RobertJay wrote:
Here's what I noticed. In the diode section, the instructions say to solder the lead on the end that has the line. The cathode, negative, identified with a line, into the square pad. With that, I installed the 3 mm LED's for the clipping Marshall Stack Mod in the same fashion. I soldered the short lead, the cathode, negative to the square pad. But later in the build, the instructions want us to solder the LONG leg of the 5 mm LED to the square pad. The long leg being the positive Anode, NO? Am I overthinking it? Should I be following the instructions more than thinking about what little I may know about the anode and cathodes?
Yeah, I would suggest that you just follow the instructions and not worry about the cathode/anode question. The instructions get vetted very early after first release, so if there are errors that interfere with the pedal's proper operation, they get sorted out quickly.
What is important for clipping diode pairs is that they get installed in
opposite directions of polarity. This is because the audio signal is "AC", i.e. it's a wave form with positive and negative nodes about a zero voltage center line. Since diodes only pass signal in one direction, one diode will clip the positive signal (assuming that it exceeds the diode's forward voltage threshold) and the other oppositely-oriented diode clips the negative signal.
RobertJay wrote:
As far as these clipping Mods go, is there no description of what to do to achieve what sounds? Is all of this trial and error? How can one anticipate what a mod will do? For more crunch, do this, for more attack, do this.....
Different types of diodes have different forward voltage thresholds, which changes the amount of signal that they clip and the amount of distortion and compression that they create. For example, germanium diodes have a very low voltage threshold, about 0.25V, so they will bleed off the signal that exceeds that value. This results in a lot of distortion and compression, and the output volume is considerably reduced. LED's, on the other hand, only clip above 2 - 3V, depending on the LED type, so they result in a much louder and less distorted/compressed output, though it takes a considerably stronger input signal to get them to clip. Silicon diodes are in between, at about 0.6V threshold, so their clipping characteristics are in between, as well. If you want a very fuzzy, compressed sound to your overdrive or distortion, germanium diodes are a good choice....if you can tolerate the volume loss. LED's will give you a much louder and more open sound, often described as "crunchy" or "Marshall-like." Silicon diodes are probably the most commonly used for clipping, and give you a tonal character in between these two. There are some additional subtleties in how these diodes work & sound, but I won't get into that here. There's plenty more info on the internet, if you're interested.
RobertJay wrote:
I did read the clipping mod section and am interested in the Marshall Stack sound. Being told to use the 3mm LED's. I will take that to mean LED only. I'll jump the other spots. I'll use 1 LED and 1 jumper per series section. But is that what the instructions say?... Or 2 LED's in the same group and jump the other set? All options should still work as some form of a Mod, but I want the intended sound as instructed.
Yes, one LED in each of the blue and green highlighted diode spots, with a jumper in the other position of the pair.
You can also get into asymmetric diode arrays, where you have different types or numbers of diodes on each side, or stacking multiple diodes together in series on each side; diodes in series have thresholds that are the sum of their individual thresholds. Again, the internet is full of more info on this subject.
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