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Do you need linear power supply for DACs?

Superdad

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I originally wanted to stress test the supplies with it but then worried it could damage them so I did not go there.

Both of those units have overcurrent protection. They absolutely should not fail when run at their rated output current.
That said, I have benched a whole bunch of Chinese LPS units (Zerozone, Studer, etc.) and published photo proof of them not making it past half their ratings. Still, all that happened is the output voltage dropped precipitously.
 

Ron Texas

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Linear power supply, heck. Linear accelerator, go!
 
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amirm

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I know that to you, nearly everything is about measuring noise (though you are not equipped to properly directly measure PS noise down into the µV range), but the much more important performance figures of merit for power supplies used for digital components is output impedance, plotted broadband--from about 5Hz to 700KHz. Of course performing that measurement is rarely very straightforward either. :cool:
That is how you sell power supply to audiophiles with misinformation. Not how the real world turns.

Every one of these DACs has internal decoupling and reservoir capacitors. These substantially lower the impedance that the internal electronics in a DAC see. Indeed whatever low impedance the external power supply has will get destroyed by the time it goes through wire, connectors, etc. This is why these supplies don't show an improvement in actual audio devices. The internal design of the DAC obviates the need for them.

You don't even seem to have read the review with that comment regarding noise. What I showed were spectrum of such noise:

index.php


I did not quote single number noise figures as power suppliers use to mislead. Such numbers have no value whatsoever. For example, if noise and spurs are above audible frequency as they are in above graph, who cares what they are? We need to see the spectrum to know whether they are, or not audible.

And on that front, the only spectrum we care about is what comes out of our audio devices. We absolutely do not care what is on the power supply wire as no one connects that to their amplifier and speakers.

This kind of misinformation campaign doesn't belong in this forum.
 

johan

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Hi Amir

on both tested units I notice spikes at main frequency , -110 and -130. Can you confirm ? Also I assume you tested at 1A ?
 

trl

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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.

The ultrasonics, if generated by a poorly designed SMPS (boost/buck converters or regular SMPS PSU) might have lower harmonics that could get down to the audio spectrum. If switching freq is let's say 150 KHz, then 4th (18750 Hz) and 5th harmonics (9375 Hz) could get audible, but this is easy to intercept with ARTA and soundcard or with a scope. I found this scenario to a DAC and the headphone amplifier picked up those high freqs into the headphones. However, on the speakers I couldn't get any noises, just on headphones.

If a DAC has ultrasonic freqs, these will get injected into the connected amplifier and, depending on it's input stage low-pass filter, might get injected into the output stage or not. If will get injected, that the output stage will heat up a little bit more while pausing the music. Also, these ultrasonic freqs might cause pre or post ringings and, why not, oscillations on the driver transistors or to the output stage itself.

Of course, what I'm speaking here would be sort of a worst-case scenario, because usually amplifiers are using LPF at least on the input stage, if not on the output stage as well (RC, LC or RLC network to prevent oscillations).
 
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amirm

amirm

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Hi Amir

on both tested units I notice spikes at main frequency , -110 and -130. Can you confirm ? Also I assume you tested at 1A ?
Hi Johan. Sorry but I have lost context. :) What are we talking about?
 

johan

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In your "audioband spectrum of noise " for Sbooster and LP1 , what load did you use ? My question is at how many A the noise figures were taken .
 

solderdude

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From the test:
Sbooster was driving D50 which acc. to data found on the web is 0.21A @ 5V
PS1 was feeding DX3Pro = 3.3W in idle so at 15V = 0.22A

So... looks like 0.2A
 
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amirm

amirm

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So sorry for your D50 :(
Yeh, it was a sad thing. We are holding a funeral for it on March 31. Burial will be in our backyard. In its honor, we will be playing music with another Topping DAC.

Anyone wanting to help defray the costs of the funeral, should donate funds fo the forum.
 

Hypnotoad

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I was getting annoyed with the silly connector needed for the SMPS for my D30 DAC, it comes with a U.S. two pronged plug and you need an adapter for Australian sockets. The one that came with it was useless and I found another one at home that worked a lot better. But now even that had to be fiddled with to get it to connect properly, I was listening earlier then heard a click and a dramatic drop in volume. Hmmmm did something blow up? Nope it was the PSU disconnecting, so it must power the op amp in the analog section and the USB 5v must power the rest as I still had some sound but both lights were off on the D30.

Then I had a thought, we had a Netgear router/modem left over from our cable internet, its SMPS is rated at 2.5amps and has the proper connection for the Topping and the Australian plug on it, its output was 12vdc not 15vdc, so I gave it a try and voila it works a treat, no difference in volume or sound quality. Topping needs to address this as many have complained about not having the proper connection for different countries.
 
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amirm

amirm

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Then I had a thought, we had a Netgear router/modem left over from our cable internet, its SMPS is rated at 2.5amps and has the proper connection, its output was 12vdc not 15vdc, so I gave it a try and voila it works a treat, no difference in volume or sound quality. Topping needs to address this as many have complained about not having the proper connection for different countries.
Whenever I throw out a piece of electronics, I keep the power supplies for this occasion. I must have a hundred of them. :)
 

amjosh

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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:


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:

View attachment 23442

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):

View attachment 23443

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:
View attachment 23444

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:

View attachment 23446

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:

View attachment 23447

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).
May the D50 rest in peace!! I am powering it with an apple iPad charger and I think I am going to continue doing it :). Very good analysis that I was waiting for a long time.
 

tensor9

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Doesn't ring a bell right now as far as equipment loaned to me for testing.

Yeah, it's like a $500 high-quality switching PS. I'd love to see some actual number on it, but I don't know anyone who owns one. Wonder if SOtM would loan you one?
 

signalpath

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The main reason I've chosen SMPS over linear in DACs is LF noise (60Hz, 120Hz, etc.). When seeking ultra-low noise floors (preamps, DACs, ADCs), even a tiny bit of stray 120Hz EM noise can become a problem. And as Amirm noted, the non-audio noise (HF) is entirely filtered out by the time it gets to the audio outputs. Even better, put the SMPS outside of the chassis.
 

solderdude

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Some cheap wallwart SMPS still have some 50/60Hz components in their DC output which can easily exceed that of a linear one with regulated output. This is because the rectified mains voltage (using small caps as small and cheap is obligatory in those devices) and some of that is modulated on the high switching frequency and insufficiently filtered out secondary. Again, small caps because of high frequencies and no post regulations.

The better SMPS indeed can be better than linear PS.
 

levimax

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Surprised there is not more talk about batteries, they are a quite, clean, cheap and easy PS solution especially for DIY projects. I use battery power for my pre-amp and active crossovers... definitely lowers noise floor (measurable) but probably because I have ground loops in my unbalanced tri-amp active system. I tried battery power for my DAC and it made no difference that I could hear and I can't begin to measure DAC's issues with equipment I have.
 

signalpath

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Some cheap wallwart SMPS still have some 50/60Hz components in their DC output

Yes. But it's the radiated stuff (transformers, bridges, etc) inside the chassis that's often impossible to shield. Electromagnetic fields are brutal. SMPS makes life so much easier. But another caveat -- do serious listening tests to candidate SMPS in-circuit. Different switching designs can cause variation in perceived audio performance. Some years ago we auditioned over a dozen DC-DC OEM devices for a new high-gain product. They all tested objectively correct (THD, noise, etc.). But only 3 or 4 were deemed usable by blind A/B ear trials. The rest caused identifiable artifacts.
 
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