Here's a circuit from https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/diode-diode50.gif:

Just ground the node between C1 and C2 and you have the start of a bipolar supply.

 

Super ! Many thanks mister @dl324 !

 

Better still, get a transformer with a center tap on the secondary winding.

 

Super !

A center tapped transformer would be better, but untapped transformers seem more common. I've picked up AC wall warts from Goodwill, but haven't seen a center tapped one in decades. If you're comfortable working with line voltage, go for it.

 

@dl324 and @MrChips
Indeed mrchips circuit I found it abundantly on google. The problem is that i dont have the 79xx regulator. I only have 78xx. And to get it, i must wait 2-6months from ebay. So i needed a quick solution. Thats why im complaining here, otherwise i have been building it already.
About middle tapped transformer, i have this very low power, bazaar type, multiple voltages steps transformer 3-5-7-9-12V(i know its values from memory). I think i can use 3 wires from those outputs... even if they are at different voltages, the difference is not that big. (Those holes, I made them for venting, and they did their job good enough; Im proud of them..some ~20 years ago).

dl324 solution is uncommon in my google findings and I like it, more than what i find, i will try it very soon, mostly from curiosity. I have a single secondary transformer 220-12v AC, not that great in output current but perfect for this application here, and that I most probably use for this solution.
- MY solution is to put in series these 2 power supplies (electronic transformers?). They are from UK, a friend send them to me exactly for this purpose, to use them for tests or definitive projects; on my request, some time ago. So if will burst in flames, I will not cry for them, they were free. I hope they wont get fire. I didn't test them yet, some surprises on the way still. :] I hope they will still work.

Excellent support so far.

 

Hold on. We're not done yet.
When I come back in a couple of hours I will show you how to do it with two resistors.

 

@MrChips I actually think myself for a couple of days on a wire combination of some sort, yes, that basic.
The problem that i come with is that involves 2 transformers... or 2 secondaries. Minimum 2.
So... it is possible only with wires! That is the most basic it can get (or I can get).
But ,as i said, from 1 transformer will be more important and practical. Thats why im raising the flag here.
I am very curious what you will come with, with the resistors....
I might GUESS... you will shoot for a minimum current for the chip, like 10mA or so, from 1W (probably) resistors made as voltage divider? Again im trying to hit your thought there. It might work... im not good at this kind of math, so its no problem, take your time, im not in no hurry. Until then i might try something and update it here.

 

i have this very low power, bazaar type, multiple voltages steps transformer 3-5-7-9-12V(i know its values from memory). I think i can use 3 wires from those outputs...

You can only select one voltage and they're probably not independent, so you couldn't stack them even if you hacked the adapter.

Using wall warts would be the safest. I built a box to hold a bunch of transformers I had laying around so I could use them safely:

 

Which planet do you live on?
Today I can buy a modern opamp or a 79xx negative voltage regulator at the electronic parts store "down the street".

 

If you are just powering an uA741 opamp, then 10mA @ +12V, GND, -12V will do it.

Build a 24VDC power supply and add two 1kΩ resistor across the supply rail.
Take the junction at the resistors as your GND reference point. Put 10μF electrolytic capacitors across each resistor.
There are other ways to do it but try this for now.

 

@dl324 Indeed i didnt open my bazaar transformer, so maybe you are right. It was a first idea using him as a split secondary.
Very neat idea with your transformers box. SO you gather all laying around transformers and put them inside a supply box? Pretty smart idea. I have a small box and a groceries bag half full of wall transformers. Probably around 20 in total. And some are not new or good. Some are damaged and not working. I already tested those 2 electronic transformers i put on the table, and 1 of them is busted, I changed a cap that had an obvious rounded top hat, but still no life in it. It might be some smd resistors too... Ill have to test another one then. Yah, i like your idea with the box full of transformers very much. What are those big blue capacitors there? For filtering? or just part of an unseen board?

 

SO you gather all laying around transformers and put them inside a supply box? Pretty smart idea.

I just put a handful in a box with voltages I was likely to work with so I wouldn't have to deal with connecting them to line voltage. Back when I was young and foolish, I used a "suicide cord"; basically a power cord with the non-plug wires terminated in alligator clips. After swapping line and neutral once and connecting my scope ground to the hot wire, I pretty much stopped using them.

What are those big blue capacitors there? For filtering?

You got it; filtering.

There's a bridge rectifier wired to the 5 binding posts in the upper right corner. The switch connects the capacitors in series or parallel so I could easily make a split supply.

 

If you have a bag full of AC to DC adapters, find two that are identical.

Wire the two in series, -ve terminal of #1 PSU to +ve terminal of #2 PSU.

 

mister @dl324 , make me a circuit of your power supply. On paper is fine, no need of fancy simulators.
Some obvious things are escaping me only from the 2 pictures. I presume you wired in paralel all the transformers to the mains, and for each secondary you put filtering capacitors (but why so Big, and 2 of them, and a comutator on the front panel for them? a bit weird) that should be interesting to see why is for. Im not presuming much because you also have (again, probably) in paralel also the rectified secondaries as well.... from reading the front panel. And some leds as well.
Best is to make the circuit for me. Your time to shine has come. I like to shine as well so you are welcomed. :] If you like of course.
And thanks.
I have a single transformer 220V-12VAC. It will output +6 and -6. I think it will be enough. And yes its only to power the opamp. Well, also +6V to 0V to power the rest of very minimal current around the opamp, like some resistors and probably caps or transistors, in the future, but until those, resistors mostly.
@MrChips yes, half of bag, and I already selected 2 of them that are working already. Is in plan both negative power supplies to make. Thank you !

 

@MrChips I made your circuit
from my 220-12v transformer and i have +6v 0v +6v
But -6v is not present on any terminals.
I put originally, both C minus polarity towards 0V.
Then I changed one C with + at 0V and - to one terminal.
Still, same value +6v 0v +6v
Ive added 2 diodes after each terminal (1 diode per terminal) and i measured after diode on Vcc multimeter, and still, no - sign.
maybe a rectifying bridge after each terminal and 0V ?

 

How are you measuring voltages? Red led to where? Black lead to where?
Show your setup.

 

I tried everything.
I measured between V1 and V2 terminals and it gives me 9V
I measured between gnd and V1 ; gnd and V2. on both i get +6V.
If I inverse the lead probes, i get -6V on both as well.
Best if you tell me how is done.

 

This should be simple, but it is not.
It is also my first time when I go into the realm of shadows , the negative power supply -6V !
So... weird stuff is lurking here. But is exciting. Learning new stuff.
This simulated circuit... is promising.
For half wave, V+=-200mV & V-= -24V then for the oposite half wave V+=24V & V-= 200mV. It is passing through 0v, not stopping at it.
I think this might be it ? Its interesting that i set the alternative source as 12Vac but i get 24 in the output. I hope it will be good enough current.

 

This should be simple, but it is not.

Get rid of the bridge rectifier. Circuit ground is the node between the two capacitors.

With 12VAC, you should get about about +16V and -16V.

 

You see how the blue wire V- is passing over 0V when V+ is at peak?
Interesting ! Probably is because of the capacitors... Who knows.
It would be nice if i had an osciloscope in real life... mmmmmmmmmmmmmmmmmm. :]