The outer diameter 5.5mm (-) and the inner diameter 2.1mm (+).
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When I looked at the Teddy Pardo website various sizes could be chosen. I was happy to see they also had a 9 volt version. I may order one of those…
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Can you explain why you’d chose the 9V version over one of the other options available?
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To my ear the Matrix sounds considerably better when externally powered at 9 volts. In my personal experience it sounds lifeless and dull at 7 volts. I have not tried 6 volts.
My personal belief.
(Cue naysayers)
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Cued! The Matrix SPDIF 2 uses voltage regulation internally and reduces voltage above 6v down to something under 6v. So the 9v never reaches the circuitry that is responsible for the digital to digital conversion. Also, that voltage regulation circuity has to do more work when reducing 9v than 7v and that work can only have no effect or hurt sound quality. It can’t improve sound quality.
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Well, the only thing those extra volts could buy you here is heat and noise. Neither of which improve the sound…so either you like noise or you are succumbing to expectation bias.
I’m using 9 volts because it sounds better to me. I really don’t care about the other gobbledygook. 
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This implies 9V has a higher current capacity, which – during moments of high activity, can better support delivery of the bits. Hard to know without studying the circuitry, so biases either way.
Note that the Matrix SPDIF 2 uses voltage regulators and is listed as supporting 6v to 9v. Regardless of the input voltage in the 6v to 9v range, that voltage is regulated down to 5v BEFORE it reaches any of the circuitry that does the digital to digital conversion. In other words, using a 9v power supply does not mean the DDC is running on 9v. It is running on the voltage from the voltage regulation circuit which is fixed. So there is no “higher current capacity”.
Yang, from Matrix, is on record as saying using less voltage is better. He recommended 6v but said 7v is better than 9v. Anything above 9v might damage the device.
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Let’s not forget one of my earlier observations: a power supply that I was using set on 9V delivered more than 9V. This exceeds the manufacturer’s specs and would invalidate any warranty.
I run the Matrix at 7V to avoid that possibility.
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I don’t recall my electronics too well, but the regulators would be holding V constant. By the equation, holding R constant and V constant, what you have is a variance in the current through the circuit.
I.e. a higher voltage input V for the same R means current I is higher through the circuit.
Perhaps the Matrix has current regulators as well.
Am I missing something?
the circuit will pull as much current as it needs in either case. driving the regulators with higher voltage does not guarantee higher current availability, just more heat. there may be other reasons why the higher voltage improves the sound for some, I’ve learned not to doubt what others hear on this forum, but it’s not extra current availability, that would depend solely on the current available from the psu itself, which is not directly related to the voltage it drives at.
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It’s not necessarily the fact that it is 9V over 7V that makes the matrix sound better. There is something else at play which is not fully understood by anyone. For example my LPS-1 sounded much better when outputting 9V to the matrix, but is that the PSU design that outputs less noise at 9V? Or maybe more noise that sounds better to me. i.e it may be nothing to do with the matrix but the psu being used. Whatever it is it’s due to changes in noise patterns that the DS is sensitive to.
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FWIW, here is my recent correspondence with Matrix retailer Moon Audio regarding a 9v switching power supply it sells specifically for the X-SPDIF:
"Sorry for the confusion as the info here did not get transferred to the 2 product pages just the main page for the power supply.
Matrix does not produce a power supply. There is a potential for a linear power supply down the road but I would image it being in the $4-600 range. As these are more expansive to produce. Matrix Audio recommend the product we are selling for the US market as an alternative to using the 5v bus power of the computer which tends to be noisy and under powered. This supply removes the computer from the equation.
So to answer your questions there are no Matrix power supply options that they make in house."
The piece in question is labeled as a “Medical Power Supply,” whatever that means, and produces more gain in my system between a Nucleus Rev B and my DSJr than 5v USB bus power did.
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I think medical psus tend to be made from better components and have longer mtbf
One would hope.
In my setup and to my ears, running the Matrix at 9v sounds much better than 7v. Since I get the Matrix mainly to improve SQ, I don’t want to compromise SQ and not running it at 9v.
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1+ on that. The Matrix may not last as long, but let’s face it, audio devices are pretty short lived, anyway. So, get the max out of them while they last.
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Can you please confirm what psu you use when saying 9v sounds better to you than 7v
That’s rated for 2A.
It’s curious how everyone’s talking about Voltage, but isn’t talking about Current?
I would think that current also matters in ensuring adequate power to the circuits to do their work. After all, we don’t run 20A circuits and buy bigger PowerPlants because we necessarily need the power. It’s the “headroom” in the power source, PP and power amplifiers that creates for a more dynamic listening experience.
So… for all of you with external power supplies, can you take a look and fill in this survey for all the combinations you’ve tried?
Device Name (i.e. ifi, etc.) – Type (i.e. LPS, SMPS, etc.) – Voltage (i.e. 5v, 9v) – Current (i.e. 1A, 2A) – Sound characteristic (i.e. bad, good, better, open, flat, etc.)