reverse polarity protection - fixing damage from reverse voltage

[okuzster]

hi all,

i damaged my tube screamer with reverse voltage, schematics is at the bottom, and found that info below it, so it's most likely my ic fritz, will try to replace it soon.

more important thing i wanna add reverse polarity protection and i am a bit confused. after a little search i saw lots of way for it but have no idea how they differ or which is best for me, anyone can help me on that? and i believe it's all same for all pedals, am i right?

Reverse voltage survival is different. If the pedal has no polarity protection, reverse polarity is a death sentence for every IC on the board. This happens in milliseconds to a few seconds. Longer reverses will kill all of the electrolytics. Often the diodes and transistors will survive this. Sometimes they will be damaged, often not. Ordinary R's and C's usually survive. If the pedal has polarity protection, everything depends on what kind and how good the protection is. The common reversed-diode protection is really only good for short periods of reverse connection to a battery or adapter. If you leave a reverse-diode protection pedal connected to a strong battery or AC adapter for a long time, it will eventually burn out the diode or other protection parts. Then you have no protection, and you're back to the first situation above, replacing ICs and electrolytics.

[GGBB]

The differences between various techniques boil down to what kind of protection they offer, what drawbacks they have, and how well they do the job. You could write a short book on that. The reverse diode protection RG mentions is probably the most common in DIY pedals, and is nothing more than a diode connected anode to ground and cathode to power. Easy to implement or add to an existing pedal; no drawbacks; minimal protection. It protects from occasional temporary short polarity reversal only.

An alternative is to connect a diode in series between the power supply and the circuit power in. This is more robust protection, but is slightly trickier to add to a circuit and has a disadvantage in that it lowers voltage to the circuit by the forward voltage of the diode. If you use a Schottkey diode like a 1N5817 you can minimize the voltage drop problem so that most pedal circuits won't care.

Beyond those two, things get more complicated. Either one of those two is perfectly suitable for a DIY pedal that is going to be used by the builder and therefore doesn't need a bullet proof solution.

[PRR]

Replace the chip. Add a series diode.