Hi,
"GND" is just a name ... and it shoud be the signal where (most of) your voltages refer to.
You may name every signal "GND" .. it´s up to you.
Example:
If you name the upper node "GND", then the center node will be -5V and the lower node will be -10V.
If you name the lower node "GND", then the center node will be +5V and the upper node will be +10V.
At least the designer should know if this naming makes sense or not.
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In your schematic the problem is that you need about equal currents in the +5V path and in the -5V path to ensure symmetry .... otherwise the voltages may float and the regulators are not able to maintain the specified ouput voltage.
I recommend to
* omit the bridge rectifier
* connect the lower transformer pin with GND
* connect a diode from upper transformer pin (A) to the positive bulk capacitor (K)
* connect a diode from upper transformer pin (K) to the negative bulk capacitor (A)
The drawback is, that the voltage ripple at the bulk capacitors will be about twice as high.
The benefit is you need only two diodes, that generate less voltage drop and less wasted power...
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A 9V AC, 3A transformer will generate about +/-12.7V peak at full load maybe +/-15V peak when unloaded. Consult the datasheet or test this....
Klaus