# Using LED's Instead of Diodes



## mrfiftyfour

Good Evenin' Gents,
I've been browsing some DIY pedal sites and I've read about swapping out diodes and using LED's instead. 
Anyone try this and how were the results?
I went down to The Source and the only LED's I found were little lights!
These can't be the same thing can they?


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## keto

I'm just sorta getting into the DIY hobby myself, and haven't done what you describe yet. I do know different grades and sizes and colours of LED's have different amounts of gain....and even the same 2 LED's can be matched/mismatched, though I don't yet know how that's determined. GENERALIZING I'm pretty sure LED's impart more gain than a diode, and there may be other tuning required depending what circuit you're looking to put them in.

Someone who actually knows what they're talking about will likely be along shortly


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## jcayer

mrfiftyfour said:


> ...I went down to The Source and the only LED's I found were little lights!
> These can't be the same thing can they?


LED = Light emitting diode 

Typical diode voltage drop (silicon) is around 0.65V. Voltage drop for led is anywhere from 1.4V to well over 3V depending on the LED type. Be careful, there are diodes that can't be swapped because of their purpose in the circuit.


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## sambonee

There's a guy in the Beaches area of Toronto who had a great video on youtube showing his moded mxr dist.+ with an added LED light for the gain stage. It actually became 2 pedals in one. I sounded awesome. It later went up for sale on Clist here in Toronto and I missed it. 

We actually chatted and he said on the phone that he'd do the mod for $60! 

He was playing a champ 








keto said:


> I'm just sorta getting into the DIY hobby myself, and haven't done what you describe yet. I do know different grades and sizes and colours of LED's have different amounts of gain....and even the same 2 LED's can be matched/mismatched, though I don't yet know how that's determined. GENERALIZING I'm pretty sure LED's impart more gain than a diode, and there may be other tuning required depending what circuit you're looking to put them in.
> 
> Someone who actually knows what they're talking about will likely be along shortly


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## Wild Bill

mrfiftyfour said:


> Good Evenin' Gents,
> I've been browsing some DIY pedal sites and I've read about swapping out diodes and using LED's instead.
> Anyone try this and how were the results?
> I went down to The Source and the only LED's I found were little lights!
> These can't be the same thing can they?


Yep! The only difference between a regular diode and a Light Emitting Diode is that the LED emits light!

Plus, the LED has a completely different voltage drop, of course!

In a clipping circuit using regular diodes, wiring a pair back to back will clip off any portion of the wave greater than the diode's voltage drop, typically 1.2 volts with a 1N4007. LED's usually have a Vd of maybe twice that. So they will clip at a higher level, meaning the signal stays cleaner longer.

Diodes have no gain at all. They are completely passive devices. They rectify AC and they will clip a signal but they will not make it any louder by themselves.

This changes your sound. It's up to you if you like it better.


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## Guest

Diodes (which LEDs are) don't add gain. Gain is what you use to describe the effect of creating a louder output signal than input signal.

In your typical OD pedal diodes are used to clip the signal. Literally they shear off the peaks of the wave. They *distort* the wave. Where this clipping starts depends on the forward voltage rating of the part. Diodes can be had with a range of forward voltages, giving you ways to experiment with different amounts of clipping, different amounts of distortion. You mix transistor-based gain stages to boost and clip (or clip then boost depending on the design) until you get the distortion you seek. Clipping and boosting multiple timed to really get crazy distortion (think Big Muff here) or just doing it once to get a little bit of distortion (think D+ here).

Edit: Bill best me to it.


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## keeperofthegood

_EDIT: Just realised, the waveforms I didnt lable. If you take the four circuits as:
A B
C D

Then the waveforms out across the bottom are A B C D

_
Here are some simulations that I hope will shed some light on the LED vs Silicon vs Germanium vs Zener (and there is no version of yet of other types such as Schottky diodes which have 0.2v forward drop or less)

You can see that the clipping action is sharper with the plain diode than the Zener diodes. I tried a series of Zener voltages and the wave form stayed that way at that voltage level. You can see the crossover distortion in the clamper circuit using the silicon diode and using the Zener it acted more like a simple resistance.










Concentrating on JUST the diode clippers, here are 4 different voltages, representative of:
Germanium, general purpose Silicon Diode, general purpose LED, and White LED

You can even use a microwave oven diode but I think you can see that no matter how large a voltage drop across the diode you have, the clipping action is rapidly lost when the value of the drop is greater than the value of the signal in. 










People will talk about using mixed diodes, multiples etc, and achieving a different sound. Here, I simply slid off one diode, and you can see how the Positive going wave is distinctly different than the Negative going wave:










And finally, I upped the voltage here to 10 volts in. Here you can see that the diodes DO still clip. Even though before they appeared to have lost their ability to clip, it is a matter of Signal Level In VS Diode Voltage Drop, and with larger signal levels, using more diodes or higher voltage dropping diodes will have a broader range of effect than when dealing with low levels of signal in.










If you want to futz with this yourself, use this link, it will pop a window that is the simulator:

http://www.falstad.com/circuit/

Click on:
FILE
IMPORT

and paste the following in:

$ 4 4.9999999999999996E-6 0.0 50 5.0 50
R 224 128 224 80 0 1 100.0 10.0 0.0 0.0 0.5
r 528 128 528 272 0 100000.0
d 368 128 368 272 1 0.205904783
d 320 272 320 128 1 0.205904783
w 320 128 368 128 0
w 368 128 528 128 0
g 320 272 320 304 0
g 368 272 368 304 0
g 528 272 528 304 0
g 992 272 992 304 0
g 832 272 832 304 0
g 784 272 784 304 0
w 832 128 992 128 0
w 784 128 832 128 0
r 992 128 992 272 0 100000.0
R 688 128 688 80 0 1 100.0 10.0 0.0 0.0 0.5
r 784 128 688 128 0 100.0
r 224 128 320 128 0 100.0
r 224 384 320 384 0 100.0
r 784 384 688 384 0 100.0
R 688 384 688 336 0 1 100.0 10.0 0.0 0.0 0.5
r 992 384 992 528 0 100000.0
w 784 384 832 384 0
w 832 384 992 384 0
g 784 528 784 560 0
g 832 528 832 560 0
g 992 528 992 560 0
g 528 528 528 560 0
g 368 528 368 560 0
g 320 528 320 560 0
w 368 384 528 384 0
w 320 384 368 384 0
d 320 528 320 384 1 1.805904783
d 368 384 368 528 1 1.805904783
r 528 384 528 528 0 100000.0
R 224 384 224 336 0 1 100.0 10.0 0.0 0.0 0.5
d 784 528 784 384 1 2.805904783
d 784 272 784 128 1 0.805904783
d 832 384 832 528 1 2.805904783
d 832 128 832 272 1 0.805904783
x 156 194 303 200 0 24 Forward Drop
x 158 231 302 237 0 24 205.904783m
x 613 476 750 482 0 24 2.805904783
x 611 439 758 445 0 24 Forward Drop
x 617 227 761 233 0 24 805.904783m
x 615 190 762 196 0 24 Forward Drop
x 153 475 290 481 0 24 1.805904783
x 151 438 298 444 0 24 Forward Drop
o 1 64 0 291 0.2734063405978765 2.6699837949011377E-6 0 -1
o 14 64 0 291 1.093625362391506 1.0679935179604551E-5 1 -1
o 34 64 0 291 2.187250724783012 2.1359870359209102E-5 2 -1
o 21 64 0 291 4.091738259870177 3.9958381444044705E-5 3 -1


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## mhammer

1) All diodes have a "forward voltage". That is a voltage above which they will conduct. When they conduct they behave like a low-resistance path to the signal. The threshold at which they will clip is a function of the forward voltage. Depending on the material the diode is made from, the forward voltage will be different. Germanium diodes tend to have a forward voltage between 190mv and 300mv. Silicon diodes tend to have forward voltages ranging from 500mv or so up to around 650mv. LEDs are frequently made from gallium-arsenide and have forward voltages in the 1500mv+ range. Within LEDs, different colours have different forward voltages. Red has the lowest at 1500mv, and green, yellow, etc., have higher. Generally speaking, only red are used in stompboxes, simply because higher forward voltages introduce requirements that are not easy to meet when powering something with 9v. Some diodes (Schottky) have such a low forward voltage that they can actually introduce clipping without having to boost the normal output of a guitar's signal. Those diodes are found in those little passive clipper add-ons called "Black Ice".

2) LEDs vary in terms of how much visible light they will produce in response to input current. They will be rated in terms of the number of "millicandles" of luminance they produce. Standard ones are usually in the <300mcd range. Others are described as "superbight" and can produce in excess of 3000-5000mcd before they burn up from too much current. The result is that, even though they function identically _as diodes_, some will light up under normal signal conditions, and some don't. Whether they do or don't is NOT an indication of whether they are working properly or not, in the context of clipping. It is completely possible for a fully-functioning red LED to do its clipping and not emit anything visible.

3) While the transition from conducting to non-conducting state is slightly different across diode types, the major differences the average user will *hear* are 99% dependent on simply shifting the forward voltage and resulting clipping threshold. This will be a function of the total combined forward voltage of _all diodes pointing in the same direction for each direction_. So, a single red LED might pose a forward voltage of 1537mv (for that specific LED), a series of three silicon diodes (1N914, 1N4148, 1N4001, etc.) may pose a combined forward voltage of 1678mv, and a series of seven germanium diodes (1N34a, 1N60, 1N270, etc.) might pose a combined forward voltage of 1692mv. Two silicons (in series) going one way and 3 germaniums (in series) going the other way may get you an arrangement that conducts (exceeds the forward voltage) when the positive peaks exceed 725mv and the negative peaks exceed 1036mv. Long story short, the same forward voltage can be achieved many different ways, and diodes can be used in different combinations to achieve a variety of symmetrical and asymmetrical forward voltages and clipping thresholds. What people think they "need" LEDs for may simply be a matter of adding one more normal diode in series with what they already have.

4) The quality of clipping in guitar pedals *is never, and has never,* been a function of the diode type used. It is always, always, and forever a function of the signal level _*relative*_ to the diode arrangement used. If the signal does not reach the forward voltage of the diodes, then no clipping occurs. Many seeming differences between pedals that use different diode arrangements can often be attributed to how much gain they apply to the signal, dictating how likely the signal is to exceed the forward voltage. This means you can usually make any diode-based distortion sound "sicker" simply by feeding it a hotter signal, such as that from a booster or EQ. It also means that often the same sound quality can be achieved without changing diodes or diode type, merely by adjusting the internal gain of the pedal. A Tube Screamer uses a pair of 1N914 diodes, and so does a DS-1, but they don't sound anything alike. Part of that is because the DS-1 applies much more gain.

5) The quality of clipping that a diode produces is also largely a function of the peculiarities of the guitar signal. Guitars produce a big transient peak when picked, and then settle down to a less harmonically-rich sustaining tone that turns into mostly fundamental before dying out. The end result is that, while the clipping threshold might be fixed at a certain point, the guitar signal does not always occupy the same "distance" from that point. In general, the sonic quality of the clipping produced, from a musician's point of view, is dependent on what proportion of that note's lifespan is above the forward voltage. For the first 200msec or so, the guitar signal may spend 60% of the time above the forward voltage (especially if enough gain is applied), but after that, maybe only 20% of the time for the next 500msec, and only 5% for the 500msec after that. That will be heard as a nice "bite" with a bit of harshness introduced afterwards, but nothing you'd call "fuzz". Many of the mental/marketing categories we have for introducing distortion are really a function of how long the signal tends to remain above the clipping threshold. Longer = fuzz, shorter = overdrive.

6) Your total heard distortion (THD?) will always be a function of the *cumulative* clipping throughout your entire rig. So, the cleanest pickups in the world into the cleanest booster and cleanest amp can still extract tortured breakup from your speakers if they are pushed hard enough. I mention this because what you end up hearing is not just what the pedal does on its own, but what he pedal does to everything that comes after it. And I mention THAT because changing a pair of diodes to a pair of LEDs, without a change to the gain of the pedal or input signal amplitude (gain is gain, no matter where it comes from) will reduce the amount of clipping produced (raise the ceiling and the signal; stops bumping its head), BUT result in a higher output level from the pedal and THAT will push your amp harder, which will, in turn, yield its own clipping. In other words, changing from silicon (or germanium) diodes to LEDs will have the effect of shifting the burden of clipping from the pedal to the amp. If your amp produces nice clipping, great. If your amp clips ugly, then maybe LEDs is not such a great idea.

7) Because changing the diode type or number permits a higher or lower ceiling, you get corresponding output volume level changes. I have a germanium/silicon switch on my homebrew Distortion+, and every time I change the diode type, I have to fiddle with the volume control. That's not a huge problem for me since I don't gig, but it might be an issue of practicality for someone who does. There are ways to fix that so that you get essentially equivalent volume levels, but I'll leave that for another time.

8) I mentioned the constraints of using a 9v-battery-powered pedal earlier. Please note that as one raises the clipping threshold by changing diode type/number, that can often shift the burden not only from the pedal to the amp,but from the diode to the semiconductors used. Consider this. Agreat many distorting pedals use op-amp chips. A great many of those chips cannot "swing" any wider than the extremes of the power supply minus 1.5v in each direction. So, if you have a 9v supply, the chip can only produce voltage swings ranging from 1.5v at the lowest up to 7.5v at the highest. The midpoint is 4.5v, which means the chip is unable to produce a swing of more than 3v in either direction. In a sense, the chip itself has "headroom" limitations. Okay, now, let's consider something like the venerable Proco Rat pedal, and the venerable Strat pickup. Depending on how you pick it, a Strat pickup will produce around 60-80mv output from any single note on an unwound string. The Rat provides, at maximum setting, a gain of over 2000x. So let's do some math. How many times does +/-80mv go into +/-3v? Thirty-seven and a half times. Right away you can see that at higher gain settings, the signal/design is forcing the chip to do what it cannot do: swing wider than +/-3v. In other words, only _part_ of the resulting sound comes from the diodes. Another part of it comes from the strains placed upon the chip within the context of a 9v power source (whather battery or wallwart). Many folks who have built a Distortion+ clone have remarked that even without any clipping diodes, the thing never actually sounds clean. That's because the chip's weaknesses are exploited in that design, and the diodes simply add into the sonic mix. And, as noted earlier, ultimately, the tone you hear is a function of what the pedal does to the amp and what the amp does to the speaker. So, the diodes certainly play a role, but they are not absolutely pivotal in what it is you get to hear at the end.


If you let me know what you were thinking of installing the LEDs in, I could probably provide some guidance on what to expect, and whether it's a good idea or not. As with any sort of modification, context is very important.


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## jcayer

Great post Mark (as usual...)


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## Guest

mhammer said:


> Long story short, the same forward voltage can be achieved many different ways, and diodes can be used in different combinations to achieve a variety of symmetrical and asymmetrical forward voltages and clipping thresholds.


You mentioned the "asymmetrical" word.  To the OP, take a look at the nice diagrams that Keeper posted. You'll see in all the circuits that the diodes are paired. This is done so the clipping occurs evenly on the part of the signal that is above 0 V and the part that is below 0 V -- it's a symmetrical setup. You can use different clipping diodes in pairs giving you more clipping on one part of your wave form and less on the other. That'd be an asymmetrical setup.



> 8) I mentioned the constraints of using a 9v-battery-powered pedal earlier. Please note that as one raises the clipping threshold by changing diode type/number, that can often shift the burden not only from the pedal to the amp,but from the diode to the semiconductors used. Consider this. Agreat many distorting pedals use op-amp chips. A great many of those chips cannot "swing" any wider than the extremes of the power supply minus 1.5v in each direction. So, if you have a 9v supply, the chip can only produce voltage swings ranging from 1.5v at the lowest up to 7.5v at the highest. The midpoint is 4.5v, which means the chip is unable to produce a swing of more thaqn 3v in either direction. Okay, now, let's consider something like the venerable Proco Rat pedal, and the venerable Strat pickup. Depending on how you pick it, a Strat pickup will produce around 60-80mv output from any single note on an unwound string. The Rat provides, at maximum setting, a gain of over 2000x. So let's do some math. How many times does +/-80mv go into +/-3v? Thirty-seven and a half times. Right away you can see that at higher gain settings, the signal/design is forcing the chip to do what it cannot do. In other words, only part of the resulting sound comes from the diodes. Another part of it comes from the strains placed upon the chip within the context of a 9v power source (whather battery or wallwart). And, as noted earlier, ultimately, the tone you hear is a function of what the pedal does to the amp and what the amp does to the speaker. So, the diodes certainly play a role, but they are not absolutely pivotal in what it is you get to hear at the end.


 And slightly related, Mark have you seen this Visual Sound video:

[youtube]bpTv2jAree8[/youtube]

That only applies to a design that runs the opamp in the ideal operating range, where you're not pushing it to amplify to the very limits of its rails. But interesting nonetheless.


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## keeperofthegood

Mark, Ian!! Great posts guys!

To illustrate that components OTHER than the diodes shape the wave, and affect the gain, have a study of this. This is using diode feedback, clipping, symmetrical integration (that is what the capacitors in the feedback are about):










In the first circuit A you will essentially see your basic amp. In this case the capacitors are non-functional being bypassed by 150K resistors which are part of the feedback gain loop. 

In the second, third and fourth circuits I removed the 1 ohm open-loop resistances, and replaced those with diodes.

I didnt work out the resistance of the diodes, so there is a gain increase of them VS the 1 ohm resistor. In using a purely resistive feed back loop, the diodes do not alter the wave shape as seen in B

In C Adding in the capacitors instead of the resistors and making the feedback an integration loop instead does cause a distortion of the output, this should have lots of BUZZ being more like a full square wave.

Letting the caps have a "discharge path" as in D and adding the resistors back, the distortion becomes softer.

Here is the code, play with this. Let me know if you build it and how it goes. I would, but I tend to good op-amps >.< I'm really sucktackular at op-amps and 555 timers >.< Ive burned so many up.


$ 6 4.9999999999999996E-6 0.0 50 5.0 50
R 88 336 88 288 0 1 100.0 0.08 0.0 0.0 0.5
r 304 424 304 568 0 100000.0
c 208 280 304 280 0 2.2E-7 0.025013695409271897
c 208 328 304 328 0 2.2E-7 0.025013695409271897
a 128 424 304 424 0 4.5 -4.5 1000000.0
w 304 280 304 328 0
w 128 280 128 328 0
g 128 440 128 472 0
g 304 568 304 600 0
r 128 408 128 328 0 100000.0
r 88 336 88 408 0 10000.0
r 208 360 304 360 0 150000.0
r 208 232 304 232 0 150000.0
w 304 424 304 360 0
w 304 360 304 328 0
w 304 280 304 232 0
w 208 328 208 360 0
w 208 280 208 232 0
r 208 280 128 280 0 1.0
r 208 328 128 328 0 1.0
r 408 408 408 328 0 100000.0
g 568 568 568 600 0
g 408 440 408 472 0
w 408 280 408 328 0
a 408 424 568 424 0 4.5 -4.5 1000000.0
d 472 328 408 328 1 0.205904783
d 408 280 472 280 1 0.205904783
r 568 424 568 568 0 100000.0
r 360 336 360 408 0 10000.0
R 360 336 360 288 0 1 100.0 0.08 0.0 0.0 0.5
w 360 408 408 408 0
w 128 408 88 408 0
w 632 408 680 408 0
R 632 336 632 288 0 1 100.0 0.08 0.0 0.0 0.5
r 632 336 632 408 0 10000.0
r 840 424 840 568 0 100000.0
d 680 280 744 280 1 0.205904783
d 744 328 680 328 1 0.205904783
c 744 280 840 280 0 2.2E-7 2.1994804746853216
c 744 328 840 328 0 2.2E-7 -2.088429278415292
a 680 424 840 424 0 4.5 -4.5 1000000.0
w 840 280 840 328 0
w 680 280 680 328 0
g 680 440 680 472 0
g 840 568 840 600 0
r 680 408 680 328 0 100000.0
w 840 424 840 360 0
w 840 360 840 328 0
w 840 280 840 232 0
w 744 328 744 360 0
w 744 280 744 232 0
x 268 503 283 509 0 24 A
x 526 501 542 507 0 24 B
x 800 500 817 506 0 24 C
x 12 640 27 646 0 24 A
x 268 643 284 649 0 24 B
x 523 646 540 652 0 24 C
x 393 263 459 266 0 12 Germanium
x 157 532 289 535 0 12 100K output Resistance
x 11 423 129 426 0 12 10K Input Resistance
x 46 253 144 256 0 12 80mv Input Signal
x 667 258 733 261 0 12 Germanium
w 568 280 568 232 0
w 568 360 568 328 0
w 568 424 568 360 0
r 472 232 568 232 0 150000.0
r 472 360 568 360 0 150000.0
w 568 280 568 328 0
w 472 280 472 232 0
w 472 328 472 360 0
x 931 258 997 261 0 12 Germanium
x 1064 500 1081 506 0 24 D
w 1008 280 1008 232 0
w 1008 328 1008 360 0
w 1104 280 1104 232 0
w 1104 360 1104 328 0
w 1104 424 1104 360 0
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r 1008 360 1104 360 0 150000.0
r 944 408 944 328 0 100000.0
g 1104 568 1104 600 0
g 944 440 944 472 0
w 944 280 944 328 0
w 1104 280 1104 328 0
a 944 424 1104 424 0 4.5 -4.5 1000000.0
c 1008 328 1104 328 0 2.2E-7 -0.349845532034432
c 1008 280 1104 280 0 2.2E-7 0.3998690123819868
d 1008 328 944 328 1 0.205904783
d 944 280 1008 280 1 0.205904783
r 1104 424 1104 568 0 100000.0
r 896 336 896 408 0 10000.0
R 896 336 896 288 0 1 100.0 0.08 0.0 0.0 0.5
w 896 408 944 408 0
x 782 644 799 650 0 24 D
o 1 32 0 290 1.1692013098647223 1.1417981541647679E-5 0 -1
o 27 32 0 290 3.8272525864510487 3.737551353956103E-5 1 -1
o 35 32 0 290 4.091738259870177 3.9958381444044705E-5 2 -1
o 89 64 0 290 2.187250724783012 2.1359870359209102E-5 3 -1


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## mrfiftyfour

Daaammmnnn!
Ask a simple question!
This forum deserves a gold medal!


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## keto

I actually tried it tonight. Only briefly, only with 1 guitar and 1 amp. See here: http://www.guitarscanada.com/showthread.php?31757-World-s-Smallest-Fuzz Didn't like the LED as much in this particular circuit, it was muyo bright and looser than the diode clipping.


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## mrfiftyfour

If you let me know what you were thinking of installing the LEDs in, I could probably provide some guidance on what to expect, and whether it's a good idea or not. As with any sort of modification, context is very important.

Thanks for that post, mhammer.
If you recall, a couple of months ago there was a thread about the Dist+ and we were discussing different mods.
http://www.guitarscanada.com/showthread.php?21095-Thoughts-on-MXR-Distortion-Vintage-vs.-Reissue
I have to admit, I'm obsessed with the Dist+. I'm convinced the Dist+ has "my" tone in it and it just needs a little tweeking. 
I'm definitely not looking for any clean tones 'cause I'm a total rock pig and I'll be using the pedal with an amp set to light gain for the cascading effect. 
So as Wild Bill says, if I like the distortion, I shouldn't change the diodes.

As mhammer stated, I should play with the amount of gain hitting the diodes.


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## mhammer

Okay.

T'wer I, I wouldn't bother with LEDs in a Dist+. I would *maybe* go as far as a 2+2 pair of silicon diodes, but that's about it. A pair of LEDs is going to drift farther away from a Dist+ sound than you probably want.

Certainly try it out if you have the parts and there is no risk of damaging the rest of the circuit or board, but I am personally not expecting miracles.

What exactly did you want the pedal to do "more" of?


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## mrfiftyfour

mhammer said:


> Okay.
> 
> T'wer I, I wouldn't bother with LEDs in a Dist+. I would *maybe* go as far as a 2+2 pair of silicon diodes, but that's about it. A pair of LEDs is going to drift farther away from a Dist+ sound than you probably want.
> 
> Certainly try it out if you have the parts and there is no risk of damaging the rest of the circuit or board, but I am personally not expecting miracles.
> 
> What exactly did you want the pedal to do "more" of?


I'd like to add some girth, ya'known?
Deeper and fuller sounding.
It's hard to put into words, but more 3 dimensional


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## keeperofthegood

mrfiftyfour said:


> I'd like to add some girth, ya'known?
> Deeper and fuller sounding.
> It's hard to put into words, but more 3 dimensional


Hmm, almost sounds like you are looking for a little reverb or echo. I will be interested in Mark's reply to this, if it would be a matter of a second pedal or a mod to the pedal you have now.


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## mhammer

mrfiftyfour said:


> I'd like to add some girth, ya'known?
> Deeper and fuller sounding.
> It's hard to put into words, but more 3 dimensional


Well, one needs to be realistic in one's expectations of a lousy op-amp and a couple of diodes.. You can spruce up KD in *lotsa* ways, but it will never be filet mignon.

The "heft" of the tone will be improved by replacing the .047uf cap in series with the gain control with a larger value, like .22uf. That will assure that the same gain applied to the mids at max drive is also applied to the bass. If the frizziness of the pedal is objectionable, then you stick a cap in parallel with the 1M feedback resistor. 100pf rolls off above roughly 1600hz, 47pf rolls off above 3.4khz. Frizziness is often what obstructs a distortion from sounding "3-D" to some ears, since the notes get lost amidst all the harmonics of harmonics.

Use of LEDs will place the brunt of the pedal's tone squarely on the shoulders of the 741 chip. While its distortion of the signal is used to push the (normally stock) germanium diodes into a more pleasing clip, if most of the distortion at most gain settings comes from the 741, it won't likely be pretty.

Mine has the above changes, plus a germanium/silicon switch, as noted earlier. I also have a SWTC between the clipping diodes and output level control. This is a very simple sort of tone control that rolls off highs without producing noticeable changes in output level. In the Dist+ context, that consists of sticking a 470R-1k fixed resistor in series with a 10k pot just before the volume control in the manner shown at the start of this article: http://www.muzique.com/lab/swtc.htm Jack Orman extends this simple principle in some interesting and clever ways.

Other things to consider are use of MosFets as clipping elements as in the Shaka Braddah series: http://www.muzique.com/schem/shaka5.gif


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