Hi folks
I'm in the early stages of building my own DAC.
What I'm wondering is this - would it be worthwhile to split the PSUs into a separate box from the other circuitry for better isolation, shielded etc.
Furthermore would there be any point in splitting the digital and analogue stages into separate boxes as well?
I'm in the early stages of building my own DAC.
What I'm wondering is this - would it be worthwhile to split the PSUs into a separate box from the other circuitry for better isolation, shielded etc.
Furthermore would there be any point in splitting the digital and analogue stages into separate boxes as well?
Usually, it isn't necessary or desirable. With small components working at high frequencies usually better to keep interconnections short as possible. In cases where there may be strong-ish EM fields or higher currents, usually good layout practices can manage any potential stray coupling concerns satisfactorily.
Makes sense if you're using EI transformers in the power supply to have them in a separate box. Otherwise magnetic field leakage may well induce hum into your circuits.
EI transformers have better isolation from mains (lower inter-winding capacitance) than toroids.
Separating analog and digital into separate boxes - can't see the point of that, though if you have a lot of digital processing you may do well to keep that in a shielded 'box' (with a screening lid on it) on the PCB.
EI transformers have better isolation from mains (lower inter-winding capacitance) than toroids.
Separating analog and digital into separate boxes - can't see the point of that, though if you have a lot of digital processing you may do well to keep that in a shielded 'box' (with a screening lid on it) on the PCB.
In general, when you want to minimize magnetic coupling between two wire loops, you can increase the distance between them, reduce their areas or orient them at 90 degree angles. At high frequencies you can put a conducting plate in between them as a shield. To minimize electric coupling between conductors you can reduce their areas, increase distance or put a shield in between them.
As you want to convert a digital signal into an analogue one, there must be a mixed-signal part somewhere where digital and analogue come together. That means that you can't keep all digital current loops at large distance from all analogue loops.
When you put all digital processing in one box, connect it with a 3-metre-long cable to another box containing the mixed-signal part and connect that with another 3-metre-long cable to a box containing the analogue stuff, you have to use very well-shielded cables and think very hard about where all return currents will be flowing or the coupling is likely to be made worse by the relatively large wire loop areas.
When you put everything on one PCB with thin shielding plates in between the digital, mixed-signal and analogue parts, placed such that no loops need to be made larger, those plates can only help.
In my DIY DAC designs I used four-layer boards with the digital stuff on the bottom, mixed-signal and analogue on the top and the inner copper layers as shield.
For power supplies it does make sense to put them in a separate box placed at a large distance from the rest. When you use a transformer working at 50 Hz or 60 Hz, it is difficult to shield any stray field it may have (low frequency magnetic fields are hard to shield because of their large skin depth). The cables from the supply to the circuit essentially carry DC and are therefore not likely to cause interference.
Whether it is really necessary to place the supply at some distance is another matter. In my experience it is difficult to make phono amplifiers with EI mains transformers free from hum unless you place the transformer at a considerable distance, but I haven't had any hum problems with my DAC with toroidal transformers.
As you want to convert a digital signal into an analogue one, there must be a mixed-signal part somewhere where digital and analogue come together. That means that you can't keep all digital current loops at large distance from all analogue loops.
When you put all digital processing in one box, connect it with a 3-metre-long cable to another box containing the mixed-signal part and connect that with another 3-metre-long cable to a box containing the analogue stuff, you have to use very well-shielded cables and think very hard about where all return currents will be flowing or the coupling is likely to be made worse by the relatively large wire loop areas.
When you put everything on one PCB with thin shielding plates in between the digital, mixed-signal and analogue parts, placed such that no loops need to be made larger, those plates can only help.
In my DIY DAC designs I used four-layer boards with the digital stuff on the bottom, mixed-signal and analogue on the top and the inner copper layers as shield.
For power supplies it does make sense to put them in a separate box placed at a large distance from the rest. When you use a transformer working at 50 Hz or 60 Hz, it is difficult to shield any stray field it may have (low frequency magnetic fields are hard to shield because of their large skin depth). The cables from the supply to the circuit essentially carry DC and are therefore not likely to cause interference.
Whether it is really necessary to place the supply at some distance is another matter. In my experience it is difficult to make phono amplifiers with EI mains transformers free from hum unless you place the transformer at a considerable distance, but I haven't had any hum problems with my DAC with toroidal transformers.
Thanks guys, this is precisely the sort of feedback i need.
So, no point in putting analogue and digital stages in separate boxes.
Some possible benefit from putting PSUs in separate box.
I think I might run into some space issues trying to get everything into one box, another reason to have the PSUs separate.
Hmm, things to think about...
Any other pros-cons to a separate PSU box I should consider?
So, no point in putting analogue and digital stages in separate boxes.
Some possible benefit from putting PSUs in separate box.
I think I might run into some space issues trying to get everything into one box, another reason to have the PSUs separate.
Hmm, things to think about...
Any other pros-cons to a separate PSU box I should consider?
My friend, a Buffalo DAC aficionado, is the one who built it. He also chipped in the IVY and some other parts. Using 4-pin mini DIN plugs for the power cord was a really nice touch, but they are turned out to be a real pain for him to solder and assemble. Full size DIN plugs may be a better choice. In any case, it's great to have the cable be detachable, unlike the umbilical between my AI preamp's power supply and main chassis.
It's time to block some of the holes in the power supply case, and I may move the dac / line stage to a nicer case at some point. But the results have been great. I've always been a vinyl listener, but this DAC really changed my opinion of digital front ends.
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