9/18 V power supply, no common ground

[congo77]

Hi.

I have plans for making a 9/18 V power supply with 8 9V jacks and 4 18V jacks for my pedals. I will put it in a metal box with output jacks and so so, that’s no problem. My problem is what circuits to use and how to do the wiring. I want it to work like the “Voodoo Lab Pedal Power 2” with isolated outputs. I quote

“Isolated outputs.
Each output is completely isolated. This means that you won't have any ground loops or interaction between pedals that can cause hum and noise. It also means that unlike other "common ground" power supplies, you can run effects that have both negative and positive grounds without difficulty.”

My first plan was to use 7809 and 7818 regulators for each output jack and feed them with two external 12V 2A and 24V 2A switched power supplies but then I have a common ground. The elimination of common ground would be really great if I could achieve that, ground loops can cause a lot of problems.

Anyone who has any good ideas?

[UnklMickey]

this is a really tricky problem.

even if you had a single transformer, with separate bridge rectifiers, filters, regulators etc., for each output, when you connect them to the pedals, the positive and negative grounds would cause problems. (shorting out the transformer)

so the only way i can see to do this, would be to have separate transformers (or at least individual secondaries) for each and every supply.



unk

[ChrisK]

If a switch-mode topology is used (most likely a buck [step-down]configuration), additional windings, diodes, filter caps, and post-regulators (if needed) can easily be added to the output coil (it becomes a transformer) for each. A primary output load is necessary to ensure regulation, and it should represent at least 50% of the total output load.

Also, a push-pull DC/DC converter can be used with several small toroidal output transformers. Being a self-oscillating design, one can generally just add transformers up to the drive limit of the switch transistors. I often see such transformers available surplus. Assuming a center-tapped output winding, one can either full-wave center-tap rectify the output for 9 volts, or full-wave bridge rectify for 18 volts.

Another approach that can be used is that isolated 9 volt output switching modules are readily available surplus from the old coax-based Ethernet days. Build a primary supply for the modules (as needed) and just keep adding modules. If the switching module requires an output capacitor for filtering, it may not have one internally, and a voltage doubler could be used for 18 volts. If not, stack two.

[good_samaritane]

Hi, GN2:

Have you solved your problem?, if not you can try this:

www.generalguitargadgets.com/index.php?option=content&task=view&id=78&Itemid=107

[congo77]

Hi.

Thanks for your thoughts guys. First, here is an article with a guy who has a solution to the problem www.geofex.com/Article_Folders/Spyder/spyder.htm . Second, I have found my own solution. The power supply was intended to be used with a pedal board. I can buy unstabilzed 12 V 300 mA power supplies at 4.00 Euro a piece. I use these PS as they are, put connectors on the pedal board and then I put the voltage regulation and the filtering inside the pedal board. It gets economic, no 230 V hum fields near the guitar signal cables, reasonably easy to handle and flexible (6x9 V, 2x18 V and 2 straight cables for special power supplies).

Thanks