Power supply

[Laudanum]

Been a while since I posted.  Not related to a Bottlehead build but I figured the crew here could help with a dumb question.   I'm thinking about building a power supply for a pedal board.  Using a multi secondary transformer for several 9Vdc outputs.   The jacks would be standard 2.1 x 5.5 wired for center pin negative.   I'm confused about the regulator.  I'm seeing some info about using negative voltage regulators but I'm thinking I can just use a standard LM7809.  Just hook up the sleeve of the jack to the + side of the circuit and the pin to the - side.   Am I missing something?

Thanks

[mcandmar]

7809 should do fine, provided the pedal runs off 9v which as far as i know most of them do. i.e. a single 9v battery.  I dont think you will need a negative supply, unless a specific pedal does in which case it will either have two 9v battery's inside, or run off an AC supply.

I would build a beefy B+ supply ~12v with plenty of smoothing capacitance, then feed that into multiple 7809's in parallel for each output.  If you look at the datasheet it will give you guidelines for local decoupling capacitor values, usually ~.1uf on the input and output pins, then add an output capacitor as a reservoir on each output.

http://www.diystompboxes.com/ is a great resource for pedal schematics so you should be able to find a few for commercial power supply box's.  It would be worth studying a few to see the capacitance sizing and grounding layouts the real box's use.   I suspect in this day and age most use tiny switching power supply's so you might have to go looking at older units from the 80's and 90's for linear supply's.

Also post pics when your done as i might build one too, building a few pedals has been on my todo list for a while...

P.S. center pin negative is an evil practice, why on earth would any manufacturer do that

[Laudanum]

Thanks for the info.   I have come across a few DIY builds online to see what type of capacitance they are using.   Just have to decide if I really want to build it after running through the costs compared to some of the better available, ready made supplies.   I think I can do it for a fair amount less to be worth it, but have only done the math in my head.   My biggest thing these days is that if I can build it, I can fix it.    

Thanks again.

[mcandmar]

You can buy a good supply for $100, but by the time you source a suitable enclosure, sockets, and transformers you will be most of the way there.   I dont see any significant savings to be had building your own, but the sense of satisfaction may make it worth it

If you are in no hurry you might find a few bargains on eBay, i've found transformers and other parts for projects for pocket change in the past, and things like the DC sockets you can buy from china for next to nothing.

[Doc B.]

I'm posting a link to my neighbor Matt's The Mad Ape online store, as his primary business is selling guitar pedals. Maybe there is some info there to help guide you in your choice.

http://www.themadape.com/guitar-effects/power.html

[Laudanum]

You can buy a good supply for $100, but by the time you source a suitable enclosure, sockets, and transformers you will be most of the way there.   I dont see any significant savings to be had building your own, but the sense of satisfaction may make it worth it

If you are in no hurry you might find a few bargains on eBay, i've found transformers and other parts for projects for pocket change in the past, and things like the DC sockets you can buy from china for next to nothing.

My first choice to purchase a supply would probably be a Voodoo Lab 4 x 4.   At any rate,  doing the math, I can build one for under 80 bucks.  I have some of the passives on hand, as well as an enclosure that should work, hardware and board material (vero and copper clad [I can etch]).  Also have a power entry module.  Only thing I need is the transformer (Weber $25), jacks, regulators, and maybe bridge rectifiers if I don't want to use individual diodes.   Yeah, ebay is much cheaper on jacks than Mouser.  Save another 10 bucks on jacks alone.   

But, the link that Doc provided has some nice deals (Thanks Doc B), so I still have to decide if I want to take the time for saving 20 or 30 bucks and/or having a few more outlets.  It would also be a bigger box.   I'll probably do it anyway.