DIY Pedalboard power supply

[Les Turnbull]

Picked up a XBox 360 power brick for next to nothing from a car boot sale recently . 12v -  12.1 amp 350wat . Can these be turned down to 9v   and also would they be quiet enough from interference  to use as a pedalboard power supply .

[JerS]

I don't see why not. You will need a large 9V regulator like http://ca.mouser.com/ProductDetail/STMicroelectronics/L78S09CV/?qs=sGAEpiMZZMtUqDgmOWBjgLAmId5B%2fjmHqUoRcImg0wc%3d (TO220 package heatsinked) - Should be quiet enough. This regulator is good up to 2 amps - plenty of juice.

[Les Turnbull]

Yes a pair of 7809 would give 4 amps and should be simple enough to build into a multy out box .

[antonis]

Yes a pair of 7809 would give 4 amps ..

Only with balance resistors, for equal current sharing..

[Les Turnbull]

Im a Noob at electronics so would the resistors go before the 12v input of the 7809 and what resistors would you recommend  .

[duck_arse]

les - I think antonis' balancing resistors go one end to each regulator output and the other ends joined to form the 4Amp output. but do you really need all 4 Amps in one place? you can run the two, three, four regulators to individual daisy chains, as long as their total draw doesn't exceed your reg specs.

you have your regulator spec sheets, don't you?

and welcome to the forum.

[Les Turnbull]

Are you saying that the regulators wont need ballancing and it will be fine to run a daisy chain from each of the 2 regulators .

[antonis]

Duckie says that 4 Amps are quite a lot of current for conventional pedal, even if more than 10 of them are daisy chained to the same PS..

He also says that, if the total current for each individual daisy chain is lower than individual regulator's max rating you can safely feed them without any ballancing need..

He additionaly says that, there isn't need for current sharing (in parallel) of two or more regulators except in case of a sole pedal current demand.. 


P.S.
Duckie, I'll start to charge you for Australian to English translations hereafter...

[duck_arse]

well I thought I knew what I was saying, but I'm not so sure anymore.

a regulator attached to a string of pedals will not need balancing. two regulators joined at their outputs will need the outputs balancing.

[balkanizeyou]

you can also use one regulator with power transistors to increase the current capacity. Question is - do you need that much current in the first place? how many pedals do you use and how many of them are digital?

[Les Turnbull]

I have 7 or 8 pedals 2 of them are Marshall digital  , One regulator  would probably run them all ok and the second reg was a backup/spare . Im not looking to link them together for 18v if that is what Ducky thought .

[duck_arse]

geeze, poor ducky doens't know what to think any more.

antonis - if I was going to balance two regs w/ resistors, what value resistors would they be? I thought I would have thought maybe 0R47 or something, but I don't really think I know.

and then I searched for a pic to illustrate paralleling, diode drop compensation, and power transistor (shunt?) regulator, and they was all in the same page.

http://www.reuk.co.uk/wordpress/electric-circuit/high-current-voltage-regulation/

[Les Turnbull]

I should have explained that what i no about electronics can be wrote on the back of a postage stamp . Ducky,s last post has shown me that it gets complicated with more than 1 regulator so to keep it simple ill try a single 2amp reg .
  Great site by the way . I knocked up a UBE screamer on Breadboard last week and it sounded great but none of the controlls worked but it was fun for a first build so  Ive ordered some more components for a Red Llama and will also give the UBE screamer another try .

[bluebunny]

It's not complicated at all.  You can simply hook up a bunch of regulators to the same 12V input (and they don't have to be 2A monsters, nor even the same part).  Jack has an example at AMZ:



(This is the page the schematic comes from.)

[Les Turnbull]

Thanks for that scema Mark . I ordered a couple of L7809CV but just looked at the spec sheet and its input min voltage is 15v , Will  they not work with my 12v input .

[bluebunny]

I'd be surprised that a 7809 insists on at least 15V input (where exactly did you see this?).  Dropping 6V is excessive - that's 40%.  These regulators usually need a couple of volts to do their stuff, so your 12V input should be just fine.

[Les Turnbull]

It was Farnell,s data sheet. http://uk.farnell.com/stmicroelectronics/l7809cv/ic-v-reg-9-0v-7809-to-220-3/dp/1087089?CMP=KNC-GUK-GEN-KWL-STMICROELECTRONICS&mckv=dxhgk8yQ_dc|pcrid|101042813229|&gclid=CjwKEAiAm8nCBRD7xLj-2aWFyz8SJAAQNalaVYWUcIUzd_Pu_er_40BwtLpfKC2WELvs4RFIjo7A2xoCh-Tw_wcB

[Ice-9]

Have a look for a LDO (low drop out) 9v regulator.

[bluebunny]

The Farnell page may be fibbing.  Many of their regulators show 0V as a minimum voltage!  However, if you look at the datasheet itself (on page 10 for the 7809), it shows the expected range of V_O for V_I from 10.6V to 22V.  Many of the other characteristics also show data for V_I with values well below 15V.  I would say you're good to go with those parts.

[Ice-9]

I use the same ST 7809 regs n my pedals which run off 12v so as Bluebunny says you should be good to go.