Which voltage Regulator?

[newfish]

Hi All,

Am currently building a Bobtavia for a friend of a friend.

Up until now, I've only ever built 'Battery' pedals - not using wall-warts for anything other than Digital(Delay / Pitch Shift) boxes myself.

I've had a request to include a 9v power jack on this particular box - and am keen to do so as I've never done it before.

Looking through datasheets etc, I'm drawn to either the LM317, or 78xx series of regulators - to give 9v DC.

Does anyone have any suggestions as to which one to go for...

http://www.maplin.co.uk/Module.aspx?ModuleNo=7939#specifi

http://www.national.com/mpf/LM/LM317.html

...I'm looking for as small a board as possible - with the intention of making 'extra' boards in their own boxes to go between Wall warts and commercial Pedals as an extra assurance of good voltage, sort of like this...

Wall Wart ---> Regulator Box ---> Pedal   

I realise that using a regulated PSU would negate the need for this, but am thinking it would be a useful 'Gizmo' to have in my case - bacuase you never know what the other guys in the band are using...

[km-r]

78xx is the way to go! it does not even need lots of external components.
ive done mods to distortion boxes by soldering the regulator right on the DC jack...

[doitle]

I'd just like to point out that this not an optimal way to run any Vreg. Their performance is largely based on the differential between the input and the output. Take a look at this: http://www.national.com/images/pf/LM317/00906338.pdf Notice how the output capabilities are 0mA when you have an input-output differential of 0? Now your wall wart wont be exactly 9V and that means your entire output capability is based on how "off" that wall war tis. That doesn't sound like a good situation to me at all. No matter which vreg you use you do not want to operate it at an input matching your output. You want it higher. If I were you and wanted 9V for this I would either use a 12V Wall Wart and a 9V regulator or just introduce some additional filtering on the Wall Wart like a decoupling cap from V+ to GND.

[Mark Hammer]

All 3-pin regulators I'm familiar with want at least 2vdc more at their input than they plan to deliver at their output.  So a 9v regulator wants at least 11vdc at the input.

Note as well that basic regulated supply designs tend to still have some ripple in their output, which will show up as hum.  So let the filter caps before and after the regulator share some of the heavy lifting!

[JKowalski]

I would like to point out that most 9V wall warts have 12VDC or more on the outputs - I have never, ever, seen any 9V rated wall wart with less then a 11VDC output. And I have gone through quite a few. This will work fine, if you double check every wall wart before you use it in conjunction with your "regulator box", but the safest bet would be to use 12vDC wall warts, as doitle said. The regulators will always have enough voltage to drop down to 9V, in that case.


However, you might want to consider building a spyder-type isolated power supply - so you have as many wall warts with regulation at the ends as you want, all in one box. I know you said you realise that, but I still highly suggest it.

[doitle]

These wall warts only supply higher than 9V when they are unloaded. When you put the regulator on there as a "load" it will drop down to supplying around 9V which will be too low for a 9V regulator. You can try this and just measure with a multimeter and if it works through some stroke of luck you are good... but I would probably try to nip this one before going on with any building or parts buying.

[Sir H C]

Low drop out (LDO) linear regulators are content and regulate pretty well with a couple hundred millivolts in to out.  They politely act like a series resistance when the input drops below the desired output. 

[trixdropd]

I would like to point out that most 9V wall warts have 12VDC or more on the outputs - I have never, ever, seen any 9V rated wall wart with less then a 11VDC output. And I have gone through quite a few. This will work fine, if you double check every wall wart before you use it in conjunction with your "regulator box", but the safest bet would be to use 12vDC wall warts, as doitle said. The regulators will always have enough voltage to drop down to 9V, in that case.


However, you might want to consider building a spyder-type isolated power supply - so you have as many wall warts with regulation at the ends as you want, all in one box. I know you said you realise that, but I still highly suggest it.

I have an ibanez wall wart and it's 9.0 volts to the "t"..

[JKowalski]

These wall warts only supply higher than 9V when they are unloaded. When you put the regulator on there as a "load" it will drop down to supplying around 9V which will be too low for a 9V regulator. You can try this and just measure with a multimeter and if it works through some stroke of luck you are good... but I would probably try to nip this one before going on with any building or parts buying.

I was talking about testing them loaded, powering my pedals. Always at least 11V, occasionally up to 13V.   

I'm not sure how much the regulator itself will load it down, but I can't imagine it would make too much of a difference.

I have an ibanez wall wart and it's 9.0 volts to the "t"..

Many wall warts built for pedals are much higher quality, I assume many of them actually have regulators in them. I am talking about your everday cheapo generic wall wart.



Maybe you guys have had better experience with the ones you have bought, but in the 10 or so $0.50 cent thrift store generic warts I have, none of them stray from what I said above.

[petemoore]

  An interesting alternative is to start with using a One Spot adapter.
  I'd say if you want the regulator in there, there it should be put.
  Finding a WW with the right polarity is first off.
  Finding one that rides around 11 or 12 volts shouldn't be a problem.
  I'm not sure what size voltage drop between input/output would make the regulator body start needing a heatsink.

[trixdropd]

I have an ibanez wall wart and it's 9.0 volts to the "t"..

Many wall warts built for pedals are much higher quality, I assume many of them actually have regulators in them. I am talking about your everday cheapo generic wall wart

I know. The Ibanez one goes for 9.99 at guitar center and at cost I was able to buy at 6.99. It was the cheapest i could find. I'd like to try a onespot though.

[newfish]

Excellent foor for thought guys.  Thanks!

My options here look like *not* putting a regulator in the box, and labelling it as '9v adapter', or including a regulator (and filtering etc) and labelling the box as '12v adaptor'.

Given theat the caps I'm using are rated at 16v, andf the LM386 will handle 12volts and upwards, even a 12v adaptor wouldn't break anything (unless it's *really* off and is giving 16 volts out - in which case the caps won't last quite as long).

Once again thanks for your answers.  My brain is now very well fed!