Diodes

 

What are diodes?

There's not much that you need to know about diodes.  They are simple devices, often quite small, with two leads.  Their primary function is allowing current to flow through them in one direction, while blocking current in the other direction.  Some of their main properties include how much current and voltage they can handle, what voltage levels they allow through, and how much current leaks through them in the direction they are blocking. 

What are diodes used for?

There are many, many models of diodes, and diodes are used in effects circuits for multiple purposes.  Most of those purposes are of a technical nature, and while important, they aren't useful to discuss.  Those uses often require diodes with specific properties and there's little or no room for choices, and often little or no impact on the tone of the effect.  There is one major exception - clipping.  You can see more information about clipping at Clipping Configurations. 

What influences clipping tone?

If you are reading this, then you probably know that there are many opinions about which diodes sound good, which ones have special "mojo", and which super-secret-unobtainable diodes were used in a specific pedal.  Multiply that by many dozens of pedals and many dozens of diodes and many opinions and you have a big mess to sort through.  We'll certainly agree that it is messy.  Let's try to simplify a little so we can focus first on the facts, then put the "mess" in perspective.

Types of clipping diodes

 

 

 

 

The first fact is that there are three primary categories of clipping diodes: germanium, silicon, and LED.  There are many kinds of germanium and silicon diodes, but only a few types of LEDs, even fewer that are probably useful.  As general guidelines, based only on diode type, it is reasonable to say that:

• germanium diodes result in smoother clipping, tending toward warm to dark tones
• germanium diodes clip differently at different temperatures
• silicon diodes result in more aggressive clipping, tending to be brighter than germanium
• LEDs seem "crunchy"
• silicon diodes and LEDs are not much influenced by temperature

The type of the diode is the biggest indicator of how the clipping will influence the sound of the effect.

Diode Forward Voltage, Vf

The next fact is somewhat more technical.  Diodes have a property called "forward voltage" or Vf.  That is the voltage at which they clip.  Any signal above that voltage gets chopped off.  The amount of clipping depends on the Vf, but it also depends on the voltage of the signal.  If the signal doesn't contain voltages that would be clipped by a particular diode, then the impact of the diode on the tone becomes minimal and the signal passes cleanly, or nearly so.  If the signal voltage is high versus the diode's clipping voltage, then lots of signal gets clipped and you get heavy distortion.  Also, the more you clip, the lower your volume may go.  Some circuits make up for that volume loss, others do not.

It's unlikely you will know anything about the voltages inside an effect circuit, so this is one of the contributing factors to the "messiness" of selecting clipping diodes.  It's not often that a player measures the voltages inside his pedals while he's ripping off an epic solo.  Even though those voltages will almost certainly land within a small range, that small range is much larger than the range of Vf values provided by clipping diodes.  Instead of trying to do some fancy measuring and calculating, it is generally good to go with experience instead.  It's much more reasonable to discuss what type of diode sounds good in a particular effect circuit.  Then you can look up the Vf for those diodes that sound good and see how that compares to the Vf of other diodes.  Then you can choose diodes that are the same, comparable, or very different, depending on your goals.  Since we've already provided a few generalizations, we may as well pile on a few more:

• Germanium diodes are often thought of as clipping at pretty low values, generally around 0.3 - 0.4V.  However, just like germanium transistors, they have very wide spec ranges and also have a very wide range of actual values for Vf.  While many do have a Vf in that range, others may be as low as 0.20 - 0.25, or as high as 0.4 - 0.85.  All those values are within the common spec range of "no more than 1V". 
• Silicon diodes mostly all have a Vf of around 0.6 - 0.7V.  They do vary a bit outside that range, but usually not that much, maybe 0.55 - 0.75.  Vf isn't normally the major distinguishing characteristic between different silicon diodes.
• LEDs clip at higher voltages, from nearly 2V to around 3V.

Think of Vf as primarily determining the amount of distortion you will get.

Diode brand and model

After type and Vf, the last thing we'll address here that can affect the tone produced by clipping diodes is the brand/manufacturer and model number.  You won't see many specs for diodes that indicate much about their impact on an audio circuit.  But they do vary in sound between manufacturers and model numbers.  Again, this is where experience or experimentation are needed to make more detailed selections of models and manufacturers.

The final fact we'll conclude with is also responsible for a lot of the "messiness".  There are generally lots of other things going on in a circuit besides clipping.  Every circuit manipulates the frequencies and voltages in the signal.  This filtering can easily swamp the effect on frequencies caused by the clipping diodes.  Clipping diodes of a particular brand and model may well impact the frequencies in your signal, but they aren't likely to affect it as much as the circuit's filtering.  If you try two different silicon diodes in the same circuit, the differences in tone will likely be pretty subtle.  You'll have to listen carefully to hear it most of the time, if you can hear it at all.

Germanium Diodes

Germanium diodes are getting pricey, and there are lots of fakes out there.  Even with reputable dealers, it is sometimes difficult to know what you are getting since many are unmarked, or have markings that do not identify either the brand or model.  Fakes are generally easy to sort out.  Genuine ones that are unmarked are virtually impossible to identify with certainty.  None of these are available from original manufacturers, so they have changed hands and could be misidentified.  Models are probably correct, but brands are often completely unknown or cannot be verified.  Others we know only what our suppliers told us.  We have no reason to believe any of our info is wrong, but we cannot independently verify all of it.  For those reasons, we can't absolutely guarantee brands or models of germanium diodes.  We know the type (germanium vs silicon vs LED), we can measure Vf, and we can audition them in circuits. That's really all we need.

 

 

There are some new production diodes being sold as germanium diodes.  We refer to them as "the little orange fakes".  They are probably Schottky diodes.  The manufacturer uses the same part numbers as the popular old germanium diodes, such as 1N34A and 1N270.  They have some properties of the old diodes, but they are different.  Some effects builders use these diodes.  They are completely functional diodes and sound OK, but it seems a little misleading to use the old part names for something entirely different, regardless of the sound.  NOS germanium diodes of good quality cost much more than these new diodes.  We have some different models of these new diodes, and they do sound OK, so maybe we'll use them from time to time - we presently don't.  We do offer them as options, since there's a good chance you have them in some of your pedals already and may want to try them in our modules if you like them.

Silicon Diodes

Most current diodes (other than LEDs) are silicon.  Most current silicon diodes are widely available, usually at very low cost.  However, there are some vintage silicon diodes that are not generally available and are expensive.  Since basic silicon diodes tend to sound identical or nearly so, it is rarely worth the extra expense or worry about trying to use "vintage, circuit-correct" clipping diodes.  It's certainly OK to do so if it gives you some peace of mind, but your ears probably won't hear a difference between them and modern inexpensive replacements.  In spite of any hype you may read about super-secret, custom-made, unobtainable diodes being key to the sound of a particular effect, good builders can build that same effect with completely different diodes and you won't be able to hear a difference, or at least any difference you hear won't likely be due to the clipping diodes.

LEDs

LEDs are widely available and inexpensive.  For clipping, it is rare to use anything other than red LEDs.  The Vf for other colors may be too high for some circuits. They sound great in many overdrive and distortion effects and are often a good candidate for use in an optional clipping config in our modules.

Picking your clipping diodes 

It's not rocket science.  Consider the clipping configuration and diode choices of the original circuit, as well as how much distortion and volume the clipping gives that circuit.  Do you want more or less distortion and volume?  Pick your clipping configuration(s) and Vf values for that configuration to give you more/less distortion, less/more volume - lower/higher Vf.  Decide on the general character of distortion you want to help guide diode type selection - germanium, silicon, or LED.  Then check around to see which specific diodes others may have tried in that effect and how it turned out.  Pick your specific diodes.  Clipping diodes can provide significantly different tones, so selecting multiple switchable clipping configurations for modules that support it may provide you with more tones and more bang for your buck.  However, you may also get considerably different volume levels when you switch diode configurations.

Don't worry - we don't abandon you during this process if you need some help!  We can't tell you what you want your tone to be, but we can help you select diodes for more/less distortion, help with volume levels, and the more technical/factual aspects of configuring clipping options.  We won't always know "the answer", but that's still OK.  When we build modules with custom clipping options, we will put sockets on the boards so that we can audition the diodes.  If we hear something that seems "off", we'll let you know at that point before we solder them in.  For example, if your configuration choices sound almost identical, then we would let you know in case you want two tones that are more different.  Or if you want a smooth clipping sound and we end up with something aggressive.  If something goes significantly off the rails, this gives us a good chance of catching it before it is finalized in the build.  Of course, even then there is usually the option of removing them and trying something else later.

Clipping Diodes for GT Rack Effects

Below are some clipping diode types we have in stock at the time of writing.  We are always searching out, and sometimes running out of, good diodes, so this list may get out of synch with our inventory.  Since germanium diodes have varying Vf values, we may have different ranges of them available for some models.  We don't list the brands, since we get different brands as they are available, or we don't know the brands.  We've not yet known the brand of a particular model of diode to have any significant impact on tone - it could, but we just haven't methodically tested for it.  You can find spec sheets for all of these online if you want to take a look at them, though that shouldn't be necessary.

Germanium Diodes

• 1N100A
• 1N270
• 1N270 "orange fakes"
• 1N276
• 1N34A
• 1N34A "orange fakes"
• 1N60
• 1N60 "orange fakes"
• 1N949
• 1S188FM
• 2AA113
• AA113
• AA143
• D18
• D2D
• D2B/D2V
• D311
• D9B
• D9E
• D9J
• D9K
• D9V
• DR271
• OA7
• OA90
• OA91/CV7130
• OA95
• OA126
• OA1150
• OA1160

LED

• orange
• red
• yellow
• green
• pink
• blue
• white
• violet

Silicon

• 1N4001
• 1N4002
• 1N4004
• 1N4005
• 1N4007
• 1N4148
• 1N4150
• 1N5225B
• 1N5242B
• 1N5399
• 1N5408
• 1N5817
• 1N5818
• 1N5819
• 1N5822
• 1N6263
• 1N914
• 1N916
• 1S1588
• 1S2471
• 1S2473
• BA100
• BAT41
• BAT42
• BAT46
• BAT85
• FR107
• FR207
• KD510A
• KD521A
• KD521B
• KD521V
• KD522B
• MA150
• MA856