How do they DO that????

[343 Salty Beans]

I'm probably in way over my head, but here's my question:

The Aphex punch factory can use any power supply that's 5-12V AC, or 7-17V DC, any polarity. I can figure AC, I've used a few full-wave rectifier diode bridges before and understand how they work. I can understand charge pumps and voltage-controlling ICs. But how do they make the polarity reversal okay with a DC line? I've been thinking about it all day, and I can't figure it out with just diodes. Is there some transistor switching involved?

PS: here's the backside of an APF for reference.

[slacker]

You can do it because a full wave bridge rectifier will put out positive DC whether you feed it AC or DC of either polarity.
I think the diagrams on this page explain it http://en.wikipedia.org/wiki/Bridge_rectifier the ones with blue and red lines.

[Sir H C]

It is using a switching supply internally.  Assume it is a buck-boost design.  So you first just have (as stated) the diodes and first filtering capacitors to make a rough DC voltage, then with the switching regulator you can create the desired voltage (even if the desired output voltage is higher than the input voltage). 

[Meanderthal]

 Of course this leads to the question- has anyone designed a diy 'universal' wart input for a pedal? Nah, nevermind, too much trouble... 9v rectified power supply is easy enough, although it might be cool to include a rectifier so you can use just any old cheap wart laying around if you're in a bind...

[Sir H C]

A lot of laptop computers use a universal supply that without any user changes can run on any AC supply from ~100 volts to 240. 

[QSQCaito]

and 50hz or 60hz

[R.G.]

It's not really all that difficult.

As noted, a diode bridge makes all voltages look DC and the correct polarity. When you rectify to DC, you mostly don't care what frequency the power line was. That's only an issue for power line frequency transformers.

Once you cross the bridge to doing a switching power supply, it's fairly simple to do a 2:1 range on input voltage and keep the same output voltage. This used to be a difficult thing to do, but modern ICs have been developed which make a step up/down regulator possible.

Switching power supplies with high gain audio effects will always carry the possibility of noise problems, and will require careful design of distribution, decoupling, and grounding to keep this out.

[Sir H C]

And they keep making the switching speed higher (1 MHz plus for some) that you are so far removed in noise that often you do not have to worry much.

[Hiwatt25]

Would anyone be willing to grab a schematic with a "pulldown" resistor or resistors in it as described in the Geo article referenced above and circle them for me?  I read the article but I have a hard time seeing it in my head and the discussion above regarding where to put the resistor (before/after switch) kind of confused me.  I'll give you a nickle.

Gracias

[Meanderthal]

 Heh- you musta meant to ask the Drop down resistors thread...

[Hiwatt25]

Oh man, I suck lol!