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Matthias of RME on external power supplies!

JJB70

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#4
Spending $$$$$$$$$$$$$$$$'s on expensive power conditioning is a very lucrative craze for those companies pushing power supplies, it's in the same sort of snake oil bucket as cables, magic stones and green highlighter pens IMO.
 
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#6
Hilarious indeed. But, while I liked the visual scope example, I think it misses the boat for the target audience.

The believer could then argue that expensive USB cable X delivers better square waves than standard USB cable Y and be somewhat correct in some cases. The key is, ofc, that it does not matter and that at a lower level, the square wave could be clown hat shaped and it still wouldn't matter provided that D+ is above 2.8 V and D- is below 0.3V or vice versa (as an example, link type dependent ofc) at the correct moment without even going into checksum issues.

And, obviously, if a digital cable was doing something on the data stream that opened the scene or gave more chest to voices, the clever thing to do would be to replicate the effect in software which would allow almost infinite savings on the BOM of the cable. ;)
 

Jaimo

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#7
Too bad these flat-earthers destroy any objective discussion around cables. It's pretty clear that there are measurable performance differences between various analog and digital cables and there's still room for improvement in measurement technology.

Having or developing the ability to hear the difference is an entirely different conversation but this should not hinder efforts to measure or build better cables.
 

Blumlein 88

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#8
Too bad these flat-earthers destroy any objective discussion around cables. It's pretty clear that there are measurable performance differences between various analog and digital cables and there's still room for improvement in measurement technology.

Having or developing the ability to hear the difference is an entirely different conversation but this should not hinder efforts to measure or build better cables.
So we have our own irony of the flat Earth.

One can develop the ability to hear what isn't there.
 

Jaimo

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#9
And I might add, develop the ability to deny that what is there, isn't there...tape hiss, pops and clicks, cellphone drop-outs etc.
 
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#10
The stock wallwart SMPS packed with the Adi-2 and Adi-2 Pro (and other RME units) is somewhat substandard, and RME knows this.

While the output voltage itself is not the problem (it *is* spikey and ripple-laden, but the internal PSU concept of those interfaces handles this with no problem), the mains leakage current is as bad as it gets, it's a bog-standard lowest-cost SMPS with 1nF or so of "EMC"-capacitance from secondary to primary (and the primary is rectified mains, hence the current isn't a benign 50Hz-only sinusoid).

The resulting balancing current which return via PE/mains of the connected components (amp, source/PC) can induce considerable noise when lesser quality RCA cables are used, notably longer ones. Voltage drop along the shield, both R*i and L*di/dt components. A systems EMC/SigInt issue, of course, the interfaces themselves are perfectly fine. A low leakage medical grade, well-filtered SMPS would be in order to solve this. I personally break the current loop by inserting a 12V/12V medical D/DC-converter with only 20pF coupling capacitance, balancing current went down 30dB easily.

The second issue with the stock supply is that it is mechanically fragile, the DC cable and its strain relief is not durable at all and will fail quickly when used/moved a lot. In a permanent home or studio install this is acceptable but it is certainly not the level of industrial quality that I would like to see here, compromising those otherwise very well-made and rugged products.
 

Purité Audio

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#11
Do you have some measurements taken from the dac’s output which show the ’improvent’?
Keith
 

Pluto

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#12
It's funny and bothersome at the same time
The most disturbing aspect to this, I find, is the total failure of the “foo” brigade to appreciate that any damage a cable or power supply could possibly inflict upon a digital system is highly unlikely to have a direct correlation with any of the traditional audiophile yardsticks such as ‘spaciousness’, ‘musicality’, ‘got my foot tapping’, ‘stopped my bunion itching’ etc. etc.

If there is anything that working with digital audio since 1980 has taught me, it is that the most common symptom of any kind of issue with the signal is that you hear nothing at all.

The second most common issue is that you hear nothing interspersed with chunks of something that might resemble the audio you think you should be hearing.

The third most common issue is that you hear recognizable audio with the addition of clicks.

Given the amount of DSP power required to adjust the degree of ‘spaciousness’ in the sound, how on earth can anyone believe that it is within the capacity of a cable to make such a discreet change to the sound quality!
 

Music1969

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#14
The stock wallwart SMPS packed with the Adi-2 and Adi-2 Pro (and other RME units) is somewhat substandard, and RME knows this.

While the output voltage itself is not the problem (it *is* spikey and ripple-laden, but the internal PSU concept of those interfaces handles this with no problem), the mains leakage current is as bad as it gets, it's a bog-standard lowest-cost SMPS with 1nF or so of "EMC"-capacitance from secondary to primary (and the primary is rectified mains, hence the current isn't a benign 50Hz-only sinusoid).

The resulting balancing current which return via PE/mains of the connected components (amp, source/PC) can induce considerable noise when lesser quality RCA cables are used, notably longer ones. Voltage drop along the shield, both R*i and L*di/dt components. A systems EMC/SigInt issue, of course, the interfaces themselves are perfectly fine. A low leakage medical grade, well-filtered SMPS would be in order to solve this. I personally break the current loop by inserting a 12V/12V medical D/DC-converter with only 20pF coupling capacitance, balancing current went down 30dB easily.

The second issue with the stock supply is that it is mechanically fragile, the DC cable and its strain relief is not durable at all and will fail quickly when used/moved a lot. In a permanent home or studio install this is acceptable but it is certainly not the level of industrial quality that I would like to see here, compromising those otherwise very well-made and rugged products.
But @amirm measured this and specifically commented about it...

"Note also freedom of low-frequency noise below 1 kHz, indicating exceptionally clean supply (external wall-wart is switching by the way)."

Where does the effects of AC leakage currents show up?

Screen Shot 2019-02-12 at 12.19.29 am.png
 
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#16
As I wrote earlier, the DAC is fine, the error is not seen directly at the DAC output. The error develops along the shield resistance/impedance of any unbalanced cable whenever the full SMPS leakage current is allowed to flow through that shield. The problem is that the impedance to mains is low and the voltage is heavily distorted, rectified mains, making the current much more aggressive than that of traditional linear or specialist low-leakage SMPS supplies.

Rather than writing a lengthy post here, I made a PDF document where I show the setup and the measured results of this kind of errors which can easily sneak into a measurement or listening setups with unbalanced interconncects.
It also shows the Adi-2 Pro FS is excellent by itself and it's easy to compromise its performance in a specific setup just by using the wrong interconnect plus supply combination.

EDIT: I updated the document to show a diagram of the test setup, and added minor clarifications.
 

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#17
@Purité Audio & @SIY, any comments?

As far as one can tell from the condensed area left of 1kHz in the plot from post #14, the SCIN is close to nonexistent with a balanced cable, this is also what I see when I re-run my test with balanced cable with all pins shorted together at the far end of the cable. This perfectly fits the expectation when using a good balanced cable even with that noisy remote SMPS supply.

But when an unbalanced cable is used (or must be used because there are no XLR outs) and the balancing current from a cheap SMPS wallwart is allowed to flow through the shield the degradation is very easily measured and it's not completely unlikely that it does matter for perception as well when sufficient levels of noise are developped.

That's why I disagree to MC's statement in post #31 of the linked thread in the RME forum. The Adi-2 / Adi-2 Pro are very well made and free of supply related errors but their power supplies can easily spoil the perfomance in a system unknowningly and that's why users comments like "it sounds better with XLR" should not automatically be treated as bogus.

I might extend my measurements (like adding the exact cable specs, etc, testing different cable, test also against quasi-floating source which still can result in a lot of disturbance , provide a real-world example -- measuring noise floor of non-floating preamp with only unbalanced output, etc etc) and present this at the RME forum as well. RME is known to treat user input respectfully when one has data to back up. And as I said, some engineers at RME (actually IMM staff, which develop and build a lot of RME hardware) have confirmed they are aware about the leakage current issues of their stock supply. We can even find some posts by MC where he states in certain conditions he would suggest use of a linear supply with more benign leakage to solve some buzzing issues in the off state of the interface....
 

Theo

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#18
Like the guy said on the RME forum : "The sound is much analogue and softer. It's deeper and the scene is widero_O". Obviously, no one knows what reality is...:mad: That's why I'll never fly to Tahiti (I'm not even sure it exists: pictures and hearsay don't prove anything), I may fall when reaching earth's edge.:eek: And by the way, Americans never went to the moon, they would have fallen too...:facepalm:
 

Music1969

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#20
RME is known to treat user input respectfully when one has data to back up. And as I said, some engineers at RME (actually IMM staff, which develop and build a lot of RME hardware) have confirmed they are aware about the leakage current issues of their stock supply. We can even find some posts by MC where he states in certain conditions he would suggest use of a linear supply with more benign leakage to solve some buzzing issues in the off state of the interface....
Good idea. I applaud you on trying to investigate in a methodical way.

As you know, SMPS's can be designed to have lower AC leakage than linear PSU's. Rob Watts (Chord) and Andrew Mason (THX Engineer) have written about this on Head-Fi and here, respectively.

Linear PSU is not an automatic guarantee to have lower AC leakage than SMPS's.

But maybe the one you are testing has higher AC leakage than they'd like.

Worth sending your findings to RME Engineers.
 
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