Snippet: power filtering and polarity protection

[earthtonesaudio]

This info has been around for a while (GEOFEX) but I thought I'd make a picture anyway.

...Not sure if the second Zener is really necessary.

[oskar]

Hey, I know that movie!   
http://www.imdb.com/title/tt0093507/

[R.G.]

What's the 330 ohm resistor for?

[earthtonesaudio]

What's the 330 ohm resistor for?

If you use a 1-spot, it serves no function except to waste power.   

...But if you're like me and collect cheapo unregulated (read: noisy) power supplies, it serves two functions.  First, it reduces hum by providing a low pass along with the 100u capacitor.  Second, it limits current to the 9.1V zener.  Most of my "9V" unregulated supplies will put out 12V or more when powering a light load like a fuzzbox.

I was trying to make a sort of "universal" power section.  The Zener is less efficient than a low-dropout regulator when using a wall wart, but if you use a battery, it's more efficient.  Ah, compromises.

[sam_801023]

This info has been around for a while (GEOFEX) but I thought I'd make a picture anyway.

...Not sure if the second Zener is really necessary.

I want to ask that what does the p-MOS stand for ? P-channel Mosfet ?
what are the connection of those pinouts ?

[earthtonesaudio]

Yes, "P-MOS" means P-channel MOSFET.  The arrow indicates the Source, the terminal connected to +Vin is the Drain, and the terminal connected to the 1M resistor is the Gate.

The pinout will vary depending the specific part you use.

Good luck!

[R.G.]

I'd probably use a low drop out series regulator instead of a 330 ohm and a 9V zener. I don't like shunt regulators.

330 ohms will choke the amount of current you get a lot. 330 ohms is literally 330 volts per ampere, or 0.33V/ma. A pedal using 10ma will drop the output voltage by 3.3V down to 5.7V if you have 9V into the thing. With more current, it gets worse.  A LDO regulator will follow the input voltage by saturating down to about 0.2V less than the input voltage at everything below 9.2V, and will hold it at 9V in the face of inputs above 9V.

[Cliff Schecht]

I'd probably use a low drop out series regulator instead of a 330 ohm and a 9V zener. I don't like shunt regulators.

330 ohms will choke the amount of current you get a lot. 330 ohms is literally 330 volts per ampere, or 0.33V/ma. A pedal using 10ma will drop the output voltage by 3.3V down to 5.7V if you have 9V into the thing. With more current, it gets worse.  A LDO regulator will follow the input voltage by saturating down to about 0.2V less than the input voltage at everything below 9.2V, and will hold it at 9V in the face of inputs above 9V.

Not to mention the Zener voltage varies all over the map with respect to the amount of current the diode is shunting. Even for low precision, low current draw situation I really prefer to use the classic TL431 reference (bandgaps rock!). There are better ways of getting simple regulated power than using a standalone shunt Zener configuration is all.. Take a look at this simple classic: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/emitfol.html#c2

[earthtonesaudio]

Well sure, if you want to be all efficient, good-performing, and simple about it, go ahead.  Knock yourselves out with your fancy LDOs.

[mr.adambeck]

has anyone made a vero layout for this (or anything similar)?  Thanks!