Clipping Diodes

Frequent question abouts LED and other types of diodes.
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holio cornolio
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Post by holio cornolio »

So when choosing clipping diodes, what values on the datasheet are the one sto be looking at? Forward / Reverse voltages?
I have literally NO idea what I am doing.

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NickS
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Post by NickS »

Depends what voltage you want to clip to.

Forward voltages for small-signal diodes are typically 0.3V for Germanium and 0.6-0.7V for silicon. LEDs vary but can be around 2.5V If you want to clip to these levels, use them in parallel.

If you want to clip to higher levels you can use parallel chains of series diodes.

Alternatively, use the reverse voltage (Zener voltage) of Zener diodes or the breakdown voltage of transistors' B-E junctions. In this case the diodes need to be in series to avoid clipping at the forward voltage.

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Post by JiM »

You can also have a low threshold with Schottky diodes.
These can even clip a passive guitar signal, as in the "Black Ice overdrive"
http://www.stewmac.com/shop/Electronics ... drive.html
http://www.projectguitar.com/tut/blackice.htm

And you can play with asymetrical clipping by having different type or number of diodes in each back-to-back branch, hence clipping positive and negative alternances at a different voltage, and generating more even harmonics ...
I only give negative feedback.

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Post by Greg »

Keep in mind that there's more to clipping diode choice than forward voltages.
Different types can have a fairly major effect on tone as well.
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clinchfx
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Post by clinchfx »

Greg_G wrote:Keep in mind that there's more to clipping diode choice than forward voltages.
Different types can have a fairly major effect on tone as well.
I completely agree Greg. The important characteristic is the forward current/forward voltage graph. Unfortunately, the graphs in data sheets for most popular diodes have a scale that is too large to provide any real detail in the 0-5mA forward current region. but silicon diodes such as 1N914 tend to have a larger non-linear region than Germanium or Schottky diodes. Non-linear conduction curves should create smoother sounding clipping than linear curves. I've found that series combinations of silicon and Schottky diodes sound better than silicon alone, even though you would expect the curve of the silicon diode to dominate.

Peter.

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Post by Spazzmatazz »

soo... better silicon??

wich one??
what improvements you've done?

I'm thinking to make a passive box with a rotary swicht for testing diode combination and diferent guitars.

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Post by Electron Tornado »

Spazzmatazz wrote: I'm thinking to make a passive box with a rotary swicht for testing diode combination and diferent guitars.

I don't worry much about the specs on the data sheet as the real test is your ears. I have enough diodes around to be able to try different combinations as well. For experimenting with clipping diodes I use a couple of wires with alligator clips for quick changing. This also allows me to quickly test diodes in both hard and soft clipping settings.

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Post by Spazzmatazz »

which diodes work? which doesn't?

schottky only?

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clinchfx
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Post by clinchfx »

Electron Tornado wrote: I don't worry much about the specs on the data sheet as the real test is your ears.
Agreed - Ears are the best test instrument for guitar effects. Because I've been trained to use data sheets, I still like to try to correlate the specs with tone, but you don't always get what you expect. :oops: :wink:
Spazzmatazz wrote:which diodes work? which doesn't?

schottky only?
I like the tones I've heard with a 100mA Schottky in series with a normal silicon diode that is similar to a 1N914, in the feedback path of a TS type circuit. These were SMT dual diode packages and I used only one diode from each package. The Schottky was a BAT754S and the other was a BAV99.

The bottom line is that you should try as many different combinations of power or signal diodes, LEDs etc. as you can think of. You can also use one junction of a transistor as a diode, or connect the base to the collector and use the emitter and collector leads as a diode.

Peter.

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Post by P1NkY »

clinchfx wrote:
Greg_G wrote:Keep in mind that there's more to clipping diode choice than forward voltages.
Different types can have a fairly major effect on tone as well.
I completely agree Greg. The important characteristic is the forward current/forward voltage graph. Unfortunately, the graphs in data sheets for most popular diodes have a scale that is too large to provide any real detail in the 0-5mA forward current region. but silicon diodes such as 1N914 tend to have a larger non-linear region than Germanium or Schottky diodes. Non-linear conduction curves should create smoother sounding clipping than linear curves. I've found that series combinations of silicon and Schottky diodes sound better than silicon alone, even though you would expect the curve of the silicon diode to dominate.

Peter.
I've always thought germaniums produced clipping with a rounder knee at the conduction point, leading to a softer clipping, albeit at a much lower output.
Don't silicons like 1N914s pretty much chop off the tops of the waveform like a razor blade, leading to a harder clipping, with more high frequency content and higher output? Aren't they originally designed for fast switching applications?
I've always had to use caps to sort of "tame them down" a bit. :block:

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Post by Electron Tornado »

clinchfx wrote:
Electron Tornado wrote: I don't worry much about the specs on the data sheet as the real test is your ears.
Agreed - Ears are the best test instrument for guitar effects. Because I've been trained to use data sheets, I still like to try to correlate the specs with tone, but you don't always get what you expect. :oops: :wink:



The bottom line is that you should try as many different combinations of power or signal diodes, LEDs etc. as you can think of. You can also use one junction of a transistor as a diode, or connect the base to the collector and use the emitter and collector leads as a diode.

Peter.

It would be interesting to see a table with specs for various diodes to do a comparison.

I agree about trying different combinations. To some extent, you don't always know what's going to sound best in a particular application. That's part of the fun of DIY, IMO. To my ears there are only a handful of combinations that sound appreciably different, however there are quite a few more where the differences are subtle. In the end, it really depends on what appeals to the builder's ears.

What would be great is if we could some up with a standardized set of descriptive terms for different sounds of distortion.

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