Sorry if it is posted in the wrong thread, also sorry if my English is bad.
I have purchased this amplifier board from aliexpress: Amplifier PCB Link

I have purchased it knowigly, that i have dual secondary tranformer with no CT.
I have found a thread here (thanks to- @ericgibbs ) on how tomake dual rectifier circuit in order to have +v 0 -v (i cannot bridge the 2 secondarys, because voltage goes way wayy out of spec for the pcb itself. )

My problem is: when i connect a 3.5mm to a laptop it works fine and sounds good, but when i connect it to a Desktop PC the signal wire (R GND L) starts smoking and then combusts.

I suspect it may be a Grounding problem, since i dont have any.

Can anyone help me out on how to properly ground this amplifier in a Dual Rectifier setup?

Sorry, i am only getting into electronics and power supplys and etc.

 

You have a ground loop problem. That is, your two power supplies use a different "ground" and thus allow damaging current to flow from one to the other. You should NEVER connect two wall-powered supplies without first checking for this situation. I use a 1KΩ resistor to connect the grounds, look for any voltage across it (or heat) and then proceed with caution.

Your laptop survived because it has an isolated power supply - the battery. If you had your charger attached, you might see the same problem appear.

 

You have a ground loop problem. That is, your two power supplies use a different "ground" and thus allow damaging current to flow from one to the other. You should NEVER connect two wall-powered supplies without first checking for this situation. I use a 1KΩ resistor to connect the grounds, look for any voltage across it (or heat) and then proceed with caution.

Your laptop survived because it has an isolated power supply - the battery. If you had your charger attached, you might see the same problem appear.

Can you please visualise for me what i have to do, because already i had few short circuits. Sorry i am really new to this.

 

Try using an audio isolation transformer connected to the input of the amp.
Triad model # TY-250P

https://www.mouser.com/datasheet/2/410/TY_250P-1892894.pdf

 

How is the audio amp grounded? You show an isolated supply. If that is the full schematic, there should not be a problem.

Bob

 

Your rectifier circuit will work but you can do the same thing with 1 bridge rectifier.
Just connect your secondary windings in series. That effectively gives you a center-tapped single winding at X2 voltage.
The centre-tap to 0VDC. Single bridge rectifier for the +ve and -ve DC outputs.
I would definitely recommend an audio input transformer when outputting audio from a laptop or a mobile phone headphone socket. Saves a lot of grief in case of a fault! Also no ground-loop hum and noise problems.
Good quality 600Ω 1:1 transformers can be fairly expensive but look at an old modem card or fax machine for second-hand parts.

 

I will look into finding an isolation transformer tomorrow and let you know how it went.

 

The one I listed has the best frequency response for the price. 6.00 US.

 

I have tested with known working isolation transformer, tested it on a working amplifier with no ground loop problems, works fine. When I attach it to the amplifier i built myself there is a extremely loud humming noise. (I have double checked that the isolator transformer is far away from main power supply) - still the same loud humming noise. When I remove all input wires and leave it on, its silent. Can anyone assist me with explaining how i can properly ground this amplifier?

 

Currently the 0V is attached to mains ground? Am I doing it wrong?

 

Currently the 0V is attached to mains ground? Am I doing it wrong?

Very much yes! The amplifier circuit must be isolated from the main supply.

 

I will be able to test with isolating the amp earliest after New Years, will let you know how it went. Thanks for the info!

 

I have used capacitors on signal wires to block DC and problem has been resolved.