CURIOUS CORNER

This is a space for the curious, who wonder how things work and then try to discover. Thanks for taking a peek into the corner of curiosity. I hope you will visit again soon and find a delectable tidbit of knowledge that has satisfied some of our own excited and curious wondering...

THE BEST OF BOTH WORLDS

Why do music lovers love electron tubes, and how do these tubes work? Why do silicon-based transistors sound different from tubes, and is it possible that a silicon semi-conductor can reproduce a sound as good as an electron tube can? Today in the Curious Corner, let's take a look into how electrons passing through different devices can make really nice sounds. Let's start with a quick explanation. If you'd like a more detailed explanation, click on the picture below. Scroll down beyond the picture to keep reading. There's an audio recording down there that provides an interesting example!

An electron tube can amplify an alternating audio signal by using the audio signal to turn on and off the flow of electrons between a stick of metal (the cathode) that supplies electrons and a charged metal plate that absorbs electrons. In between these metal surfaces is a "grid" of tiny wire. The electric audio signal is passed into this grid between the electron supply and the plate (where the electrons want to go). The audio signal in the grid acts like a traffic light: when its voltage is positive (green light), lots of electron traffic flows from the cathode source to the plate (from which the amplified audio signal is taken); when the grid voltage is neutral (yellow light), less electron traffic passes onto the plate; and when the grid voltage is negative (red light), only a little electron traffic passes onto the plate. What is great about tubes is that the passage of electrons by an alternating (positive-negative) audio signal is very smooth. Using the traffic light analogy, there is virtually no "slamming on the brakes" or "screeching tires". Everything happens smoothly, even with extremely fast (high frequency) audio signals. Since an electron tube can handle very slow (low frequency) signals as well as extremely high frequency signals very well, the sounds that they reproduce are very pleasing to the human ear. 

Silicon-based transistors are a little different. For those who would like to learn more, click on the following link for an interactive animation of the bipolar junction transistor, a popular audio transistor: Silicon Transistor Operation

If left alone, a semi-conductor like silicon will not conduct electricity. It acts as an electric insulator. But if the silicon crystal lattice is given a treatment with other chemical elements (doping), it can have regions that supply enough electrons to conduct a current. If 2 of these regions are separated by a region of plain silicon, then when an electric field is applied across the "doped" silicon region, the entire silicon lattice will conduct electric current. This is a simplified explanation, but it illustrates the basic operation of a silicon transistor. Like a tube's control "grid" (that controls the flow of electron traffic), the transistor needs a control mechanism, which is the electric field. When an audio signal is used to control the strength of the electric field applied to the silicon lattice, the field acts like a traffic light. But unlike electron tubes, the flow of electron traffic inside a transistor is not so smooth. When the electric field turns on the flow of electrons (and when it turns things off), there can be quite a bit of "screeching tires" and "slamming on the brakes". The transitions can be quite violent compared to those inside an electron tube, and human ears can hear this difference. Not all silicon transistors are created equally, however. Some are a lot more violent than others, and some can be rather smooth when joined with the right parts.

So what is the solution to the transition problem? Why not just stick with tubes since they are so smooth? Well, transistors have come a long way, and some of them have a very fine sound, every bit as good as a tube. Thanks to the evolution of manufacturing techniques, a lot of those violent electrical transitions inside transistors are so quiet that human ears cannot hear them. And when an audio signal is amplified first by a transistor and second by a tube, the tube smooths out every one of those "violent" transitions. The electron tube smooths things out and rounds off all the sharp corners. To illustrate this and to introduce a new question, here is an audio example. In this example you can hear an electric guitar being amplified by an all-tube Mesa/Boogie guitar amplifier. Before the guitar signal was amplified by the guitar amplifier, it was amplified a little bit by several silicon transistors inside guitar pedals like the Ibanez Tube Screamer (2 of them back-to-back in this recording). This recording is an improvised rendition of a game show theme song, the old $25,000 Pyramid game show. Interestingly, when you press play and hear the song, it will be amplified by many silicon transistors in your computer or phone before entering your ears. Continue reading after the song for a conclusion to today's Curious Corner. If a transistor amplifies a sound that has been amplified by a tube, will the pleasing sound of the tube still be heard?

The electric guitar sound in the recording started in the pickups of my guitar as a pure electric signal caused by the guitar strings vibrating in the magnetic field of my guitar's pickups. It was then amplified by several silicon transistors in my guitar pedals, where it was made louder and gained some violent electrical transitions. Then the guitar signal went into an all tube guitar amplifier, where it was made even louder and those violent transitions were smoothed out. Along the way some "pleasing coloration" was added to the sound of my guitar  by both the transistors and the tubes. The sound from the guitar amplifier was picked up by a microphone and passed through even more transistors and converted to a digital audio signal before it was recorded on my computer. Then if you clicked "play" above, it was downloaded to your device and converted back to an analog audio signal by a multitude of transistors before it entered your ears. You can see that there are far more transistors in this process than tubes, yet the pleasing sound produced by the tube guitar amplifier can still be picked out and enjoyed. For an awesome example of transistors driving tubes, check out this demo video:

We can't change the laws of nature, but we can discover new ways of reproducing sounds that are highly pleasing to the ear. As technology continues to evolve, the transistor may not only catch up to the tube (it already has), it may go the way of the tube and be used primarily in audio amplifiers. JJJ Engineering is committed to finding the devices that work best to deliver only the most pleasing sounds. We love good tubes, and we love good transistors, and we really love good tubes being driven by good transistors. The truth is that these devices can get along just fine-- they aren't mutually exclusive, and today one is not better than the other (unlike yesterday). Tomorrow both tubes and transistors will be surpassed by new technology, and tomorrow will be here sooner than we think! 

Thanks for stopping by the Curious Corner. If you have any comments, suggestions or questions, feel free to drop an email to jc@ampedinnovations.org. 

-- Jack III