Diode types

[Audiowonderland]

Looking at a new build. Based on my most recent experience LED's seem to have a fatter, smoother tone than the more standard silicon diodes commonly used. WHere does the germanium diode fit in all of this? I am looking at using switchable clipping between LED's and Germaniun diodes. From what I have read germanium is fatter /smoother than silicon diodes. Is this the case? What are the differences sonically between the various color LED's? How does the size of the LED impact the sound? ie 5mm vs 3mm LED's?

Any insight on this is appreciated..

[Greg]

Sorry for the serious answer.. but:

Diodes don't have any tone as such.. they're just a simple semiconductor component that conducts current in one direction and blocks it in the other, and they require a certain forward voltage (which varies depending on type), before they begin to conduct.

How they sound will depend on the circuit they're in, and how they're used in that circuit..
Clipping to ground will have a different effect to clipping in a feedback loop.
They do have some effect on tone (or perceived tone), and also on the voltage swing and level of compression.. again depending on type.

The higher the forward voltage (Vf), the less they'll limit or compress, and that's the best predictor of how they'll perform.
The other factor is the rate at which they begin to conduct when forward biased (sometimes called the conduction curve or knee).

Germaniums = 0.2 to 0.3 Vf
Silicon = 0.6 to 0.7 Vf
LEDs = 1.5 to 3.0+ Vf

[Audiowonderland]

Sorry for the serious answer.. but:

Diodes don't have any tone as such.. they're just a simple semiconductor component that conducts current in one direction and blocks it in the other, and they require a certain forward voltage (which varies depending on type), before they begin to conduct.

How they sound will depend on the circuit they're in, and how they're used in that circuit..
Clipping to ground will have a different effect to clipping in a feedback loop.
They do have some effect on tone (or perceived tone), and also on the voltage swing and level of compression.. again depending on type.

The higher the forward voltage (Vf), the less they'll limit or compress, and that's the best predictor of how they'll perform.
The other factor is the rate at which they begin to conduct when forward biased (sometimes called the conduction curve or knee).

Germaniums = 0.2 to 0.3 Vf
Silicon = 0.6 to 0.7 Vf
LEDs = 1.5 to 3.0+ Vf

No worries about being serious. That's great information and information is what I am missing being a very green newb at all of this. I will need to revisit the circuit of my last build to see if the LED and silicon diodes are handled the same way. It may just be that what I am hearing is the effect of the LED's having a significantly higher forwarding voltage resulting in a lot less distortion and I would presume a lot fewer upper harmonics.


I believe I have read that diodes in series increase the forwarding voltage. Is that correct?

[deltafred]

Yes, diodes in series you add the forward volts drops together.

As you say LEDs having a much higher forward voltage drop will require a lot more gain than a single or even 2 series silicon diodes to get to the same distortion level.

[Audiowonderland]

Yes, diodes in series you add the forward volts drops together.

As you say LEDs having a much higher forward voltage drop will require a lot more gain than a single or even 2 series silicon diodes to get to the same distortion level.

I definitely don't want Germaniums in my DS-1 mod then. Definitely LED's there I think.

How much if any does the color of the LED make? Is that simply a function of the forwarding voltage or it its simply a cosmetic thing?

[deltafred]

I definitely don't want Germaniums in my DS-1 mod then. Definitely LED's there I think.

How much if any does the color of the LED make? Is that simply a function of the forwarding voltage or it its simply a cosmetic thing?

I am sure someone with DS-1 experience will advise you on what works and doesn't.

The different colours have different volt drops, there is a table about 2/3 way down this page

http://www.kpsec.freeuk.com/components/led.htm

Be aware that the VF quoted is for quite high current required for normal brightness and will reduce slightly at the lower current as used for clipping diodes.

[Audiowonderland]

I definitely don't want Germaniums in my DS-1 mod then. Definitely LED's there I think.

How much if any does the color of the LED make? Is that simply a function of the forwarding voltage or it its simply a cosmetic thing?

I am sure someone with DS-1 experience will advise you on what works and doesn't.

The different colours have different volt drops, there is a table about 2/3 way down this page

http://www.kpsec.freeuk.com/components/led.htm

Be aware that the VF quoted is for quite high current required for normal brightness and will reduce slightly at the lower current as used for clipping diodes.

Thank You. Much Appreciated.

[merlinb]

LEDs and Si diodes give basically the same 'hardness' of clipping, they just do it at different levels. The fact that you need more voltage swing to get an LED to clip may mean that other parts of the circuit start to sound different due to slew limiting etc. It also means you get a bigger signal level and therefore lower noise.

Ge diodes clip a BIT more softly, and at a lower voltage. Not as softly as some people like to pretend, though.

[deltafred]

Ge diodes clip a BIT more softly, and at a lower voltage. Not as softly as some people like to pretend, though.

Great graph there merlinb.

On the Ge clipping softer thing. If you normalised the voltage (which is what you do in a pedal, with a suitable amount of gain after the clipping stage) then the Ge will be a whole lot softer than any of the others.

[merlinb]

On the Ge clipping softer thing. If you normalised the voltage (which is what you do in a pedal, with a suitable amount of gain after the clipping stage) then the Ge will be a whole lot softer than any of the others.

I suspect your idea of "a whole lot softer" is my idea of "a bit softer". But then, I'm used to dealing with vacuum diodes, which are a whole lot softer...

[deltafred]

On the Ge clipping softer thing. If you normalised the voltage (which is what you do in a pedal, with a suitable amount of gain after the clipping stage) then the Ge will be a whole lot softer than any of the others.

I suspect your idea of "a whole lot softer" is my idea of "a bit softer". But then, I'm used to dealing with vacuum diodes, which are a whole lot softer...

As you say vacuum diodes are 'a whole lot softer' than either Ge, Si or LEDs.

I haven't used a distortion pedal in years so have no idea how they sound, I suspect that the tone controls makes the most difference. The last one was a Marshall Guvnor clone which used red LEDs. It would be interesting to do a comparison between Ge, Si and LEDs to see if there is much appreciable difference (leaving the tones controls set the same of course).

I play bass most of the time now through an SFT clone so I am now using overdriven FETs.

[Audiowonderland]

On the Ge clipping softer thing. If you normalised the voltage (which is what you do in a pedal, with a suitable amount of gain after the clipping stage) then the Ge will be a whole lot softer than any of the others.

I suspect your idea of "a whole lot softer" is my idea of "a bit softer". But then, I'm used to dealing with vacuum diodes, which are a whole lot softer...

As you say vacuum diodes are 'a whole lot softer' than either Ge, Si or LEDs.

I haven't used a distortion pedal in years so have no idea how they sound, I suspect that the tone controls makes the most difference. The last one was a Marshall Guvnor clone which used red LEDs. It would be interesting to do a comparison between Ge, Si and LEDs to see if there is much appreciable difference (leaving the tones controls set the same of course).

I play bass most of the time now through an SFT clone so I am now using overdriven FETs.

The Guv'nor clone I have has the red LED's and N914 diodes that are switchable with a toggle for clipping. LED = fatter and smoother. Si Diode's = brighter and a bit crunchier than the LED with all settings being the same. I prefer the LED's

[FiveseveN]

with all settings being the same.

The controls might be set the same but the circumstances are not! As someone mentioned before, the voltages need to be "normalised". The input signal (gain) needs to be about 3 times higher and the output level (volume) needs to be about 3 times lower so the ratio of signal level vs. forward voltage stays the same.

[Audiowonderland]

with all settings being the same.

The controls might be set the same but the circumstances are not! As someone mentioned before, the voltages need to be "normalised". The input signal (gain) needs to be about 3 times higher and the output level (volume) needs to be about 3 times lower so the ratio of signal level vs. forward voltage stays the same.

I hear what your saying and agree if we are talking about a strict comparison of the sonics of the LED vs the sonics of the Si Diode. In the real world though those variables are not even a thought to the player when they plug in and flip back and forth between the 2 options and decide what they like better. Hell I barely understand it but I am learning. Some will like the brighter, more distorted option the Si diodes give and others will prefer the fatter, less distorted results of the LED's. Its those perceptions that I think I will need to address when I put something in front of another player to tryout for feedback. Would you agree?

[FiveseveN]

Like Greg_G, there's no such thing as "diode sonics". You're talking about the characteristics of an entire circuit in which some variables are switched.
There could very well be a circuit which compensates for the different forward voltages, as I described. There could be a thousand circuits where the type of diode makes absolutely no difference. In order to learn something about what happens with our signal we must look at the issue in context. And then there's aesthetics, which is an entirely separate set of queries.
You have to ask the right question.