# Clipping Mod Experimentation



## Stratin2traynor (Sep 27, 2006)

Just finished "designing" a clipping mod for my BYOC 250+. It's going to have a 6 way rotary switch with different clipping choices: Bypass, 4001, 914 asym, LED, Germanium, Mosfet. The Mosfet clipping sounds awesome - very OCD ish. I've also added a tone knob for extra tweakability. I have an enclosure for it but I still have to figure out how to fit everything in there. 

I'm really happy with the results. Each clipping section has it's own flavour. 

Anyone else experimented with their pedals??

Any other clipping suggestions???


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## exhausted (Feb 10, 2006)

i like assymetrical arrangements usually.

i had a rat clone with a 914/germanium pair that sounded nice. my big muff clone has J201 fets instead of silicon diodes in the second stage. i have a marshall bluesbreaker clone with 3 Si diodes and an LED that i really like too. 

the rest of my homebuilt overdrives are JFET based so no diodes at all.


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## Emohawk (Feb 3, 2006)

I built a BYOC Screamer with a 4-way rotary for clipping mode. Stock, 914 asym (2/1), germanium asym (3/1) & LED asym (3/1).


The germanium mode is the smoothest (but with a big volume drop...always the case with those diodes) with the LED mode being the most Marshall-ish.


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## Stratin2traynor (Sep 27, 2006)

Well, I finished the pedal last night. Completely assembled in a nice shiney red enclosure with a bright violet LED. Looks great but there are only 3 of the six positions that sound good: LED, Mosfet, and Silicon Diodes (with massive volume drop). The other positions all sound the same. I likely made some kind of mistake when doing the final build because when I initially tested it, all the positions sounded different and had their own flavour. Gonna have to take it apart now and figure out where I went wrong. 

ARRRGGGHHH!!!


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## mhammer (Nov 30, 2007)

People make far too much of clipping diodes if you ask me. It's a bit like the craze we used to have in the 70's for all those phase-switching options. At a certain point, once the amp is turned up, differences between them are inaudible. That's not to say that differences in clipping diodes and combinations make NO difference. Rather, there are differences you can hear all the time, and differences you can only hear when things are set up just so. Personally I prefer to build those things into a pedal that I can hear all the time, or any time I want, and ignore those options that require some precise alignments of the planets and amp controls to be heard.

The other thing many forget is that changing diode type changes the clipping quality by changing the clipping threshold. No doubt, you will have noticed a big difference in output volume depending on diode type. That's because the lowering or raising of clipping point is accompanied by lowering or raising of maximum output signal amplitude.

Note as well that in the stock DOD250 and Distortion+ designs, as the gain goes up the bass gets chopped. At max gain, when all you have is the .047uf cap and 4k7 resistance (pot = 0 ohms at that point), there is a bass rolloff starting around 720hz. There is a good side and bad side to that. The good side is that as you increase gain, you also apply gain to any hum entering along with the signal. If signal components in the range of hum do not receive as much gain as the musical parts of the signal, then you don't pay the price of having this godawful hum with max distortion sounds. The other semi-positive aspect is that if you trim bass from the signal as you turn up gain, the more distorted settings will have more "bite", which is what people bought the unit for in the first place.

The down side is that chopping content below 720hz pretty much guts the signal and can make it sound wimpy. As well, since most of the signal lives down in that zone anyways, you aren't pushing the diodes as hard as you might when you turn the gain up. That will be particularly true when using higher clipping threshold diodes like LEDs or pairs of silicon diodes.

Consequently, if you can abandon any reticence about amplifying hum (remember that in the 70's, when the 250 appeared on the scene, single coil *meant* single coil, with all the hum that entailed), increase the .047uf cap to .1uf, .22uf, or even .47uf to allow for more gain applied to the bass end. That will bring the balls back to your signal and also allow for more clipping potential even with LEDs. You can always wire up a second cap in parallel with the stock .047uf unit and use a toggle to switch it in circuit


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## Teleplucker (Feb 5, 2006)

Is there any way to generalize how, under similar or identical conditions, each type of diode sounds (or changes the sound)? For example, does one let more low end through than others? Is one more compressed then others? Does one give more of a volume boost than others?

I did some experimentation with an SD-1 by socketing one of the diode spots. I'd have to find my notes, but it seemed like the LED was fatter and less compressed with more volume boost than the silicon diode. 

I'm hoping someone will be able to generalize so that i can start to experiment with changing the other clipping diodes in that pedal. It still lacks "openness" (I know that's a horrible description, but it fits what I'm hearing and feeling) in sound and touch sensitivity. I've heard that changing the cheap caps will help this, but I'd also imagine that the clipping diodes would have an effect.

Anyone? Mark?


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## Stratin2traynor (Sep 27, 2006)

You should try a Mosfet clipping set-up. You can find the directions on the BYOC Forum. It is a notation under Rat OD mods. I would post the link but my internet connection is acting up and not letting visit certain web pages. Luckily I can still get to GC!!

It's pretty easy to do - even I was able to do it!! It's a hair quieter than to LED clipping but sounds fuller. Probably what you are looking for.


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## mhammer (Nov 30, 2007)

Teleplucker said:


> Is there any way to generalize how, under similar or identical conditions, each type of diode sounds (or changes the sound)? For example, does one let more low end through than others? Is one more compressed then others? Does one give more of a volume boost than others?
> 
> I did some experimentation with an SD-1 by socketing one of the diode spots. I'd have to find my notes, but it seemed like the LED was fatter and less compressed with more volume boost than the silicon diode.
> 
> ...


Diodes are categorizable in terms of what is called forward voltage, AKA voltage drop. That is the voltage at which they conduct. If the forward voltage is higher, then that provides, in theory more dyamic headroom. In other words, the contrast between softer and louder picking will be audible, and the net tone will seem less "compressed". The reason why people switch to red LEDs is generally because the red ones have a forward voltage some 3x that of a standard silicon diode. This gives more headroom. Given that most of the signal lives in the low end where the fundamental is, and that a low clipping threshold tends to compress the lower notes moreso than the higher (lower amplitude) ones, small wonder that the sound is "fatter" to you.

If the forward voltage is higher, that also means that it takes a significantly higher amplitude signal to reach the clipping threshold, and that means in turn that the output can be significantly louder too. If I take my homebrew Distortion+ (where the max volume is set by the diodes, and only subtracted from by the volume control), switching from germanium to silicon diodes results in double the output level, and were I to install LEDs it would go up from there too.

Though one can use other colours than red, red LEDs have the most practical forward voltage of the various-colured LEDs, with yellow and green being higher because of the different materials used. The brightness of the LED has essentially no bearing on the tone. LEDs are rated in terms of luminance (in millicandles or mcd), with older variety ones being as low as 50-100mcd and the newer more efficient ones giving off as much as 6000mcd with the same current. If you use a high-brightness LED, then you may see some visible flicker when you strum, but whether you do or don't see any, the forward voltage will be the same for dark and bright.

Forward voltage is additive, meaning that if you had an LED with a forward voltage of 1.5v (a typical value), and 3 silicon diodes in series with each having a forward voltage of 500mv (also a realistic value for that type of diode), the LED and string of Si units would have the same voltage drop (forward voltage), including the clipping threshold they introduce and headroom effect. Would they have the "same" quality of distortion as each other? It would depend. Some folks who have put this to the test in clinical conditions say yes, though I myself have never knowingly heard it. Given that the two diode types "turn on" at different rates, it stands to reason they *can* sound different. Remember that the clipping you hear results from the diode conducting, and if diode A starts to conduct more slowly that diode B, especially given that most of the high end "lives" at the start of the note when you pick, then it stands to reason that the different diode types will exert qualitatively different impacts on the different parts of the spectrum, based on their conduction speed.

Having said that, far too many folks tend to confuse the effect of having a very different clipping threshold resulting from use of this type of diode vs that one, with the qualitative aspects of the clipping produced. In theory, ANY diode can be made to clip the exact same amount, assuming the power supply and gain structure permit. To use an analogy, I can make the tiniest dwarf bang their head against the ceiling repeatedly if I put them on stilts tall enough. It just happens to be the case that most rooms and doorframes are designed around the assumption that few people will be above 6'8". Similarly, the amount of gain applied to the signal in a 9v-powered distortion assumes an input signal of a given amplitude. This is, of course, why you can make any distortion sound more savage simply by providing boost to the signal in some manner before you feed it to the distortion.

You really DO owe it to yourself to read some of the warping articles at AMZ for a wealth of info about creative clipping options.


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