Difference in clipping diodes?

[BowerR64]

Im new and have a few questions about diodes. Ive been tinkering with a few cheap amps (Marshall MG10CD and the First Act MA104) the Marshall uses 1 green and 1 red clipper diode where the First act uses 4148 diodes.

I swapped them thinking the Diodes would sound better in the Marshall but i dont hear much difference. I then started to wonder about other LEDs that i have. I bought these super bright white LEDs to use as a camera light ring some years ago. When i hook 3 volts to them they come one but not near as bright as when hooked to 6v i think these are actually 6v LEDs

So my question is, whats the difference in 3v LEDs and 6V when used as clipper diodes? Would the 3V LEDs clip before the 6V?

Also is there any difference in sound between diodes and say a 6 pin opamp type of chip? What if i tap off the 15V line in the MG10 and use that to power a small opamp chip and use the opamp insted of the LEDs? Or can i even do that?

I think what im looking for is a slower clipper, one that is the most tube like of the others? light pick attack little or no distortion then more pick attack starts to distort.

Any help is great.

[Brisance]

Mosfets are softer, when you wire them back to back

[bool]

Try the bigger 10mm dia LEDs. They have larger junction capacitance. Or just wire in a series resistor for softer action.

[FiveseveN]

What does "softer" mean?

whats the difference in 3v LEDs and 6V when used as clipper diodes? Would the 3V LEDs clip before the 6V?

Yes, that's the main difference between diodes when used for clipping: lower forward voltage means "earlier" clipping, e.g. more saturation if everything else stays the same. The absolute amount of saturation also depends on how much gain is applied beforehand and filtering is also crucial to a circuit's "sound". E.g. those tiny speakers will determine most of the amps' "character" through their small bandwidth.
Diodes and operational amplifiers (though I don't remember ever seeing one in a 6 pin package) are completely different devices. Though one can use different means to achieve similar results, yanking out random parts of a working circuit and replacing them with other random parts is generally not worthwile.
I suggest you take a systematic approach to learn what everything does, starting with the excellent Beginner project and articles like this primer on distortion.

[BowerR64]

Well the amp already has to much distortion stock so i added a resistor inline with the gain to the clipping diodes and that helped alot allowing me to turn the gain dial up more before it to distorted.

I cut the amp cabinet down and wired in an output jack so im not using the stock speaker, im running it into a 4X12 so it sounds WAY better then it does stock.

Using the amp i already have built i just swap in and out the diodes to hear the sound. The smaller 3V LEDs that came with the amp seem to have the quickest breakup and the LEDs reach their max brightness way earlier then the larger 6V. The 6V will light up but they dont get even close to what they can do on 6V

I bought some 3V amber 5mm LEDs and tried them and wow they are weird, the amp is alot louder with them in and the distortion is more clean then with any of the other LEDs

[antonis]

the distortion is more clean then with any of the other LEDs

I'm not sure if you use the word "clean" for qualitative or quantitavive purpose..

[merlinb]

If you want soft clipping then using different silicon diodes or LEDs doesn't help very much. Yes they have different clipping thresholds, but they all clip pretty much with equall 'hardness' once you reach that threshold. You simply need different amounts of gain to get there.

For softer clipping you're best bet is to use Germanium diodes, possibly several in series if you don't want to alter the gain. A ladder array of silicon diodes could also work, but needs more parts.

[vigilante397]

Not sure how relevant this is to the OP's question, but I stumbled on this gem a few days ago when investigating diode options for an overdrive I built recently.

Obviously not my work, but the work of forum member Jon (midwayfair)

http://music.codydeschenes.com/?p=1615

[Mark Hammer]

1) When using LEDs as a diode (rather than an illumination source), their diode/clipping action may be accompanied by lighting up, but does not need to be.  Plenty of folks will tell you that circuits they have made, using red LEDs for clipping have clipped just fine, without any visible signs of the LEDs "turning on".

Having said that, if you use "superbright" LEDs, since they require less current to deliver visible illumination, the odds are greater that clipping and lighting up will go hand in hand.  BUt it won't necessarily be bright.

2) "Softer" clipping is usually provided by having a small resistance in series with the clipping diodes.  "Small" would be any of a variety of values in the 47R-1k range.

3) Different coloured LED have different forward voltages.  Red is generally the lowest Vf of the lot, coming in around 1.5-1.7V, with green typically higher.  Use of a Red+Green pair is intended to provide asymmetrical clipping, analogous to the use of a 2+1 diode combo, or Mosfet/Mosfet+diode combo, albeit at a different range of forward voltages.

[BowerR64]

the distortion is more clean then with any of the other LEDs

I'm not sure if you use the word "clean" for qualitative or quantitavive purpose..

Well what i mean by clean is with an LED that is say 3v forward voltage i can pick the guitar soft and it sounds some what clean and then hit it with a more agressive picking attack and it then starts to break up and distort simmilar to a tube IMO.

The stock diodes red and green i cant do this with. They break up instantly and no matter how soft or light you pick its dirty.

I soldered in a servo connector from an R/C servo and this lets me poke in different diodes and LEDs its crazy how some diodes can really rob the volume. If i use no diodes the amp is super loud and it seems the more gain or clipping the diode gives the lower the volume i get from the amp.

I have these amber LEDs i got off e-bay they are 3v (2.2-3.3v) and so far they have the best sound most realistic tube sort of characteristic IMO of any other ive tried so far.

What does stacking them do? i dont think ive tried that yet.

[teemuk]

1. This topic really should be stickied
2. You really should learn to use the search function

Anyway....

Well what i mean by clean is with an LED that is say 3v forward voltage i can pick the guitar soft and it sounds some what clean and then hit it with a more agressive picking attack and it then starts to break up and distort simmilar to a tube IMO.

The stock diodes red and green i cant do this with. They break up instantly and no matter how soft or light you pick its dirty.

That's the point of talking about forward voltages and such. If Vf is lower clipping is earlier. Try to "normalize" signal levels going to the clipping cell so that the 3V LED, red LED and green LED all clip the signal in approximately same ratio. At that point you probably won't notice much difference in between them. Altering gain/attenuation is much easier than trying to find an ideal device that works in right forward voltage range.

Forward voltage is just one parameter. It's virtually similar to "speakewr impedance", meaning that in real life the quoted value is just "nominal". In practice, you can draw forward voltage as a curve. Like this:

You'd be interested in overall curvature and the "angle". These matter more than Vf because the particular characteristics is much harder to compensate externally. In practice you may find widely different angles from all kinds of diodes whereas their forward voltage might be in slightly different range. The usual simplified idea is akin to this:

Real life is this:

Note that e.g. AA112 and 1N34A are both Germanium diodes but in practice their forward characteristics are quite different. Except for lower Vf the 1N34A behaves almost like a silicond diode 1N914.

I have posted this stuff to several threads about clipping diodes. This is the last one. I'm no longer wasting time or bandwidth to folks too lazy to search.

I soldered in a servo connector from an R/C servo and this lets me poke in different diodes and LEDs its crazy how some diodes can really rob the volume. If i use no diodes the amp is super loud and it seems the more gain or clipping the diode gives the lower the volume i get from the amp.

It's clipping. It clips off signal peaks, hence the name. That means the amplitude of signals is limited to clipping voltage. Without normalizing signal levels post clipping it's going to be different loudness level than unclipped signal, especially if the "clean" signal path simply switches diodes off the signal path. That's why good clipping units (whether amps or effects) have controls to balance clean and distorted levels.

[merlinb]

The stock diodes red and green i cant do this with. They break up instantly and no matter how soft or light you pick its dirty.

That simply means you have too much gain before (or in) the clipping stage.

If i use no diodes the amp is super loud and it seems the more gain or clipping the diode gives the lower the volume i get from the amp.

That means you need more gain after the clipping stage, to bring the signal level back up to the same level as without the diodes.

[merlinb]

Forward voltage is just one parameter. It's virtually similar to "speakewr impedance", meaning that in real life the quoted value is just "nominal". In practice, you can draw forward voltage as a curve. Like this:

The example image you posted is actually a bit misleading, as it implies that green/blue/white LEDs clip waaay softer than infra-red/red/amber. They don't. Here are some actual measured characteristics:

[antonis]

If i use no diodes the amp is super loud and it seems the more gain or clipping the diode gives the lower the volume i get from the amp.

Nothing strange here...

Without diode clipping you drive "clean" signal to your amp (already distorted or not - depenting on your previous amplification..)

With diode clipping you drive to your amp a signal with maximun level what is your diode's forward voltage..

If Dfv is equal or higher than signal's level you will have no volume drop (and no clipping too..)
If Dfv is lower than signal's level you will have some volume drop (the amount of drop will be the difference between the two voltages..)

e.g. If you use a white led to clip a signal coming from an op amp biased at 4.5V (Vcc 9V and Vee GND) you will actually get NO clipping...
(according to teemuk's graph...)

[BowerR64]

I did try and search but i couldnt figure out what section to search. Its really not as easy as just doing a search when you dont even know the correct terminology it may seem simple if you know the board but this one seems slightly different.

I searched google first and it lead me here but not to the right area or i would not of started another topic.

If there was a sticky on the common asked questions it would help the forum too because it would lead traffic here when they use google like i did.

Thank you for your help the 2 images on the LEDs helped now im going to try the other LEDs i have i didnt know white and blue what that much further back. I did try the infra red also