Picking Up the Pieces
Hello Troubadourians! In an earlier column, I wrote about a phenomenon common to tube-based amplifiers where they have a “sweet spot,” which is the minimum volume that the amplifier can operate and still deliver a full spectrum of tonality. Some people call it “bloom” or “blend,” terms that are actually more apt from an electronics perspective than most musician slang because the phenomenon, when viewed on an oscilloscope (an instrument used to test and measure the performance of electronic circuits), the frequency response of the amplifier changes visually as well as audibly. The traces of the oscilloscope do indeed seem to bloom and blend into a more cohesive pattern. While the math and physics that we would use to explain the sweet spot in an amplifier is fairly complex; we can essentially say that this is the point where all of the active components in the circuit begin to interact harmoniously instead of randomly.
When that column was published, someone wrote to me and asked if electric guitars do the same thing. The short answer is: yes, they do. The longer answer is: yes, but in an entirely different way for entirely different reasons and with lots more moving parts. In this column, I’ll try to explain what that means in terms that are accurate electronically and physically but still make sense to any musician who just wants to know how an electric guitar actually works.
Setting aside for now the fact that an electric guitar is still an acoustic guitar at its most basic level, what makes an electric guitar “electric” is its pickup or pickups. So, what are pickups and where are they located? Pickups are electronic devices that are located under the strings in between the end of the fretboard and the bridge. Pickups function inductively, which means that they are constructed of a combination of magnets and wire coils and use the vibration of the strings in close proximity to “induce” a current to flow in the coils, which in turn creates a voltage that changes with the frequency of the vibrational frequency of the string. This, then,Â is passed to the amplifier where the tiny voltage is amplified into sound of a usable, audible level. Got all that? Okay, let’s break it down a little more; in analog electronics there is a device called an inductor. It is considered to be a passive device because it requires external stimulus to function. While there are several ways to construct an inductor, the simplest method consists of a coil of wire surrounding some type of ferrous material. (Ferrous means that it contains iron). This is the basic construction used in most electric guitar pickups. A very simplified explanation of what occurs in a pickup is that the movement of the string disturbs the magnetic field that surrounds the magnet, which in turn induces a current to flow in the coil of wire. Current and voltage are related (no, I’m not going to explain how in this column because it would take too much space and is irrelevant to the specific point of explaining that pickups have a sweet spot), so where you have one, you also have the other and it is this voltage that becomes sound in your amplifier.
The pole pieces of a pickup can be adjustable or in a fixed position. Likewise, they can be magnetic or non-magnetic. If they are non-magnetic, they will most likely be in physical contact with a magnet as part of the construction of the pickup. The actual magnet will share its magnetic properties with the non-magnetic pole pieces (which are usually screws that are either threaded into or otherwise in direct contact with a magnet). Just as with amplifiers, there is a combination of the vibration of the string, the strength and type of magnet, the size and type of wire in the coil, all in physical proximity to the string that will create the optimal output from the pickup over the frequency spectrum.
So, does that mean we should rush out and invest in having our guitars connected to an oscilloscope and have every available adjustment made to our guitars? Every pickup height adjusted and every adjustable pole piece specifically moved and tuned to the position that yields the best output according to the scope? Well, um… no. No you shouldn’t because in this case, what appears to be an optimal signal given all of the parameters of inductance will not likely yield what most of us consider to be a “good” tone. Really? If it works for amplifiers, why not guitars? It’s all electronics isn’t it? And optimal is always best, right? Well, um… no. No, they’re not the same and here’s why; in an amplifier, everything in the circuit is active rather than passive and the systematic attempt to control the flow of electrons in the circuit will by physical laws create an optimal point of operation. A pickup on a guitar as we have stated before is a passive device and is completely dependent upon physical proximity to a moving stimulus–in our case, a vibrating string. And the geometry of the guitar, strings, and pickup are respectively so different, and the vibration of the strings so random in nature, as to render an optimally configured and adjusted–a “tuned” system if you will–completely impractical if not impossible.
Part of the problem is that the vertical path of the strings across the pickups is curved while the coils of the pickup are flat. Some compensation in the height of the pole pieces can seek to mimic the curvature of the strings but this, too, can prove problematic in that the magnetic field can be somewhat unbalanced and will result in the generation of unwanted overtones. (a.k.a. “Strat-it is”). So, are you saying that some things about electric guitars can be optimized and others can’t? Yep, that’s exactly what I’m saying. In fact, it is the very “wrongness” of the way pickups can and can’t be adjusted physically and electrically that create the very “rightness” that we’ve become accustomed to hearing. Yes, there was a time when an amp that was turned up to the point of distortion was considered wrong…. Just imagine that. With the vast spectrum of tonality available to the electric guitarist just by varying the amount of distortion they can use, how could that have ever been thought of as wrong? Wrong is right, less is more, soft is loud… It’s a funny old world out here in Guitarland.
Need to know? Just ask… Charlie (firstname.lastname@example.org)