I need a diode, can you tell me which one?

spin · **Posted:** Sat Oct 29, 2011 3:30 pm

years ago this kid gave me a dd-3 to fix. He told me it works off the battery, but not the 9v jack. This kid was a spoiled brat and had any dozen number of pedals at a given time, my assumption was he connected a reverse wired adapter from some off the wall pedal. I popped it open and quickly found a blown diode (D9) physically close to the jack and tied to the ground. Well, 8 years later after deciding to switch from my rack setup to pedal based i'd figure i'd give it a fix. only problem is i can't figure out what the diode is, i wrote down 1n4004 when i took it apart back then. When i look at the diode now, i'm not so sure thats what it says, as its burnt to hell and i was just clued in on my now eyesight problem. Can anyone verify this number and does anyone have one lying around? i can't bring myself to make an order somewhere for such a small part. i will paypal.

Stephen · **Posted:** Sat Oct 29, 2011 4:32 pm

If it's just a simple reverse polarity protection diode any 1N400x series diode will work.

guitarmageddon · **Posted:** Sat Oct 29, 2011 4:53 pm

There are a couple of service manuals with parts lists and schems HERE
They might be of some help...

spin · **Posted:** Sun Oct 30, 2011 10:03 am

word, thanks guys.

spin · **Posted:** Tue Nov 01, 2011 10:17 am

I picked up some of the 1n4004's from jameco just to be on the safe side and use a like numbered part. Had to order 10, looks like the traveling parts box picks up the other 9 unless anyone else could use them.

powerpopguy · **Posted:** Tue Nov 01, 2011 1:43 pm

While we're on this subject, can I add a diode at the DC jack on circuits without polarity protection? Like this:

Anyone else doing it like this at the jack?

(I don't use battery snaps, so I'm not concerning myself with that..)

Stephen · **Posted:** Tue Nov 01, 2011 1:56 pm

That will work but not as well as a series connected diode. A reversed diode like the one in your pic will work but it is still possible (and likely) to take out an op-amp if you plug in a reverse polarity power supply.

powerpopguy · **Posted:** Tue Nov 01, 2011 2:11 pm

Thanks Stephen. Does a series-connected 1N400X diode eat any more voltage than the .7v I'm presently expecting?

Stephen · **Posted:** Tue Nov 01, 2011 2:43 pm

Check the rated Vf on the data sheet for the diode you're using. In most cases it will vary between .7 and 1V

ChrisM · **Posted:** Fri Nov 04, 2011 4:10 pm

Stephen wrote:

That will work but not as well as a series connected diode. A reversed diode like the one in your pic will work but it is still possible (and likely) to take out an op-amp if you plug in a reverse polarity power supply.

Yep

Only downside of the series diode is the Si voltage drop (~0.6V). Usually not a big deal but in 9V designs that's a considerable amount of voltage.

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I need a diode, can you tell me which one?

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