Maybe not such a good idea, if you believe this: https://www.diyaudio.com/forums/power-supplies/311453-tried-chinese-lt3042-board-4.html#post5561404
Same well functioning PCB but now built in a case with a 220V (we have 230V in Europe) transformer. My take is that the transformer is the weakest point here. There is not much wrong with the board itself but it is not short circuit proof. Its problem is that it is a direct competitor for more expensive devices from other manufacturers 
However, when looking more carefully I see that the PE pin is not connected and I see soldered uninsulated connections to the IEC connector which is not allowed in EU. The PE pin should be connected to the metal case. The mains switch is double pole but only one pole is used which is also forbidden in Europe (both L and N should be switched on and off). The wires to the mains switch are soldered. Normally another type mains switch is chosen combined with insulated connectors. Soldering wires to mains switches is something of the past.
This ready made linear PSU looks like a DIY endeavour and should be modified according regulations. It is NOT safe! Imagine the L wire coming loose and touching the case. Now you touch the case....
However, when looking more carefully I see that the PE pin is not connected and I see soldered uninsulated connections to the IEC connector which is not allowed in EU. The PE pin should be connected to the metal case. The mains switch is double pole but only one pole is used which is also forbidden in Europe (both L and N should be switched on and off). The wires to the mains switch are soldered. Normally another type mains switch is chosen combined with insulated connectors. Soldering wires to mains switches is something of the past.
This ready made linear PSU looks like a DIY endeavour and should be modified according regulations. It is NOT safe! Imagine the L wire coming loose and touching the case. Now you touch the case....
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OK, I have tried to guess what the eBay LT3042 supply is using as passive parts.
The main parts I think should be right, but there some others I can guess only. Like the resistor + LED at the output, or the current limiting resistor for 200mA max on ILIM pin.
There are two resistors that seem to be connected to PGFB pin that I can't guess what values they might be, or what they do.
By joining the VIN and PGFB pins and adding an external transistor, you can increase the regulator current and have the heat dissipate on the transistor. It's shown on the datasheet.
Please check and correct what I may have missed.
The main parts I think should be right, but there some others I can guess only. Like the resistor + LED at the output, or the current limiting resistor for 200mA max on ILIM pin.
There are two resistors that seem to be connected to PGFB pin that I can't guess what values they might be, or what they do.
By joining the VIN and PGFB pins and adding an external transistor, you can increase the regulator current and have the heat dissipate on the transistor. It's shown on the datasheet.
Please check and correct what I may have missed.
Attachments
Same well functioning PCB but now built in a case with a 220V (we have 230V in Europe) transformer. My take is that the transformer is the weakest point here. There is not much wrong with the board itself but it is not short circuit proof. Its problem is that it is a direct competitor for more expensive devices from other manufacturers
However, when looking more carefully I see that the PE pin is not connected and I see soldered uninsulated connections to the IEC connector which is not allowed in EU. The PE pin should be connected to the metal case. The mains switch is double pole but only one pole is used which is also forbidden in Europe (both L and N should be switched on and off). The wires to the mains switch are soldered. Normally another type mains switch is chosen combined with insulated connectors. Soldering wires to mains switches is something of the past.
This ready made linear PSU looks like a DIY endeavour and should be modified according regulations. It is NOT safe! Imagine the L wire coming loose and touching the case. Now you touch the case....
Even if the uninsulated connections are a poor quality finishing and certainly unsafe, Brazil does not have an earth wire in 99.99% wall sockets.
Even what should be the earth wire provided by the electricity company is not zero potential, so it can't be used as safe earth. We use just two wires, 110v in southern states and 220v in northern states. At home I have three 110v phases and one common wire, so I can separate the noisy or heavy current wires from video/audio power.
And as the ground of the building I live is sand, I can't even ground my equipment in the earth with a copper stick
In any case, that shown supply has probably a bigger issue with the long DC output cable it uses. Such a long connection is specifically described on the LT3042 datasheet as something that should not be done. So a simpler LM317 correctly implemented regulator could be used, probably with better results.
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Maybe those DIYers should start lobbying their Governments for starting to care about their countries' citizens... Power grid with 110V a.c. and 220V a.c. just begars belief...
Do what you like but the stated drawbacks are true drawbacks in the real world.
It is forbidden by law to sell such devices in Europe. This device has a metal case which can be lethal when PE is not used. Regulations tell to use PE when metal cases are used. Two prong adapters are double insulated which does not require PE as they are made from plastic. It is quite simple to do things right and safe. That is why normal countries have regulations for electrical stuff. It saves lives.
It is forbidden by law to sell such devices in Europe. This device has a metal case which can be lethal when PE is not used. Regulations tell to use PE when metal cases are used. Two prong adapters are double insulated which does not require PE as they are made from plastic. It is quite simple to do things right and safe. That is why normal countries have regulations for electrical stuff. It saves lives.
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If I remember rightly it is only necessary to connect PE to a metal case of class 1 equipment. You can use plastic, wood, metal (or even chocolate [quote from a regulations inspector]) if it meets the regulations for class 2. In other words you can have class 2 with a two pronged mains input and have an unearthed metal case. See EN60065.
I taken a few Chinese PSU's apart. The transformers have all had 8mm creepage and significant evidence of input to output isolation on the PCB. Where they have appeared to have fallen down is with the EMC regulations. It's an expensive test, if done properly. The solution is to not do it and leave out the components. The emissions below 30MHz where I live are horrendous. For long, short and medium wave listening I now have to use a loop aerial for the magnetic ground wave.
Please do not treat us as children or ignorant people, as if we do things as a caprice, because we want it to be so. This is the real world too, you do not have the last word over that.
It's interesting that we have been able to "survive" many things that are forbidden in Europe, and as I said with no accidents. Or do you think things like that would happen and no one would know about them?
We live in as normal countries as yours, just with different regulations. And lives seem to be safe too.
Sorry?! A lack of regulations elsewhere does not make the issues less true. No more no less. I do not care for areas where safety is ignored. I feel it is my duty to inform as it is my daily job to work in the electrical field. I worked in Africa, Asia (China) and PE is used in those areas as well. Ignorance is often a choice. You can criticise me as much as you want but make sure you understand electrical safety and class 1 and class 2 devices. You wrote that you don't hear or read reports of electrical accidents but I can assure you that many accidents happen with electricity certainly when safety is ignored or not understood. To prevent this many safety regulations and standards have been internationally accepted by various organisations on various continents, not "just a few countries".
If the manufacturer did not opt for PE then he should have used an IEC connector without PE pin and a change in the design. Simple. It would make the PSU more expensive though. I am very sure it won't pass the tests like it is now. It can be a lethal device so not the right thing to buy for unexperienced DIYers.
Just reread this thread. Noticed your remark:
Almost all modern ultra low noise LDO data sheets cover the input and output caps extensively.
If the manufacturer did not opt for PE then he should have used an IEC connector without PE pin and a change in the design. Simple. It would make the PSU more expensive though. I am very sure it won't pass the tests like it is now. It can be a lethal device so not the right thing to buy for unexperienced DIYers.
Just reread this thread. Noticed your remark:
Almost all modern ultra low noise LDO data sheets cover the input and output caps extensively.
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There's an old article in the deceased "Audio" magazine, where Walt Jung and Marsh tested and measured several capacitors types, trying to relate dielectric type to distortion. I don't remember if they also mentioned audio quality with each different cap, but there were many articles and subjective tests from then on that seemed to find a relation between lower DA and better audio quality.
The best on that test were polystyrene and polypropylene types. The worst were ceramics and tantalum.
That's where I wanted to get at. All regulators datasheets I read recommended tantalum solid types to be used with them. Many still do, even if most recent ones go for some type of ceramic types that are less harmful.
Even if I haven't read much on the LT3042 concerning that, probably because it's not as popular yet as the 3X7 chips were.
Many findings you could get on several tests, like not using low ESR capacitors on the 3X7 regulators, were never mentioned on datasheets. Maybe because people who make datasheets do not care for subjective results? Even if they contradicted what they recommended?
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@carlmart,
What Jung and Marsh were referring to were capacitors in the audio signal path, not power supply capacitors. There are very good reasons that certain types of caps are specified for use with voltage regulators, such as to prevent a regulator from turning into an oscillator. Same type of thing for caps used to decouple IC power pins. Caps that can affect audio quality are those used for things like signal coupling, audio signal filtering, dac I/V converter feedback caps, etc.
In addition, some ceramic caps are great for audio sound quality and some are terrible when used in the signal path. C0G and NPO types are very high fidelity and as good as any cap out there for audio signal use. Ceramics such as X7R and Z5U are for power supply decoupling, not for the audio signal path.
EDIT: The above is kind of the short explanation. It can get more complicated in some cases when there are multiple factors acting at once. Unfortunately, there is no simple rule that polystyrene is always better for any and all applications, or anything like that.
What Jung and Marsh were referring to were capacitors in the audio signal path, not power supply capacitors. There are very good reasons that certain types of caps are specified for use with voltage regulators, such as to prevent a regulator from turning into an oscillator. Same type of thing for caps used to decouple IC power pins. Caps that can affect audio quality are those used for things like signal coupling, audio signal filtering, dac I/V converter feedback caps, etc.
In addition, some ceramic caps are great for audio sound quality and some are terrible when used in the signal path. C0G and NPO types are very high fidelity and as good as any cap out there for audio signal use. Ceramics such as X7R and Z5U are for power supply decoupling, not for the audio signal path.
EDIT: The above is kind of the short explanation. It can get more complicated in some cases when there are multiple factors acting at once. Unfortunately, there is no simple rule that polystyrene is always better for any and all applications, or anything like that.
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What supply exactly did you buy? It's good to know that.
About looking for such stuff on eBay first, I can't agree more. Avoiding pitfalls if possible.