TUTORIAL All About Diodes - A Gathering of Various Resources Out There

[BuddytheReow]

Hey All,

I wanted to do a write up about diodes: theory behind them, what they do, different types, how they interact with circuits, clipping types, voltage drops, etc. In doing some final research I realized there is a TON of info out there specifically related to guitar pedals. Rather than copy/paste others' work and diagrams I decided to create a depository of what I think are a lot of very good sources out there in their various formats. A little blurb about each link will be my contribution.

Introduction to Diodes And Rectifiers - Electrical theory from AllAboutCircuits. A great educational resource out there and something I stumbled upon with my self learning. Theory will help you troubleshoot, modify, and create your pedals! Whether you know zero theory or need to brush up on something, this will definitely help

The Different Types of Diodes - Coda Effects' write up which sums up pretty much what I wanted to write here. It covers basic theory, diode types, clipping, and polarity protection

A Brief Hobbyist Primer on Clipping Diodes - A great article on Guitar Pedal X. A touch of theory, hard vs soft clipping in circuits and some famous pedals that use either, symmetrical vs asymmetrical clipping, and diode types with forward voltages.

LED Polarity - PedalPCB's write up how to install diodes on your boards. A little older (2019) during the transition from older boards to the newer ones. This will help save you some troubleshooting!!

What's All This Stuff About Germanium Diode Leakage?- @Chuck D. Bones write up of germanium diodes done over this summer on here. Know your theory first, but a phenomenal write up.

How To Build Guitar Pedals - Clipping Diodes Compared - Fuzzlord Effects YouTube video explaining clipping diodes for distortion. Some theory, a look through an oscilloscope at their waves, and sound bytes of clipping types in one of his pedals .

What is Diode Clipping? | Too Afraid To Ask - CSGuitars YouTube about hard/soft clipping to the average Joe. Also a plug for a Walrus Audio OD pedal which you can hear the difference in clipping types.

Diodes - Mark Hammer's small write up on diodes and whether you can swap out silicons for germaniums and vice versa. If you've read everything else above this will be a little repetitive, but explained in a different way.


If anyone has any other great resources out there please share them here!

Thanks,

BuddyTheReow

 

[fig]

Wow, the Diode Equation is a spoonful! It may take me some time to apply this equation. I have an app with many of these algorithms included as functions, which is handy but not conducive to actually learning / understanding the equation.

Thanks for sharing!

 

[BuddytheReow]

Wow, the Diode Equation is a spoonful! It may take me some time to apply this equation. I have an app with many of these algorithms included as functions, which is handy but not conducive to actually learning / understanding the equation.

Thanks for sharing!

The more you learn the better you’ll build! I’m just trying to pass on my knowledge.

 

[fig]

Now I remember where I read it!

What's All This Stuff About Germanium Diode Leakage?

Like Germanium transistors, Germanium diodes are leaky. They behave like they have a resistor in parallel and in many cases, that resistor is less than 50K. The higher the leakage, the lower the resistance. Two questions that keep popping up are: How much leakage is too much? How do we...

forum.pedalpcb.com

 

[finebyfine]

Incredible compilation! Thank you!

 

[maxamendel]

necroposting

what about diodes that look like germanium but test around .7v?

I have a couple with two black bands and a batch of small clear ones with the single blue band. But they test at .7v. Are they in fact silicon? does the package mean anything significant if im sorting 50 diodes and I have a GM328 tester?

what matters besides drop voltage? whats the capacitance value do? Whats Ir?

uhhh. I read once that the knee is different for different diodes, but the only real way to test that quality is with an oscope. is that true?

thank you all. The internet is a beautiful thing.

 

[PedalBuilder]

necroposting

what about diodes that look like germanium but test around .7v?

I have a couple with two black bands and a batch of small clear ones with the single blue band. But they test at .7v. Are they in fact silicon? does the package mean anything significant if im sorting 50 diodes and I have a GM328 tester?

Germanium is much more temperature sensitive, so you can take advantage of that to figure out whether they are germanium or silicon. First, put the diode in the tester, and wait a minute for the heat of your fingers to dissipate and the diode to return to ambient temperature. Test the diode and write down your measurement. Next, old the diode in your hand for a minute, and then test it again. If you get significantly different results, the diode is germanium.

uhhh. I read once that the knee is different for different diodes, but the only real way to test that quality is with an oscope. is that true?

No. Other ways include using a curve tracer like a DCA75, or you can do a rough approximation/two point “curve” using a multimeter or other device that tests the diode Vf at a different current than your semiconductor tester, in addition to using your semiconductor tester.

 

[jwin615]

You can plot a diode with an oscope, but it's not ideal.
You need a small ac source and a CLR. Plot voltage to one axis and current to the other.
But again, not ideal or all that accurate.
Check out the octopus curve tracer project. Again, not the best tool for the job but cheap and easy. Where a scope based curve tracer shines is for on board troubleshooting/repairs. Ala a huntron tracker.