Clipping with LEDS

[bulldogguitars]

Has anybody made a comparison of the colors of leds when it comes to clipping in overdrive pedals. I was curious as to what you found tonally with the different colors. Im in the process of modding a DS-1 and was going to changed the clipping diodes to leds. And work on the tone control, that thing is terrible in my opinion. Thanks Danny

[Mark Hammer]

Delaware Ohio? Confusing for a Canadian, I have to admit. Isn't there a Miami Ohio also? Oh well, not any more confusing than London Ontario, I imagine.

All LEDs will clip because they are diodes, after all, and will behave as such. The question is whether they will clip at a signal level that is feasible. The LED colour with the lowest clipping threshold (around 1.5v) is red, and is approximately equal to using three 1N914 diodes in series for each direction. Other colours, because of the different composition, have higher thresholds.

Keep in mind that there is only so much amplification you can achieve with a 9v power supply, and the higher the clipping threshold, the lower the likelihood that you will be able to meet it. Also keep in mind that the guitar signal is generally well below peak levels most of the time, only rising to those juicy 100-200mv peaks when the pick initially hits the strings. What we will hear as distortion requires the guitar signal level to be at or above clipping threshold a greater percentage of the time. Fortunately, it is a normal requirement of diode-based distortion pedals to include some boosting, which brings the signal up to that point a greater percentage of the time.

When the clipping threshold is raised by whatever means (using an LED, using a different colour LED, using more diodes, etc), that now increases the likelihood that the guitar signal will start to be below the clipping threshold more of the time, resulting in less audible distortion.

The upside of changing to LEDs, and to non-red LEDs is that the ceiling on your pedal's output level will be lifted. If your amp is capable of producing pleasing distortion, then the pedal will be capable of driving that amp harder with the introduction of clipping LEDs that have a higher threshold. Just don't confuse what the pedal does on its own, regardless of amp, with what the pedal/amp combination will do.

All in all, red is the best current colour for LED-based clipping. Conceivably there will be other light-emitting materials in the future that will produce other colours and have different forward voltages than what can currently be found on the sales racks. For the moment, though, you will be best off using red.

BTW, the clipping action of the diode is separate from whether that LED with that sensitivity (in terms of millicandles per milliamp current) actually glows in a visible way. LEDs come in a wide range of brightnesses. So-called "garden variety" LEDs mave have a brightness rated at 60mcd (milli-candles), and those in the "superbright" category can range up to 6500 or more millicandles with the same current pushing them, even though they are the same colour, come in the same package format, and so on. The two types will clip the same, but the second type will visibly glow a bit when you strum harder, where the first type may generate enough photons to register on a supersensitive light-meter, but well below what your eye could detect.

[bulldogguitars]

Thanks Mark I appreciate your response. Its exactly what I was looking for. BTW there is a Miami, Ohio to, lol. I thought what I might do was socket the diodes and leds so I didnt burn up the board and give that a try for comparison sake. I didnt know having an led in there was like having 3 diodes in series. Now I also need to make some changes to the tone control on that DS-1 to make it usable. Thanks again Danny

[Enzo]

There is also Toledo, Ohio. Our friends in Spain will get that reference.

[Mark Hammer]

Thanks Mark I appreciate your response. Its exactly what I was looking for. BTW there is a Miami, Ohio to, lol. I thought what I might do was socket the diodes and leds so I didnt burn up the board and give that a try for comparison sake. I didnt know having an led in there was like having 3 diodes in series. Now I also need to make some changes to the tone control on that DS-1 to make it usable. Thanks again Danny

The analogy I find helpful is that of a doorframe. Clipping is analogous to people banging their heads on a low-lying doorframe. Typically, the initial attack of a picked note is akin to someone being 6'8", while the rest of the note is a mere 5'7". If you make everyone wear platform boots (a la Gene Simmons), then most people will bang their heads on the doorframe, not just the tall folks at the start of the note. If you raise the doorframe enough, no one will band their head. Of course, if you give everyone tall enough boots, they go back to banging their heads.

The threshold dictated by the type and number of diodes is the height of the doorframe. The height of the platform boots is the amount of gain applied before hitting the diodes, times the amplitude of the original input signal.

Germanium diodes (1N34, 1N60, 1N270, etc) have a forward voltage of around 200-250mv per diode. Silicon diodes (1N914, 1N4148, etc) have a forward voltage of around 500-600mv per diode. Red LEDs have a forward voltage of around 1500mv. Stick a Ge and Si diode in series and you have a combined forward voltage of around 700-800mv. And so on