Toroidal transformer, where is the GND?

[MilanAudio]

Thank you very much!

Thank you very much, not it is perry clear and + some bonus information!

You need to know the phases of the secondaries, see this thread How to determine phase of transformer secondaries?

and

I f you start making test with transformers connections always use a usual lightbulb in series with the mains ...
Light Bulb Current Limiter Build Thread | The Gear Page

I noticed this:

View attachment 767192

It's cool, because now I can have 0V even my transormer has only one secondary

 

[edgew]

Question

Hello,
I have read this thread but I am still unsure if i get it.
I have two power supply modules which have AC/GND/AC as input and V+/GND/V- as output. For two amplifiers with TDA7294, to have dual mono amplifier.

I dont have access to center tapped transformer so i wanted to use 2x24V and wire together the secondaries. So i can connect the AC/GND/AC on the power supply

My questions are:
1. Can i use one transformer and connect it to both power supplies? If yes how?
2. When using 2x 24V transformer will i get the right voltage? For my amplifier it should be no more than 40V and as i understand it i will get +33 0 -33 as output. Am I right?

 

[miro1360]

1. yes you can use one transformer for both power supplies, simply parallel the power supply boards (use transformer with power >150VA) ... *find the right center tape point
2. 2x 24Vac * 1.414 = +-34Vdc

* easy way to find the right center tape GND on your transformer (2x 24Vac) with separate windings:

- mark the wires as follows:
-- winding 1: A1, A2
-- winding 2: B1, B2

- connect together wires A2+B1 as "GND" representation and measure the AC voltage between A1 & B2
- if the voltage is 48Vac then you found the right center point as GND

- if the voltage is not 48Vac but is smaller, about 0-2Vac then disconnect the wires representing "GND" (disconnect A2+B1) and connect together A2+B2 as "GND"
- measure the AC voltage between A1 & B1, now it should be 48Vac, and you found it

 

[edgew]

Thanks @miro1360,
just for confirmation, it is safe to connect it as in picture?