how to add a power supply filter cap?

[plexi12000]

i've been lookin at a couple pcb layouts that i thought about building.  but they dont have a power filter incorporated in the layout.

basically...i need the positive lead of the capacitor to connect to the 9v + (NPN circuit) and the neg. lead to ground.

that's about it, right?  thank you- happy thanksgiving.

[Joe]

You probably won't need a very large one if using a battery or regulated power supply. Maybe 100uF tops?

[Cozybuilder]

For external power supply I like to use the following: 1n5817 Schottky for reverse polarity protection, anode to the DC power supply in, cathode to a 1/4W 47 ohm resistor, then 100 uF cap to ground, and a 100nF cap to ground. This setup basically filters off everything above 32 Hz- which I designate as V+ on schematics.

[plexi12000]

For external power supply I like to use the following: 1n5817 Schottky for reverse polarity protection, anode to the DC power supply in, cathode to a 1/4W 47 ohm resistor, then 100 uF cap to ground, and a 100nF cap to ground. This setup basically filters off everything above 32 Hz- which I designate as V+ on schematics.

wow....that's pretty elaborate. well...to me it is, anyway! -lol   

let me ask the dumb beginner questions and see if i understand your schematic (and thank you for posting it)

the diode and 47r are in series?  and you'd just stick them in the supply line? (and caps to grnd)   hope you understand what i'm asking 

[Kipper4]

Yep that simple plexi

[Gargaman]

I have seen this setup frequently on many layouts:
- diode for reverse polarity protection;
- big cap for power filtering;

In this configuration you get a low-pass filter, set by who? 100uF and 47R?
I use this http://www.muzique.com/schem/filter.htm
and came to 33,9Hz, is that allright?
I wonder what the 100nF do.

[Joe]

If I'm not mistaken, the ceramic 100nF has a lower impedance at higher frequencies than the aluminum electrolytic is capable of, improving filter performance.

[davent]

And tap off for your LED before the 47r resistor as the LED can be the biggest current draw in a pedal dropping a good chunk of voltage across the 47r resistor. (Again that will depend on the LED you're going to use.)

dave

[Cozybuilder]

All of the above. I usually put the LED & its resistor between the diode and 47R, as Dave points out. Water clear blue 3mm & 47K give a bright indicator, and draws little current.

[PRR]

> that's about it, right?

The capacitor is like a 100 pound weight.

If you tie 100lbs to your hand, it won't shake fast.

If you tie 100lbs to my tractor's 4,000 pound bucket, it won't slow down at all.

Some crappy power supplies have high-power crap. 100uFd don't do much.

The resistor is like tying a stick the size of your arm to my tractor bucket, and the 100lb weight on the end of that arm. While the tractor can still jerk its bucket, the flex in the arm/stick allows the 100lb weight to stay pretty steady.

The diode is a frill, until you connect power backward. Stuff happens, and out stuff may not not like backward power (smoke).

The 0.1uFd cap is IMHO a frill, not essential in small audio-only work. It may be vital if there is clocked data involved (BBDs, digital LFOs). It isn't much money or space.