Power Supply design for multiple modules

[JammyBStard]

Some advice would be apriciated.
I'm placing multiple modules, relay boards, relay volume controls and preamp pcbs in a chasis. They require multiple different voltages.
24VDC
12VAC
12VDC

Can I take a 12-0-12 transformer and tap off as shown in the attached? (Caps etc not shown)
I'm wondering if the common ground will cause an issue?

🙏

 

[gdnichols31]

I believe the common ground would be fine.


Looks like a good concept.

 

[JMFahey]

No, it´s wrong.
On negative phase top winding gets shorted.

Besides, no end of 12VAC can be grounded.

To make all this clearer, DO draw filter capacitors and the 12VAC load.
Is it a tube filament?

 

[gdnichols31]

No, it´s wrong.
On negative phase top winding gets shorted.

Besides, no end of 12VAC can be grounded.

To make all this clearer, DO draw filter capacitors and the 12VAC load.
Is it a tube filament?

Agreed, the 12VAC can't be grounded.


How does it get shorted?


Gary

 

[bansuri]

To be flexible with the grounding you need another 24V transformer

 

[JammyBStard]

So the idea, It's going to be a collection of modules running off a common supply.
1. Relay driven preamp input selector (No power on the signal path) 12VAC (rectifier on PCB)
2. Relay driven Stepped volume control (No power on the signal path) 12VDC
2. Single ended jfet RIAA pre 24VDC
3. Single ended jdet Buffer Preamp 12VAC (rectifier on PCB)

So I need 12VAC, 12VDC and 24VDC available
All PCBs will have a common ground through the signal path.

I've attached a more detailed drawing of my idea for the PSU.
I shouldn't be grounding any AC.

Thanks so far!

 

[johan]

You need separate 12V and 24V transformers. As JMFahey said above, the two bridge rectifiers will short out top winding on negative phase.

 

[JammyBStard]

Okay, Thanks all!

 

[gdnichols31]

They are correct, it does short out the top winding. It shorts on the AC side. I was looking at the DC side.


Sorry for the bad advice.


Gary

 

[JammyBStard]

That's fine. The reason I asked in the first place was I assumed if it was possible I'd have seen it done before. Thought there must be a reason why not: )

 

[boogieWoogie]

Suppose JammyBStard did NOT need the 12Vac & 24Vac outputs. Then could he run his 2 DC rectifiers in parallel as shown?

 

[bansuri]

Why do you not derive the +12V from the 24V rectifier with a 120 ohm in series to lower dissipation eventually with a 33V zener to avoid overvoltage