Powering pedal Question.

[Izzy]

Hi I wanted to know what does the Diode and Capacitor do in that powering?

Is it completely necessary to include that caps and diode there? Does it make any impact on sound?

Please answer these question.

[finkfloyd]

I'm no expert at all, so correct me if im wrong, but i think that as a whole is a voltage divider, but the diode is for reverse polarity and seems to be pointing the wrong way for the purpose, and the 100uf cap to ground is for anti-hum, except i would of used 470uf for that purpose also

Im sure someone can give a better insight than I

[zyxwyvu]

The diode is indeed for reverse polarity protection. In the event that the battery or power supply is connected in reverse, the diode will short it, taking all the current, and protecting the other components from reversed voltage.
The capacitors are for for filtering hum out, and also they can help supply power if one component draws a spike of power (though non-electrolytic capacitors are better for that). If you only use a battery, the capacitors won't do much at all, and if you only use one polarity of wall power, and no batteries, you probably don't need the diode. They can be left out, but it is probably a good idea to keep them.

[Peter Snowberg]

I always like to have a protection diode in there, but I prefer the series approach where the diode sits in-line with the positive battery connection. If you reverse the polarity with the series configuration, no power will flow and nothing is damaged. In the schematic above, the diode shorts the power to ground when polarity is reversed which is fine for a small reversal but the diode will eventually fry if the supply is left on and you have enough current available. Once the diode is fried it may open which will let the power flow in the wrong direction.

If you use a series diode, that diode becomes part of the power supply impedance and adding a big electrolytic cap after it will reduce the total supply impedance.

[darron]

I always like to have a protection diode in there, but I prefer the series approach where the diode sits in-line with the positive battery connection. If you reverse the polarity with the series configuration, no power will flow and nothing is damaged. In the schematic above, the diode shorts the power to ground when polarity is reversed which is fine for a small reversal but the diode will eventually fry if the supply is left on and you have enough current available. Once the diode is fried it may open which will let the power flow in the wrong direction.

If you use a series diode, that diode becomes part of the power supply impedance and adding a big electrolytic cap after it will reduce the total supply impedance.

will your method drop the voltage on the output of the diode by a small amount? i'd be inclined to agree with you on that.

i suppose i could do a test...

[zyxwyvu]

will your method drop the voltage on the output of the diode by a small amount? i'd be inclined to agree with you on that.

Yes, with that method you won't get full battery voltage through the diode. There will be a drop of about .6-.7V for a regular silicon diode, for example. It works the same way as a clipping diode's voltage drop.

[Peter Snowberg]

Yes, Darron, you are correct.

I use Schottky diodes to lower the voltage drop to ~0.3V so it's not been a problem for me (so far).

Favorite Schottky: 1N5818 (1 Amp with a Peak Inverse Voltage of 30)

[Izzy]

So that means I can use any diode?
Can I put 1 SI diode? or is it better to put 2 Si diodes in series like you said?

[Peter Snowberg]

Yes, you can use any diode, but regular Si diodes will drop the voltage twice as much as Schottky diodes will. In many circuits that may not matter too much, but I prefer to try to keep that extra 0.3V.

You only need a single diode for either shunt (from power to ground) or series (in-line with the + supply) protection and you only need one style of protection on a circuit. I still use Schottkys for shunt protection (when replacing burned out diodes) because they'll conduct before the parasitic diodes or the input protection diodes in opamps.

[Izzy]

hmm ok then I will put 1 - 1n4148 diode shunt to ground. That should just drop 0.3V right?

[petemoore]

Favorite Schottky: 1N5818 (1 Amp with a Peak Inverse Voltage of 30)
 Never heard of it. Till Now...
 Nice piece !!'  
 After all the 'whappenned to my pedal when I reverse polarized the PS?' posts and personal experiences, I began routinely installing 1n4001 or bigger Si types. the few minutes it takes for installation may equate easily to elimination of 'long winded', troublesome repairs.
 For batteries, that '.6v' can matter, but batteries are easily reverse polarized too. After a few 'reversals' I became more familiar with the non wire end of the battery clip being for the small + post of the battery, and installed the RP diodes anyway.
 .6v...why? when you can simply choose a nice sturdy' 1N5818 that only drops .3v
 I find it a bit surprizing this is the first I've heard of a Schottky for RP Protection. Nice new mod to try...lol.
 
 
 

[petemoore]

1n4148 diode shunt to ground
  Measure it with a DMM or view data sheet, I thought Si's like that are around a .6v drop.

[Izzy]

sorry I mean 0.6-0.7.
So Can I use it?