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Do you need linear power supply for DACs?

amirm

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#1
Probably the most asked about question about DACs on audio forums is whether an external, usually linear, power supply improves performance. It just makes sense that it would do that. Doesn't it? Well, let's see if we can figure this out.

I have been kindly loaned a Wyrd4Sound PS-1 power supply for testing. It has replaceable modules that let you configure it for different voltages. The base PS-1 price is USD $499 and includes one regulated output. Additional modules cost $100. The unit I have has three modules in it. Two are 9 volt and one is 15 volt. Sadly, I see no regulatory and safety certification on the PS-1.

I was also kindly loaned an Sbooster BOTW ECO years ago so I thought I test it too. It costs $399 and comes in many variations. Sbooster provides OEM products to many companies and does proper engineering as far as safety standards.

For switching power supply I compared the one that comes with Topping DX3 Pro. Topping also has a strong commitment to safety and certification so the supply comes with such. Here is the whole contraption:

Do you need an external power supply for dac.jpg

Note that this is a long term project and I hope to improve and refine the tests. So consider this "draft 1."

Let's get into some measurements, shall we?

DAC Measurements
As a rule, I am not a fan of showing raw power supply measurements although I will be showing that toward the end. What is most important is whether the signal coming out of a DAC is improved with an aftermarket power supply. After all, those are the waveforms we hear. We don't listen to power supply wires. The impact of power supply noise is very indirect as the DAC usually performs secondary filter and re-regulation. And its circuits may be designed to have high rejection of power supply noise and ripple (called PSRR).

I thought I start my testing with Topping D50. It is a very good DAC and as it turns out, it has a 5 volt input jack that I could mate with either USB power from my computer, or that of the external linear power supplies. I started the test by powering the D50 with USB and the compared the performance to Sbooster BOTW:

Topping D50 DAC with Sbooster BOTW power supply versus USB Audio Measurements.png


The graph is kind of hard to red. But essentially I am feeding the DAC a 10 kHz tone at 192 kHz sampling. The harmonics of 10 kHz tone are visible at multiples of it so ignore that. Everything else is noise and spurious distortion. We see fair bit of them because I have zoomed way in, setting the top of the graph to -80 dB. Blue is the USB port on my computer which I use for DAC testing. We see that when we switch to Sbooster BOTW power supply, a lot of higher frequency spikes go away. Mind you, the worst case one is at -125 dB and all of these are at frequencies we can't hear. But objectively there is some improvement in "noise."

Next I went to test the PS-1 with the D50 and I realized it didn't have a 5 volt output. Thinking there is a pre-regulator in the D50, I plugged it in anyway. Sadly, the D50 didn't power on, nor did it do so with the other supplies anymore. She has died and gone to DAC heaven. May it rest in peace....

For plan B, I decided to test with Topping DX3 Pro since it takes 15 volt supply which lets me test the PS-1. Unfortunately the Sbooster is only 5 to 6 volts so it is out of the running here. I switched the test conditions around to 12 kHz tone at 96 kHz sampling (told you this is a draft work in progress):

Topping DX3 Pro versus Wyred4Sound PS-1 Power Supply Audio Measurements.png


Nothing is changed really if you compare the two graphs but one thing has gotten worse: there are some noise spikes between 1 and 1.2 Megahertz. Note: that is Megahertz, not Kilohertz. We are way, way outside of audible range but folks always think there are bad things up here so I have decided to show it with this 1 Megahertz bandwidth test. We will come back to these extra tones shortly.

I broke my usual rule of only testing audio signals and connected the output of the power supplies directly to the analyzer. I used a differential input so to keep external noise interference at bay (some probably still getting through). Let's compare the spectrum of noise between Topping's switching power supply and Wyrd4sound PS-1:
Topping DX3 Pro versus Wyred4Sound PS-1 Power Supply Noise Measurements.png


Looking to the left, the PS-1 is clearly much cleaner. What is disappointing is to the right: yes, we see those noise spikes around 1 Mhz just as we did in the output of the DAC! I have no idea what the cause of this would be other than I see a display on the PS-1. Maybe there is a microprocessor running in there at this frequency. It is sad that they did not measure the unit the way I have and found a way to eliminate that.

Let's now overlay the noise spectrum of PS-1 against the Sbooster BOTW:

Sbooster BOTW versus Wyred4Sound PS-1 Power Supply Noise Measurements.png


Sbooster (in green) has somewhat higher noise but none of those spikes at 1 to 1.1 Mhz.

Let's focus down in the audio band and see how the three compare:

Topping DX3 Pro versus Wyred4Sound PS-1 Power Supply Noise Audio Band Measurements.png


The general noise level of the PS-1 is the best. We do see a spray of spikes though which I suspect are mains frequency leakage. Sbooster has a smooth spectrum that falls in between. Topping power supply is the worst but again, look at the vertical scale: the highest noise spike is at -85 dB. No wonder none of this matters when we look at the output of the DAC.

Conclusions
It is clear that whether you use the USB power, or the supplied switching power supply, there is absolutely no audible improvement in the output of the DAC with linear power supplies. One can help himself believe otherwise by looking at the noise spectrum alone as I have shown in the last graph. But again, we don't listen to power supply wires. Those waveforms go through filtering stages even in cheapest DACs.

If you do want to get a linear power supply, my strong recommendation is to get it from a company that understands safety and has regulatory certification. In that regard, my recommendation would be for the Sbooster BOTW over Wyrd4Sound PS-1. It is also $100 cheaper.

------------
As always, questions, comments, recommendations, etc. are welcome.

I used a ton of electricity for this testing. So please donate some money so that I can pay my bill at the end of the month:
Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
 

ripvw

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#4
Benchmark make a pretty good case FOR switching power supplies. My old DAC1 had a linear supply but the DAC2 and later have switching supplies as does their amp:

https://benchmarkmedia.com/blogs/ap...audio-myth-switching-power-supplies-are-noisy

this second related link talks about the benefit of star quad cables - Benchmark likes Canare better than Mogami:

https://benchmarkmedia.com/blogs/ap...-the-importance-of-star-quad-microphone-cable

of course, most of us are not working near microphones so a lot of this is likely inaudible...
 

trl

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#5
Thank you Amir for these measurements. I always get late to the office in the morning because I need to read your new articles...:).

Wondering if there's a DAC or headamp out there powered from an external SMPS power brick, to replace the SMPS with a Linear PSU(if possible to find one with the same power plug) and see the differences in noise (in-band and out-of-band), but also the jitter.
 

amirm

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#7
Wondering if there's a DAC or headamp out there powered from an external SMPS power brick, to replace the SMPS with a Linear PSU(if possible to find one with the same power plug) and see the differences in noise (in-band and out-of-band), but also the jitter.
I ran my standard jitter test and it showed no difference at all.
 

RayDunzl

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#8

restorer-john

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#9
It is clear that whether you use the USB power, or the supplied switching power supply, there is absolutely no audible improvement in the output of the DAC with linear power supplies.
I don't believe you can draw such a conclusion at this early point, based on such a small sample group and particularly since we have seen over many reviews, significant low level mains related spuriae and harmonics, some of which are more pronounced or less so, depending on the power supply topology.

Several USB powered D/A converters you have tested have benefited from hub-fed power as opposed to port power have they not? An SMPS is arguably less likely to have stronger mains harmonic spurs depending on how well it was designed, but it will gain noise at the other end of the spectrum.

And in terms of reliability, there is no comparison whatsoever when it comes to low power, low cost SMPSs (like the majority of ones used for small desktop devices you review en-masse here) vs an equivalent linear supply.

What about THD/THD+N vs Freq into various loads when run from the different PSU options?
 

solderdude

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#12
These power supplies are all measured in differential mode between the power pins.
That will always be filtered as Amir already stated.
I am not surprised to see any big changes.

But the biggest differences between power supplies is leakage currents. These are the currents that cause groundloops.

Quite easy to measure those as well.

Connect a 100 Ohm resistor between the safety ground and one of the output pins of the power supply (would use the - DC out)
Then measure the voltage across this resistor and you are measuring the practical almost maximum leakage current.
Of course multiple SMPS could increase/alter the total leakage currents in the ground path of audio equipment even more.

One could repeat the measurement with a DAC connected (USB and line-out) and see if it changes.

Well performing SMPS and linear power supplies exist as well as poor performing SMPS and linear power supplies.
 
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#13
I would think we also have to measure the effect of leakage currents at the receiver end (amp input), like I did a while ago.
"Supply sound" mostly is a systems things. Notably with unbalanced connections.
Disturbance of a device measured in isolation (not easy with unbalanced interconnects, btw) is the baseline, of course.
A truly significant evaluation of the DUT (the DAC in question) would include to measure its PSRR, both at LF differential (DC to100kHz) and at RF where it is more a common-mode demodulation test, which can be extremely revealing.

I know this is outside of your gear's capabilities (the RF thing at any rate) but without this data, I would hesitate to call the choice of supply for a specific device irrelevant, making no audible change. We only know that in that single specific test you choose to perform the measured changes are benign.

EDIT: I see I crossposted with SolderDude on the leakage topic.
 
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#14
Although ultrasonic cannot be detected by human, but these signal will be passed to amplifier and then loudspeaker, would they have any negative effect on the final signal?

At the end of the day, we don't hear the waveforms the DAC produced. We hear the waveforms loudspeaker produce. We don't know whether these ultrasonic peaks will affect speaker yet.
 

JJB70

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#15
Well performing SMPS and linear power supplies exist as well as poor performing SMPS and linear power supplies.
This, as with everything I think execution is crucial. As with so many things the question isn't so much whether X is better or worse than Y, but has X been well implemented. I see no reason why a switching supply cannot be perfectly adequate, there is plenty of evidence of high performing gear which uses switching supplies but as with anything it can be done badly.
 
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#17
Well, my experience with D50 and cheap wall power supply: cheap psu gives audible buzz to my speakers even when it's not connected to D50, it is enough to plug it in to wall (Supra MD06 mains block). Powerbanks psu doesn't give that buzz or obviously powerbank itself.

So, there are factors outside of these measurements that may cause audible differences. BUT then again as measured above, if i ignore that buzz there is no audible difference in SQ between powerbank and cheap psu.
 

MZKM

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#18
Do you have any $100 or cheaper DACs you can test? I know it would be silly to pay so much for one of these linear power supplies instead of just buying a higher end DAC, but still.

For the slightly lower noise for the D50, would that have any meaningful impact on its SINAD rating?
 

Krunok

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#20
May I know where can I read more about it?
Google it, it's not hard to find. But for what I remember even the fancy beryllium dome tweeters like the ones in Salon 2 don't go over 30kHz, so everything you throw at them above that converts to heat.
 
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