Soft clipper explanation, plskthnx [Kingslayer content]

[midwayfair]

Is the reason that the Kingslayer shouldn't have Ge soft clippers that it would drop the signal too much to trigger the hard clippers, or something else? Obviously it's not an inherent property of soft clippers because Ge makes its way into tubescreamers all the time.

I've got a pretty good handle on hard clipping, but soft clipping is a pretty nebulous area for me. If someone has some required reading, please share a link.

[JakeFuzz]

Soft clippers can be understood by going through the op-amp rules and how the diode behaves before and after the forward breakdown voltage. If we think that an op-amp only wants to equalize the signals on its inputs, we can see that before the diodes breakdown voltage we will just be amplifying the signal on the input. After breakdown though (lets say 0.7 volts) the diode acts like a short (well with a constant 0.7 volt drop across it and the feedback resistor). This 0.7 volt drop across the feedback resistor acts like a constant "bias" current feeding into the junction between the diodes and the input of the amp. Because the diode acts like a short above its forward voltage it makes the amp look like a unity gain buffer. So what we get is the amplified signal up to the forward voltage after which we get unity gain which rides along a DC bias of wherever the top of our original signal clipped.

The unity gain helps to smooth out the clipping shoulder transition and makes a "softer" sounding overdrive IMO. What is interesting about this setup is that the clipping gets less soft, if that makes sense, as the gain of the amp increases away from 1. This is because the gain is so much higher than unity that the unity gain "ride-along" looks almost flat.

As for Ge's; I think they just make the clipping shoulder transition a little slower and probably smooths it out a bit. I would also say the slew rate of the amp has an affect on this transition shoulder as well although how much I couldn't say for sure. I have tested several soft clippers in the Kingslayer and found that it can get a little fizzy and muddy with really low Vf diodes. I think something like our OA126's would be perfect in there. Ill try it when I get home from vacation!

[midwayfair]

Thanks so much for the detailed explanation. I really appreciate it. It also helped me understand why feedback loop diodes result in so much more compression than hard clippers.

As for Ge's; I think they just make the clipping shoulder transition a little slower and probably smooths it out a bit. I would also say the slew rate of the amp has an affect on this transition shoulder as well although how much I couldn't say for sure. I have tested several soft clippers in the Kingslayer and found that it can get a little fizzy and muddy with really low Vf diodes. I think something like our OA126's would be perfect in there. Ill try it when I get home from vacation!

I noticed the fizziness, too, but I really wasn't sure if it was just a sound reason or electronics reason. I ended up with Mosfets for the moment to get more variety, but I'm not completely sold on them. I can say what I really wish I had: One side clipping at 4.5 and the other clipping at 9. I can make the second but the first ... I can't think of anything that clips in that range. I guess I'd have to make it.

[JakeFuzz]

I like to write these things out because it helps me to understand whats going on as well. Sometimes just talking through it helps me realize things I never see normally.

Fizziness is an interesting beast. Fizziness is usually due to an excess of high order harmonics. The harder the sine wave clips (pretty much turns into a square wave) the more higher order harmonics are generated. If we just listen to a square wave it has tons of crazy fizziness and nastiness. If we actually take the Fourier transform of a perfect square wave we see it is made up periodic signals of every frequency. This is why we can reconstruct a frequency response from an impulse response function. More useful is measuring the frequency response, doing a fast Fourier transform and using a convolution integral (made up of many little impulse response functions) to get the response of a linear system to any arbitrary input. Square waves = love/hate; good for engineering, bad for guitar. As we round out the corners of the the square wave though we start to get less and less of these higher order harmonics of the fundamental frequency; Eventually we round it out so much that we get back to our pure sine wave which has only the fundamental frequency and no harmonics at all.

It gets even more interesting when we start to filter before and after clipping or combining the two types of clipping... And that's why I have more overdrives and fuzzes than anything else on my board