How to build Linear PSU?

[jean-paul]

In fact I did and the Kitamura Kiden R-cores I had at hand were better than the Amplimo toroids I compared them with. Same VA ratings etc. Some brandless cheap Chinese R-core transformers measured slightly worse. Calculating and manufacturing of excellent transformers is an art slowly disappearing in the Western world so the choice limits itself to Far East products which are not all designed as they should be.

EI/split bobbin etc perform worse than either toroid or R-core with regards to stray fields so let's not include these.

Originally Posted by chris719

R-Core are very good and may be the best choice for some boxes, but there are certainly applications where I'd rather use a toroid or even SMPS.

Yes, just like I wrote. They are the better or best choice in linear PSU's for lowish VA ratings (the subject of this thread).

To tackle an issue one could simplify matters by making the issue either larger or smaller to see its significance (or not). In the case of the standard cheap SMPS that is delivered with DACs etc till let's say 25VA a well designed linear PSU has many positive properties except the price (either ready built or DIY). In fact there are not much things against using linear PSU's. So the logical choice is to replace generic polluting, whizzing, short living RF emitting cheap SMPS for clean well designed low drop low noise linear PSU's and accept the higher price if one likes quality and better results for that added price.

Of course there are the not so cheap well designed SMPS that perform just fine (or even better than many linear PSU's) and exhibit no bad side effects. Well, let those be. Simple.

Last category are the SMPS that are both expensive and tailored for audio. These should live quite some years. Their price is almost similar to linear PSU's though so are they really competing? The ones I wanted to try also seem to fail earlier than they should...

[chris719]

My point is that shielding low frequency magnetic fields is not easy. It is easier to design around the various issues of other transformers and supplies, though.

It is not a question of price or quality. If I was asked to design the best possible DAC it will not have an R-Core transformer 6 inches away from the IO and converter. There is a reason that Benchmark and others are using SMPS, and it's not to save $20. Almost every DIY DAC and preamp design I see here sticks the transformer very close to everything else if it's not a two box design.

The R-Core is almost as good as a toroid in this regard, so I am sure it can be done well, but let's not act like seeing a toroid in a DAC or preamp means it was just a cost cutting measure.

[jean-paul]

That might be (doing stuff right never is easy) but the dishonest comparison in discussions is that one takes the exception to the rule to prove a point which is fine with me. If one buys Benchmark stuff one really does not care what PSU it uses

Linn comes to mind. Their SMPS were told to be excellent and better than linear. I find these often failing in practice though. I am sure many manufacturers buy these SMPS because they are cheaper, lower in weight and they leave the certification and EU stuff to the OEM producer. It is no coincidence that transformers are often the most expensive part in devices despite all fairy tales we are told about SMPS being better. A thinking engineer knows this but it is common to go with the flow and accept a marketing truth for peace of mind.

* Nobody will argue against placing transformers far away from electronics. In fact we were educated to do that. Non discussion. Why would one not follow simple design rules that have proven themselves for ages? To solve self created issues?

[chris719]

I'm not that familiar with Linn, but what would you expect from a company that sells equipment priced like cars .

I'm not sure what you think is dishonest. If I am designing a low power device with a linear supply I am probably going to use a toroidal transformer because it's the best option or very nearly 2nd best and comes in PC mount options, not because it's cheaper. I will have appropriate filtering and regulation. I want, ideally, zero stray magnetic field so I can have more freedom in positioning the transformer.

[jean-paul]

Originally Posted by chris719

R-Core are very good and may be the best choice for some boxes, but there are certainly applications where I'd rather use a toroid or even SMPS.

In our 230V mains voltage world and real life conditions toroids often hum and this depending of the time of the day too. I use these as well and there are differences in quality so one should choose carefully. With R-core I experience no mechanical hum which is a big bonus. Toroids are also too wideband and don't filter as much as R-cores. With toroids the use of mains filtering is a must. So for me toroids should be selected more carefully and they can do a good duty but they are not the best certainly in the lowish VA ratings.

[chris719]

Yes, and you said they were the worst, even worse than EI. That's just not true unless the only parameter you value is interwinding capacitance.

[jean-paul]

Originally Posted by jean-paul

Best transformers are R-Core types followed by EI types and last toroids. The latter are cheapest and certainly not the best. Choose the transformer to be 2x the required load ratings.

Read again, there is a difference between "worse" and "not the best choice"/"not the best" in the languages I speak. Or is this a word game? How many times do I have to repeat that they are not the most optimal choice in many audio devices (based on a set of parameters)?

I am not a native speaker so bear this in mind. It is exactly as you said:

Originally Posted by chris719

R-Core are very good and may be the best choice for some boxes, but there are certainly applications where I'd rather use a toroid or even SMPS.

[wirewiggler]

I wish r- core transformers we’re commonly available and reasonably priced here in the US. Antec transformers (toroidal) are reasonably priced and they ship promptly so that is what I have been using. I wrap a little MU metal around them, not sure how much it helps but can’t hurt. Combine them with one of Salas creations and bang for buck is pretty decent. You could design something yourself but you are basically reinventing the wheel. Add to that Tea bags sells pc boards and complete kits in group buys makes it hard to justify spending to much time on them. I was looking at some of the offerings on EBay - you can buy something in a case for about half as much as you can build it. If I were not so adamant about not supporting a country that trashed the environment and treats their people like slaves I might be tempted, but I like to sleep at night.

Bill
pS Jean-Paul is a pretty smart guy never seen him give bad advice.