Plastic Enclosure for a Power Supply.

[Canis guitarus]

I have built a reasonably simple 9v power supply for my pedals inside a plastic enclosure and am now troubleshooting a slight hum problem. Is the lack of sheilding likely to be an issue in a power supply circuit? Thanks for your time.

[brett]

Hi
the hum is more likely to be due to poor voltage regulation or earthing issues than no/poor shielding.
Also check for line loads and radiative sources, such as flickering flouro lights.
cheers

[SpufuZ]

I have biult several of this one:
http://www.generalguitargadgets.com/projects/24-power-supplies/135-regulated-power-supply

I have biuld that circuit in both alu and plastic enclosures and i got no hum in any of them!

May we see your circuit for your power supply?

[Canis guitarus]

I will have to draw it up lol but essentially its 2 of the GG ones built on perf board with a single transformer and bridge rectifier supplying the DC to the voltage regulators.

[Earthscum]

I have a PS that I built (R.G.'s design, if I remember right) that has some big filtering on it, and I use an AC wall wart. I get massive noise from it from your typical ground loops. I have the plastic box with a metal top. When I get hum, I can touch the box and my bass and it goes away. If I plug it into a different outlet than the amp, it doesn't have as much noise. :shrug:

[Canis guitarus]

Ok here is the circuit.

http://www.flickr.com/photos/canis_guitarus/4889968979/

Everything look ok?

[SpufuZ]

That one is stolen from the GGG-site.
You can see the General Guitar Gadgets-waterstamp in the background.

So yes, that one will work very well.

[Canis guitarus]

Absolutely lifted from their site (and many thanks to them) just with the added paralelled VR and smoothing cap.

One thing I did do, since both supply circuits were very lightly loaded, was to put the VRs back to back and bolt them to the same heatsink. Would that make a difference?

[Canis guitarus]

Just on a hunch I upped the value of the first filtering cap to 1000mf, plugged it in and turned it on - quiet as a wee mouse YAY!
Out of interest I separated the two VRs from the common heatsink as well - not a jot of difference.

[SpufuZ]

Ok sorry i didnt realize that i was you who made that schematic!  

Nice to hear that it works allright!

Max A on the TO220 VR´s are about 1-1.5 amps right?
I dont´t think sharing one heat sink with two VR´s will be any problem if you don´t load them with more than about 500mA each. (just my guess and not what i know)
And you can have a LOT of pedals on 500mA.

[Canis guitarus]

No worries lol.
My thinking exactly. The transformer I salvaged was good for 2 amps at 9V and big current VRs are quite expensive so it made sense just to split off the supply to 2 smaller VR's and them balance up the load on the 2 circuits. Its still overkill for what I am running but hey nothing gets hot and you can't sneeze at a free transformer eh?