Tonepad Pedal Power

[chromesphere]

Hey guys,
I was thinking about building something a bit different and was looking at the tonepad pedal power.  I have a 12vDC powerpack here i thought i would put into service with an LM317 and thought tonepads pedal power would be a suitable project.  But i noticed that his design uses a 12vAC not DC.  Would i be right in guessing that i can still use the 12vDC powerpack and just leave out the diode bridge?  Or even build it WITH the diode bridge as its jst there to rectify the ac signal?  Anything else i should be concerned about?  I've never really worked on ANYTHING power related.
Cheers!
Paul

[WaveshapeIllusions]

You would want to leave out the diode bridge as it will introduce losses. The 12VDC output could probably just go straight into the regulator. All that would be needed would be filtering.

[chromesphere]

You would want to leave out the diode bridge as it will introduce losses. 

Oh yeah forgot to mention that,  thanks for confirming!

What about the output current supply of the powerpack?  The one im looking at using says 1.2amps.  Im assuming if i actually hit that (unlikely) the powerpack will probably have some sort of internal protection?  The LM317 is capable of 1.5amps according to the datasheet, so the powerpack would be the weakest link i guess you could say.  Im assuming this will all be fine though.

Paul

[WaveshapeIllusions]

Yeah, it should not be a problem. Whatever the regulator supplies though, the power pack will need to give more. It should be a stable 12V (perhaps higher unloaded) so the regulator will always be dropping ~3V. The power pack will have to supply the extra current there, so I would not load the regulator with more than 1A.

If you don't mind running your effects higher, they can probably run straight off the pack. 12V isn't much higher and most things shouldn't be damaged. An LM386 might be a bit unhappy if the supply ends up much higher than that, but otherwise everything would be fine.

[chromesphere]

Thanks again waveshapeillusions.

The main reason i was thinking of building this is for noise filtering.  I thought using a regulator (the LM317) would cut out the power pack noise (like a voodoo labs power supply).  Is this correct?

Paul

[WaveshapeIllusions]

It should cut down in noise quite a bit yes. If the power pack uses a switchmode supply, there may be some noise coupled in. Usually the switching frequency is rather high, so the regulator could be too slow to catch it. Good filtering is the best solution for that. Rod Elliot's site has a capacitance multiplier/regulator that would cut almost all supply noise out. It's a bit more effort though, and realistically standard bypass caps and a regulator will do just fine.

Chances are though, the power pack is already regulated. If its a switchmode it almost definitely will be. I'd say see how it works out with just the pack first. If there are any noise issues or oscillations (I've seen some HF switching noise coupled through supply) a regulator and filtering will be necessary. Otherwise it shouldn't be an issue. The losses the regulator introduce will make the supply work harder at high loads though.

[chromesphere]

Its a powerpack from a router, just a random / spare one lying around, no idea if its switchmode or not, ill have a look at it tomorrow at work.  Thanks for the info waveshape!
Paul

[duck_arse]

if it weighs "heavy", it will probably have a tx inside, and is linear. if it weighs "nothing", probably switchmode, no transformer.

[chromesphere]

Yeah, its pretty heavy   Don't use it?
Paul

[waltk]

Don't use it?

No, it's good.
Heavy = transformer = you don't have to worry switching noise. 

You can tell whether it's already regulated by testing the voltage output with no load.  If it's labelled at 12V, but puts out more than that with no load, then it's not regulated - perfect use for a 317.

[chromesphere]

I think it could actually be switched (although its hard to find any details on it: OEM model AD-121A2E).

Well, i might just try this one anyway.  Hopefully there wont be much noise from it after i add the regulator.

Paul

[duck_arse]

chromo, didn't you buy an oscilloscope of some description recently? you could just look at the dc output with that, ac coupled, on the most sensitive input setting (with x5 gain if you have it). that might show you something, and you could compare the input to the regulator output.

[chromesphere]

Hah...of course Didn't think of using the oscilloscope Ill check out the output on this thing and see if its noisy.  I've ordered the parts for the regulator anyway so it might be interesting to see the difference!
Paul