I think RME and some other manufacturers of professional audio interfaces would take exception to that comment.
(now wearing snowshoes on my asymmetrical isolation feet)
Bear in mind, a warning flag just means to look carefully. It’s certainly possible for someone to use an FPGA, and still produce a good result. The Chord Qutest is an example. It’s just harder, and more expensive because of the smaller product run over which to amortize costs. As @Amir_Majidimehr put it in his review of the Qutest:
I wonder how good of a DAC Rob could design using an off-the-shelf DAC chip. Likely would be just as good and cost a lot less…
Manufacturers of professional audio interfaces, on the other hand, have more things on their minds than simple D/A conversion, things that might not be supported by off-the-shelf chips, so use of an FPGA for such devices might be quite a reasonable thing to do.
Well, maybe Rob Watts has his reasons for doing things the way he does. For example he says:
“ The benefits you have using an FPGA are considerable, as you can have thousands of times more processing power than is found inside high end audio silicon chips. Indeed, Mojo has 500 times more processing power than conventional high performance DACs.
Is there a separate analogue output stage in Mojo or is that derived directly from the FPGA?
Absolutely. An FPGA is entirely digital and cannot have analogue outputs. This is done with discrete components (flip flops, resistors, capacitors and separate reference circuitry). Doing the analogue discretely has big benefits. In designing silicon DACs there are enormous problems - the clock has to be distributed, and this increases jitter, the substrate injects noise and distortion into the analogue parts, the reference circuitry can’t have low enough impedance and is noisy, resistors are non-linear, capacitors are non-linear too. None of these problems apply with discrete DACs.
So does this mean anybody can design their own DAC’s using FPGAs? No I am afraid not. Creating the internal modules, getting them right, getting the DAC technology right, has taken me 30 years to do. This is not easy to do.”
HeadFi has plenty other posts of his going into significant detail about his approach. Of course it is quite possible that amirm knows more about Rob Watts’ abilities than Rob Watts does.
(now wearing snowshoes on my asymmetrical isolation feet)
@Jez, I don’t think we’re disagreeing here. Watts built a good DAC, apparently. And I’m sure he “has his reasons for doing things the way he does.” Though, when you look at that interview, there are some interesting bits I’d call “warning flags”. For instance,
Now, unfortunately, nobody else has recognised this problem
Really? In 40 years of intensely competitive D/A design and study, nobody else has grasped this? He stands alone?
all other DACs have very large noise floor modulation
Really? All other DACs? Once again, he stands alone?
Anyway… While he was spending those “30 years” “getting the DAC technology right”, everybody else was doing that, too. And the results of that journey are captured in modern ASIC DAC chips, just as his are captured in his FPGA chips. And all those “enormous problems” he says that “silicon DACs” have to deal with – by the way, FPGA chips are also made of silicon – are in fact dealt with, in conventional chips.
But I am curious – if the FPGA is only the digital processing part of the Chord device, where is the actual D/A conversion done? I had assumed they were using a mixed-signal FPGA, which contains both digital and analog circuitry.
And while I have no reason to doubt that the Mojo has 500 times more processing power than “conventional high-performance DACs”, it seems all that extra power is unnecessary. Because cheap three-chip designs using off-the-shelf (but up-to-date) components deliver essentially perfect D/A function, cf the Topping D10s we were discussing over in another thread.
Are you talking about getting an LPS for your Core or for your RPi? I personally wouldn’t bother with cleaner power to the core, you might want to experiment with it to your Pi to see if one makes a discernable difference.
FWIW I have a LPS powering a Sonore microRendu (doing the same job as your Pi) into a Rega DAC-R and Brio-R, and I’m very happy with the results - which is what matters to me
I find it hard to believe that reducing the noise in a system isn’t beneficial to the sound (even before the DAC), quite how beneficial and whether that’s the best place to improve your particular system is up for debate.
At the risk of upsetting Bill (how are you my friend) I’d agree that trying a better power supply into the RPi is worth a go. Doesn’t need to be linear though, the £50 iFi iPower is a switching supply but works well. It’s also price appropriate to an RPi.
Don’t know on the NUC as I haven’t tried it (yet )
Jason Stoddard of Schiit uses switching power supplies in his popularly priced Modi DAC. A phone charger or computer data port USB provides adequate power. With well designed internal power filtering, it is perfectly fine.
Jason notes two things: First, design of power supplies is non-trivial and size and filtering are matched to the load. The quality of the power supply design and build matters more than the generic type.
Second, the output of your nifty 5 VDC linear power supply will pass directly into the internal switch mode power supplies that make the voltages Modi or Modius need. Jason suggests saving your money for a good beverage or some concert tickets.
NUC does the same. The 19 VDC supply goes straight into internal switching regulators to make the power the NUC/NUCLEUS needs.
Think about your system architecture. Your nice Chord DAC largely determines the signal quality presented to your amplifiers. The Chord is properly designed to cope with mains power and input jitter. Everything upstream will have limited influence on perceived sound quality as long as the upstream kit has acceptable jitter and noise and is not stalling.
This means you don’t have to take special precautions with your upstream Roon Core and Roon Bridges. Decent power supplies like those provided with your NUC or NUCLEUS and those offered by Raspberry Pi foundation are adequate.
I’m an EE although I never worked audio design. I try to follow along. Over 2020, the HiFi became a big pile of Schiit as GAS Ampzilla expired and I got curious about the Parasound P5. Freya+ has taken its place. A Gungnir Multibit for main converter and a Modius for TV converter.
I’m an electronic technician. From what I’ve read there was a concern that the switch mode power supply uses a clock which could possibly have switching noise of the same frequency getting into the output. Modern switch mode power supplies are now using switching frequencies so far above our hearing range it becomes irrelevant. Along with an output filter that they all now have also overcome this concern. The linear supply was always considered best by audiophiles but there is a bit of smoke and mirrors to make that claim. It is true there would be no switching noise to worry about but what is often not considered is the EMF a linear supply produces. Linear supplies require much more current from the AC coming out your wall because linear supplies are inherently wasteful. Not only is that wasted energy dumped into heat but it also creates a magnetic field pulsing at 60 Hz (EMF). Wires/conductors passing through the 60 Hz pulsing field can have currents induced in them. So the supplies output is clean, the DAC is clean, just keep you analog signals either away from the power supply, or have the signal in a shielded cable. For this reason switch mode supplies should be a fine choice compared to linear. Other advantages of switch mode supplies are, less expensive, more energy efficient, smaller footprint. https://benchmarkmedia.com/blogs/application_notes/152143111-audio-myth-switching-power-supplies-are-noisy
Also bear in mind that physics and logic not necessarily apply with ‘high resolving’ systems. Bought by the economically well, unfortunately quite often at an age which comes with a 12kHz hearing limit. See some YouTube evangelists way up in their seventies. Sure there are miracles … certainly not this many.
A shielded cable will not work against that 60 Hz field, since that couples magnetically to all conductors.
You’d need Mumetal or such highly permeable material to shield the magnetic field.
Audio cables with tightly wound wires and some electronic components to filter common mode interferences are the only way, other than keeping the cable far enough away from such fields.
I can only recommend that the Core, Nucleus, NUC, etc. should not connect to the DAC directly. They belong in the cellar & using a LAN galvanic separater
Connect a Roon-Ready “audiophile” Network Bridge, e.g. sOTM sMS-200 Ultra neo (what I use) or Pro-Ject Stream Box S2 Ultra (w/ LAN galvanic separator) to the DAC, preferably using an optimized USB2 connection. You won’t believe your ears!
Connect a LPS, like my sPS-500, and you’ll be amazed even more!!
BTW: I’m not an EE, just a 55 year old that’s been searching for the audio Holy Grail since 5th grade.
As I have done extensive listening tests with both switched and linear PSUs I can positively say without question that linear supplies improve the SQ. Some devices are impacted more than others. The significance of the improvement may be small with some devices. However there is always a positive improvement.
All LPSUs just like switching PSUs are not created equal. There can be significant differences between between them.
Do the research, talk to people who have actually made comparisons. Then make the same comparisons yourself.
I have fooled myself many times by not doing that. It’s easy to be lazy about it. Best thing is to also have someone else mix you up and try to confuse what could possibly be changed because it’s easy to want to make a prediction or guess.