are likely to be what many are hearing. Different shielding of the power umbilical from different supplies or supplies that function better at higher output voltages (not unexpected for many circuits) come immediately to mind. Personally I’d be looking at 7V supplies that sound best instead of looking at supplies that sound best at 9V.
Note that I’m basically agreeing with you, except your false statement that more voltage doesn’t help. Some more certainly does help, too much more is bad for other reasons.
Here’s another graph of a voltage regulator built with a slightly different topology:
Different people may be sensitive to different frequencies of interference (note that these differences are pretty small in actuality.)
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As I said, all other things being equal. Of course the quality of the power supply at each voltage matters.
Also, since the Matrix only need 5v, a 7v supply offers plenty of headroom for a modern quality LDO as your chart shows. I don’t see 9v being demonstrably better than 7v based on the graph. Even 1v difference is really more than enough and I doubt anyone could hear the difference between 6v and 7v or 7v and 9v. The levels or rejection just aren’t that much different.
I recently noticed that my Matrix connecting to a 9V SBooster is warm to the touch when it’s in idle; after the music is playing for a few mins, it cools down considerably - almost as if without the PSU. The point is that if you are concerned with the extra heat at 9V but like the sound, shut off the PSU when not using the Matrix.
Not being a tech i just follow my ears. Playing with the different LPS 1.2 loads in my -quite resolving- system was not really worth it SQ-wise. But right after i plugged the Farad i was quite shocked. In my experience real gain in sound quality using the Matrix must be sought in the actual quality delivered by the linear power supply.
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Thanks for your explanations on regulators, @tedsmith. It looks like this discussion on over-voltage is finally turning a corner. I supplied 6v to my Matrix to give it headroom; but without knowing the facts you just shared. I guess it was a good guess
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Ears rule.
As Ted notes above, different people may be sensitive to different things. I am continually amazed with what fellow forum members notice, can hear, and report on.
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I have no idea which voltage is ideal, but I chose a 7V Teddy Pardo LPS because it falls smack dab in the middle of the 5V-9V that Matrix recommends for the X-SPDIF 2 and that makes sense to me.
I run my Matrix at 7V as well, as I couldn’t tell any noticeable difference between 5V, 7V & 9V, although I use the Uptone LPS1.2 with mine. (the Matrix runs fairly cool at 7V, but the Uptone LPS 1.2 runs very hot; is this normal?)
I will try it unplugged. The idea of it was I would go out of the p10 and get some value there.
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