Pedalboard Geofex Spyder-ish power supply

[IvarsOzolsDB]

What is the point of using multiple secondary transformer in Geofex Spider PSU? Can't single high amp secondary AC winding be used with array of multiple bridge rectifiers -> capacitor filters -> regulators etc? Same AC potential, not connected DC grounds on PSU outputs...

[Ice-9]

The whole point of the multiple transformers (or multi secondary) IS for isolation for each regulated output, this would not be the case if a single transformer was used with one secondary winding (common ground connection through the secondary for all outputs).

[IvarsOzolsDB]

Check out transformers T1 and T2, this is simplified schematic of Geofex Spyder with two outputs. Transformer T3 is the variation I'm talking about with also two outputs. I think in all the cases GND1 trough GND4 is connected together ONLY trough audio input-output cables of pedals, but not in power supply - thus no ground loop. Am I wrong?

[Ice-9]

As I said this is not isolated outputs as the two rectified and regulated outputs share a common secondary and are connected electrically. (GND3&4)

What you could do is use the small block transformers that have 2 secondary outputs this would give you 2 outputs from 1 transformer (not a centre tap winding).

[Phoenix]

Check out transformers T1 and T2, this is simplified schematic of Geofex Spyder with two outputs. Transformer T3 is the variation I'm talking about with also two outputs. I think in all the cases GND1 trough GND4 is connected together ONLY trough audio input-output cables of pedals, but not in power supply - thus no ground loop. Am I wrong?

Sorry, that does not provide isolation between the two 9V supplies. Imagine this, if they were actually isolated from each other, you could connect them together in any way you wanted, right? Say put them in series for an 18V supply. So if you were to connect GND3 to +9V 4, what do you think would happen? The lower diodes of B3 and the upper diodes of B4 would all be short circuited! The GND3 and GND4 are referenced to each other through the diode bridges. See, diodes do NOT provide isolation - that is why it is completely unsafe to directly rectify the wall voltage without using some GALVANIC isolation - that is a transformer. Sorry, but there's no way around this. Even the miniature switchmode power supplies that directly rectify the wall voltage then chop that up and put it through a small transformer at high frequency (that's why they can keep the transformer small) to provide isolation.

[Ice-9]

The schematic below shows 2 transformers each have 2 secondary windings, this will give you isolated outputs. The other picture shows the type of 'Block' transformers I have used.

[IvarsOzolsDB]

Ok, got it, thanks (feeling foolish now)!  I'm planning to do this PSU in similar manner to schematic You posted.

Other thing, how about safety grounding to chassis in isolated PSU scenario?

[Ice-9]

Ok, got it, thanks (feeling foolish now)!  I'm planning to do this PSU in similar manner to schematic You posted.

Other thing, how about safety grounding to chassis in isolated PSU scenario?

Grounding of the chassis should be from the mains cable earth not directly through the 0v of the 9v Dc outputs. Do some research on operating with mains devices before jumping in and messing around with mains which can kill you.

[IvarsOzolsDB]

Well, normally in mains connected equipment all DC grounds are tied to chassis ground, but this would screw up ground isolation and defeat the purpose...

This is what I came up with, mains fuse holder will be mounted on enclousure, transformer is 2x12V 2x250ma. Did not put another pair on same board for versatility, so one can get any number of outputs needed.