How important is a 100uf Cap and polarity protection Diode when using 1-Spot ?

[Derringer]

I've just been mimicking this procedure. Right on the DC input socket I put a 100uf cap across the rails as well as a 1n400x diode in a polarity protection orientation.

I'm not using batteries, I'm not using germanium transistors, and I'm only going to be hooking my pedals to a well regulated power supply.

Is there any reason to keep adding these two items or is it just extra for the sake of being extra?

[MikeH]

They're actually more important when using power supplies.  The 100 uf cap filters out noise from the power supply; it's not as important when using a battery.  And the diode is there to prevent damage if the wrong polarity powers supply is used.  It's a little more tough to connect a battery the wrong way.

[yeeshkul]

It happens to me quite regularly that i touch the battery snap with the battery turned wrong way

I would use a bigger cap for filtering power supply - 470uF as well as a little resistor in series (100-270 ohms) that helps to create a proper low pass filter.
Protection diode is a great idea, it doesn't cost anything and saves a lot!

Apart from the si diode across the power lugs, there is slightly more efficient way (used for example by Skreddy) - Schottky diode in series with the power lug. When you plug the power the right way, a small voltage drop will happen on the schottky (like 0.3V or so - unlike 0.65V on the standard si diode). When you plug the voltage wrong way, Schottky will stop it - unlike the Si diode in parallel that will short the voltage to the ground taking a massive current that way. This is always a bit dodgy - the current load on the si diode may be too big and the diode can burn before you realise there is something wrong ... and then good by semiconductors ....

[BAARON]

They're actually more important when using power supplies.  The 100 uf cap filters out noise from the power supply...

http://www.muzique.com/lab/filter.htm

[MikeH]

No doubt it depends on many things; One example I can give personally has to do with a zvex power plate.  The power plate has the typical 100uf cap in parallel + small resistor in series connected to the battery snap.  When I used a one spot 9v snap to barrel jack adapter (drilled a hole though the bottom of an extra enclosure, my own home made rigged power plate) for a seek wah, it was VERY noisy, but with the power plate is was much quieter.

I guess the real answer would be you can just add it as needed, but I think it's easier to just put it in by default.

[Lurco]

switchmode supplied circuits can benefit from 100n and a ferrite bead in the places suggested for the 100uF and small resistor for conventional supplies!

[yeeshkul]

I find the article at http://www.muzique.com/lab/filter.htm a bit misleading. It looks like you have 1000uF filter cap in any wallwart (which is by far NOT true - the golden rule says: use 1000uF for each 1A of the current draw) and so that you are doing funny thing adding 100u-470u in parallel on the PCB side, making 1470uF filter.  I disassembled a good few of them and it really varies between 470-1000uF. The function of the filter cap on the circuit side is not to make the wallwart cap larger but:
1. there is about 1-2m of cable (between those two caps) that always provide certain impedance (and thus voltage drop right on the cable caused by the current running through). The current draw is usually not consistent, so that it provides a voltage ripple right on the cable - there goes your cap. You will not help this by adding a fatter cap on the wallwart side.
2. in case of the circuits like FF or TB, the cap can help with the unwanted "in phase" feedback between the trannies

EDIT: adding 10-100n in parallel to the cap on the circuit side is quite a good idea too - as it was mentioned few times at this forum. Small caps work better with high frequency noise - the little cap then helps the big cap where the big cap is clumsy