Choose Clipping Diode

[Rebel_88]

Hi all, i want to ask you a way to choose a clipping diode. I mean what I have to read on the datasheet to choose my favourite diode.
Because i can't understand the difference between an 1n4148 and 1n914 or other because they have similar Forward Current, the same Power Dissipation and so on. Someone uses also light diode and i saw on a site that there is someone who likes more the sound of a yellow led instead of a red one. Why?
I hope that someone will reply to this post to understand this particular component.
Have a nice day.

[Seljer]

For a clipping diode, what you want to be looking at in the datasheet is the forward voltage and the current-voltage characteristic. That'll tell you the most about how it might actually sound.

Lower forward voltage means you'll need more less gain to get the same amount of clipping but you'll have lower output volume afterwards (eg: putting germanium diodes in a Rat of a Distortion+ circuit)

From the current-voltage characteristic graph you can see how gradually it will clip, will it be "soft" or very abrubt (if its very steep after passing the forward voltage on the horizontal axis). In the curve drawn you can ignore the upper portion of it as the typical current running through a clipping diode is only a couple of milliamperes.

Generally, diodes with a higher forward current rating will have a steeper characteristic, because the slope of the graph is effectively the equivalent resistance of the diode. And at higher current, higher resistances means more losses and lower efficiency so high power diodes tend to have very steep corners (for example a schottkey diode from a switching power supply).


LEDs are diodes just as much as any other diode. Different colours have different forward voltages.
The 1n914 and 1n4148 are practically the same 
In the end, you practically have to go by you ears to what sounds best (its fun to breadboard circuits before building them! )

[gjcamann]

The forward voltage drop tells you how much compression will occur in the circuit, so a lower Vf - like a Germanium Diode will cut off the voltage - or not allow the wave to get as big. Compared to something with a higher Vf - like a Silicone diode or LED's. More compression means less dynamics. That's the most measureable part of a diode.

The other thing that happens with a diode, is the shape of the "knee", and there's really no good way to measure this. If you took a sine wave and run it through a diode clipper pair, the tops and bottoms will get cut off, and the look of the curve in how it get's cut off is the knee. This is where the harmonics get added, and there's no formula, you need to determine how much compression you want in your circuit, then find diodes with similar Vf's and try them out and pick the one that gives you the best harmonics.

After clipping, instead of a sine wave, you have some funky looking wave with flat tops and bottoms. And in theory, you could take a bunch of sine waves of certain frequencies and amplitudes, add them together and get a wave that looks like this flattened sine wave. This "bunch" of sine waves are the harmonics that were produced by that particular diode.

[GibsonGM]

Well said, Seljer.  

In the end, you must only be aware of the forward voltage of the diode, and then experiment with different ones!  Unless a design calls for a specific diode, you can try different ones...and for clipping diodes, you can ALWAYS try others, although you may not retain the original sound of the device.   You will not hurt anything.

LEDs (varying Vf) are often said to sound 'gritty',  1N34's  (Vf about .3V) are said to be 'smooth' and 1N4148 (1N914), Vf about .5V, are sort of the 'middle ground', or the most common case.   I like LEDs because they have a wider range of Vf, and experimenting has more of a noticeable effect.  Where they turn on does have an effect on the sound, which is why I say to look at the forward voltage, mostly.    

You can also put different types in series to create asymmetrical clipping, which many like due to the different harmonics it generates.  Experiment!

[Seljer]

Also, some diodes have a notable amount of capacitance.

For example the 1N914/1N4148 are very fast (I've used them in radio circuits at many megahertz!) but LEDs and diodes made for 50/60hz (power diodes like the 1N4001) tend to have quite a lot, enough to be audible in the treble response of the circuit.

[GibsonGM]

Good point, Seljer.  Some higher frequencies may be attenuated by the diode capacitance.

[Rebel_88]

Thank you very much! so at the end I have to experiment and choose the diode I like more when I'm playing.
If I want more clipping effect I have to look at the forward voltage and the lower the forward voltage the sooner the signal clips.
And if i want bright sound I have to avoid slow (big capacitance) diode.

[GibsonGM]

You are close, Rebel.....I would simply try them all! As many as you can, mix them, use 2 in one direction, 1 in the other (or 3!).   Don't be afraid of the capacitance, let your ears decide!!!!   It may smooth things in a way you like!

More diodes = louder output, later clip....try different gains of opamp circuits....there are many, many ways to combine these things!

I would build a simple Distortion +, and try tons of diodes/combinations, to get started....