48Vdc Phantom power supply starting from 12Vac


Hello everyone.
Here is the wiring diagram, the file for the LT Spice simulator and the photos of a power supply suitable for condenser microphones and In the box (Direct Iniection box), all used in the music field.
The guide is quite simple and I avoid going into the topic too much because if you have found this page it means that you already know what it is used for and how it works. If you came here by chance or out of curiosity, you can ask questions, to which I will be happy to answer. Before asking, But, take a ride on the net because there is one literature in this regard very exhaustive.

You won't find the printed circuit board design, those who know me know that I HATE doing them. If there is someone of good will who wants to try well,.

The most interesting part was simulating the full wave voltage multiplier and the subsequent zener diode stabilizer in the four combinations of boundary conditions. These conditions are mains voltage between the minimum and maximum declared by the’ ENEL (230V ±10%) and output load of the power supply disconnected or completely short-circuited. With the indicated values, perfect operation is obtained without damage in all possible combinations and in continuous service (24 hours a day), provided you choose a transformer that is also suitable for continuous service.

NOTE: I added a 100k resistorOh parallel to C5 so as not to leave the capacitors charged once the power has been removed. This change is not shown in the diagram.

Wiring diagram
Components list

Recommendations: keep an eye on the polarity of diodes and electrolytes. E’ true that we are talking about small powers, but the possibility of roast or end of year barrels is just around the corner….
The two 6.8KΩ resistors (R3 and R4) are referred to as 1% of tolerance and IN THEORY it is important that in addition to being as equal as possible, they are metallic in layer. If you do not have them, normal carbon resistors are fine as well after having selected two IDENTICAL ones among them. What changes is the noise generated by the resistances themselves, but if you have equipment that can make you hear the difference in noise between the metal layer and coal ones, you will already have Phantom power available in the aforementioned devices, so the problem is solved at the root. Identical recommendation for R5 and R6.
A curiosity: the 270Ω resistor R2 could be eliminated by making R1 double the value as it is now, but the power had to be doubled as well. So I preferred to use two, it is more beautiful to see and better distributes the very little heat generated.
The last note concerns the two Zener diodes that could be replaced by only one of the standard value of 47V (the allowed tolerance is up to almost the 10%), but then it would have been too much at the limit of the power dissipated in the unfortunate case of ENEL at maximum and no load. I thought that one more Zener diode doesn't do too much economic damage.
The last note…. but I hadn't already written it? Oh well, then the first one was the penultimate one. I said the last note concerns the power of the necessary transformer, which in no case reaches 2VA, so a tiny transformer with the secondary 12V 170mA is already enough, if you have one with the capacity to supply more current it is okay, provided it is 12Vac.
The very last note (so don't scold me!) is that you must first connect the Phantom power supply to the microphone and then turn on the Phantom power supply. The connection to the amplification system can be done before or after, as long as the volume concerning the microphone is set to zero. Don't write to me that you did it and you won't hear anything, it is very normal, I made you turn the volume down to zero…..
To turn off turn the usual volume to zero and AFTER turn off the Phantom power supply. If you want you can at this point disconnect the cables and / or turn off the rest. This sequence serves two things attributable to one: don't break anything. Failure to respect it MIGHT break something in the microphone or in the input stage of the amplification system, in addition to having very high noise peaks that could damage any loudspeakers.
One more note (ok, this is really the last): when using something powered by the Phantom E’ IT IS FORBIDDEN to connect or disconnect the relative cables with the Phantom turned on, as well as E’ IT IS FORBIDDEN to have cables broken or ending with oxidized pins and / or of dubious quality. A false contact in this case generates very high voltages, with relative risk of electrical breakdown of the appliances and mechanical of any speakers.

Some photos of my HORRIBLE realization. The container is recovered, like everything else. It was an old igniter for discharge lamps. Actually the container should be metallic and connected to the circuit ground (leg 1 connectors) to reduce the possibility of the circuit picking up any electrical interference.

With a little mechanical work and a few coats of paint it has become so:

Then I assembled everything in a flying way, TECHNIQUE THAT I DO NOT RECOMMEND. A breadboard is fine, in my case I had not considered the size of the connectors all’ inside the box, there was no space left for a board with electronic components.

And finally the device is finished and connected.


5 replies
  1. Amilcare
    Amilcare says:

    Finally you too have published your first article. I must say that even if minimal, it has its own study and usefulness behind it.
    For me a great article that presents simple solutions to real problems, and as if this were not enough with recycling and reuse of things born for quite another use.
    What more if not EXCELLENT WORK

    • maxmix69
      maxmix69 says:

      Thank you so much Amilcare. How did you get hold of it, despite being a minimal project, the study behind it is all right! Seems like a simple thing, but it is not so immediate to make ends meet. You don't know how many I see (also sold commercially) that don't work well. Not to mention the various heinous schemes I see around, no one who cares about going to read the specs of how it all works. I have been building them for years for friends in many different ways, now I had to draw the schematic in electronic format and assemble one specifically to propose it here. It didn't weigh me, I did it willingly.


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