1N4001 similar diodes

[alexisdroso]

Hey , I have a couple of BOSS pedals that use the 1N4001 diode for reverse voltage protection and I'm considering changing them with 1N5408 diodes which have 3A Io instead of 1A that the 1N4001 have. Do you advise against it or not? I know that the 1N5408 are quite bigger than the 1N4001 but they fit in the pcb without any problem. Any suggestion would be greatly appreciated.

[GibsonGM]

They look like they certainly would do the job, tho as you say will take up more precious real estate on your board.   Why would you need to change the ones that are there, if they are OK? 

I'd use it if it was practical on a NEW BUILD, if it was all I had; but then, I keep like 200 1N4001's on hand so I don't have to worry about this!  I wouldn't bother replace working 4001's tho.

[Kevin Mitchell]

This mod would do absolutely nothing for. If it ain't broke... don't fix it.

[R.G.]

Hey , I have a couple of BOSS pedals that use the 1N4001 diode for reverse voltage protection and I'm considering changing them with 1N5408 diodes which have 3A Io instead of 1A that the 1N4001 have. Do you advise against it or not? I know that the 1N5408 are quite bigger than the 1N4001 but they fit in the pcb without any problem. Any suggestion would be greatly appreciated.

My immediate response is why?
If it's a series diode (and I don't think it is, Boss uses the reverse shunt method below) it will conduct normally, and your pedal should not need more than 1A. I hope. 

If it's ta shunt reverse-protection diode, it's not intended to conduct current in normal operation at all. It's there in case you hook up a reversed power supply to the pedal. When that happens, the diode conducts and holds the reverse voltage down to one diode drop, and protects the parts on the pedal power supply.

The purpose of that diode is not to be able to conduct unlimited current forever, it's there to prevent a disastrous meltdown of the pedal PCB for a short time. Except in very limited circumstances, it does this very well. A 1N4001 and its other 1N400n brothers can conduct 1A continuously, but the peak pulse current is rated for 30-45A for short peak currents. It's a good short term protector.

What it's not good at is being a long term protector, at least not by itself. If you have an unspecified DC power supply hooked up to your pedal with reverse voltage, what happens to the protection diode depends on what that power supply does. If it is a good, well designed power supply, it will limit its current to something reasonable, like maybe 1-2A. This limitation means that a 1A 1N4001 will protect the pedal forever. I've actually tried this, hooking up [a power supply known to be a good design] to a pedal with a reverse diode for a couple of days with the voltage reversed. No damage to either the power supply or the pedal.

If the power supply has an unlimited current, it will generally fry the reverse diode to a short circuit, and then either melt the solder joints or the power wires.

A disaster the reverse protection diode can't protect against is hooking up an >>AC<< power supply to a pedal. The AC causes the reverse diode to conduct a lot of current reversed, and overtemps the diode, much like the unlimited current DC supply, but an AC power source will always be reversed half the time. So it overheats and shorts the diode, then overheats the solder joints on the diode, which opens, and then the pedal circuits are treated to death by AC. Of course, putting in a bigger diode just lengthens the time before death. It's possible that you could put in a diode big enough to prevent this by causing death/limiting on an AC supply, but I wouldn't suggest that either.

In any case, simply changing a 1N4001 for a bigger diode isn't the best move. Providing for proper protection by other means and to cover other circumstances would be better. As would simply not hooking up reverse or AC power supplies to a pedal.

[Paul Marossy]

A disaster the reverse protection diode can't protect against is hooking up an >>AC<< power supply to a pedal. The AC causes the reverse diode to conduct a lot of current reversed, and overtemps the diode, much like the unlimited current DC supply, but an AC power source will always be reversed half the time. So it overheats and shorts the diode, then overheats the solder joints on the diode, which opens, and then the pedal circuits are treated to death by AC.

Hence the "I bought a dead blah blah off ebay and the diode is fried at the power jack, can it fix this, will it still work?" questions on various forums. Sometimes people get lucky and sometimes it truly is a disaster.

[Ice-9]

Leave it as it is, nothing to gain from this at all.

[ElectricDruid]

As others have said, nothing to be gained by making this change. Don't bother.

That said, if you have a dead 1N4001, you can replace it with other diodes in the series 1N4002, 1N4003, 1N4004 etc. They all share a datasheet, and the difference between one and another is the maximum reverser voltage, all the way from "sufficient" up to "beyond ridiculous". For example:

https://www.vishay.com/docs/88503/1n4001.pdf

HTH,
Tom

[R.G.]

DANGER!! 50,000 OHMS!!