power supply....

[Papa_lazerous]

Ok simple stuff I hope.

I have a few wallwarts that I use to power my pedals,  I also own a few positive ground pedals.  That at the moment for ease I use batteries.  I know that I cant connect a positive fround pedal to the same power supply, as firstly you could apply reverse polarity to the pedal and even if it was the correct way round I am going to get a hum big time.  Or so I understand.

So this is what I want to know.

Could I use one standard wallwart for pedals to power my standard neg ground pedals,
and another standard wallwart to power my positive ground pedals observing correct polarity of course

I am thinking being seperate power supplies I wont get issues with gorund loops and humming.

And if I was to build a power supply, I know the regulator used would be a 7809  (78 being positive and 09 being voltage out)  so if I wanted a positive ground power supply would I need to use a 7909 (with 79 meaning negative)  or does it not matter if its regulated on pos or neg?

I have more than likely over complicated this plenty 

John

[jlullo]

i know i'm not adding anything here, but i would like to know the same exact thing!  thanks for asking!

[petemoore]

  k...I'll try a take on it.
  DC is contained/blocked in each circuit by I/O caps, so for DC purposes, a connected WW is 'closed' if connected to that circuit, because on of it's sides ends at DC Blockers, the other to the circuit's ground.
  I'ts effects of the Pos/Neg ground varieties coupled to a power supply that shorting will occur, you connect + To ground, the connect _ to ground = short circuit, every time.
  As far as noise and ground loops, I'd have to wait for someone to educatedly speculate, or tell why/how, or try it out for myself and just see.
  But suspect like all things subjective are subjective.
transformers don't convey ground, one coil transfers electrons to another coil, no direct ground connection...whether the two transformers 'get along quietly' in terms of noise .. I dunno.
  I would guess if there is ripple in both power supplies, 'peaked' ripple waves might occur when they're in phase...and both PS's are in the chain.
  I run batteries on PNP...perhaps the suggest of one 'nicer' wall wart, then use a MAX1044 voltage converter to get 9V_/9V+ going..I've used a few of these to get -9 for PNP FF, 18+V for GR, ez to wire, work great...see data sheet, that chip uses a little voltage, but did everything I wanted for them to do, I put 'em right in the box with the PNP Pos Gnd. circuit I wanted on that' supply.
 

[smallbearelec]

Could I use one standard wallwart for pedals to power my standard neg ground pedals,
and another standard wallwart to power my positive ground pedals observing correct polarity of course
John

Yes, to the extent that you will be providing the right polarities. But the output of most unmodified wallwarts is so poorly filtered that you are likely to be unhappy. Other people can point you to circuits that add regualtion and decent filtering to a purchased wall wart. I find this solution inelegant, but it is workable and cheap. OR, see next comment.

If I wanted a positive ground power supply would I need to use a 7909.
John

Not necessarily. If you build with a standard negative-ground regulator and are very careful to isolate the output from the case, you can just reverse the output leads to power a positive ground pedal. See my Small Wart designs in Projects at smallbearelec.com.

Regards
SD

[jlullo]

steve,
so in essence you could build one power supply that could power both negative and positive ground pedals as long as you isolate the two?

[smallbearelec]

so in essence you could build one power supply that could power both negative and positive ground pedals as long as you isolate the two?

Sorry if I wasn't clear: No, you do need two separate supplies. But you don't necessarily need a negative regulator in either one. I have a Small Wart 200 that powers a bunch of regular pedals, and a Small Wart 60 for the germanium positive-ground boxes. They both use the LM317 (negative-ground), but the output wiring of the Smallwart 60 is reversed: The "ground" of that supply is the "hot" lead to the FF, RM, etc., and the "positive" lead is ground.

[Papa_lazerous]

Thanks Smalllbear   (sorry dont know your real name)

Your last reply made total sense to me. I will build a power supply for positive ground I think.  I got a power brick I am going to use for neg ground circuits.

I am thinking somethign that will put out about 500mA would be perfect for me.  I had to google what a LM317 was.  I was thinking of a 7809 regulator in my head.

I will have to take a look at the power supplies on your site, you got anthing on there that you think will be of use?  I cant say I noticed anything on there last time I was over there.  But then I normally go on there spend my money and leave 

[smallbearelec]

I am thinking somethign that will put out about 500mA would be perfect for me.

To power a couple of positive ground pedals, you don't need nearly that much! 100 ma. is way more than enough.

I had to google what a LM317 was.  I was thinking of a 7809 regulator in my head.

7809 is fine for a fixed 9-volt regulator. Some people like to experiment with over- or under-voltage supplies to germanium pedals, so I did my Small Warts using the LM317, which is adjustable.

I will have to take a look at the power supplies on your site, you got anthing on there that you think will be of use? 

http://www.smallbearelec.com/Projects/ProjandProd.html

I designed the Small Wart 60 specifically for the positive-ground/germanium pedal job. I see that you are in the UK, so that nice, small, cheap Mouser transformer is a no-go for you: It can't be wired for 220. But the  construction ideas can be applied to other roll-your-owns; just be very careful to insulate, isolate and nail down wherever appropriate.

Regards
Steve Daniels

[Papa_lazerous]

I had a look at your project over on your site. I got to say its a really good article. U have got a valid point about 100ma being enough. But maybe i have some tendencies towards things with lots of power or something. The variable regulator is a nice touch indeed, i'm not worried too much about the transformer issue I'll have a look over at Farnell in one they have a good range. Sure something adequate will be available. One thing tho the enclosure u r using. Looks like a hammond. But it has ribs inside which is perfect for slotting the pcb to. But i have never seen one like that. I'm wondering if they are available in the uk