Too Many Knobs…
Hello folks. This article is inspired by a question from channel member Dave E. who wrote in to ask about which of the myriad knobs in his signal chain was most important and which ones to use as so many are called exactly the same thing. A really excellent question, and Dave is not alone in wondering this. Many musicians have not considered this and may not be getting the tone that they actually want. Thus I will take you on a somewhat deep dive and then you can decide for yourself which knobs to use and which you choose to set and forget, if any or all. Dave’s question applied specifically to acoustic guitars with pickups, having either internal or external pickups so I will address that specifically but also cover electric guitars and electric basses. I will also try to address the further scope of active pickups in its own section.
Passive Systems
A passive system has no power system to drive parametric like EQ systems in instruments and does not include pickups with selectable voicings such as we would find in something like the Fishman Fluence family. To be clear, any guitar that uses a piezoelectric pickup requires a preamp of some kind that requires power making it an active pickup.
The volume control on your guitar or gain control on an external preamp or in the input stage on an amplifier is a potentiometer. Volume controls only reduce signal from full on, they do not increase signal, so if you want to hear everything that the device is putting out, you turn the volume up all the way. Some potentiometers even have a click position that takes the potentiometer out of the circuit entirely. This is like a tone control but considerably less complicated.
Let’s move to the tone potentiometer in a typical passive arrangement. As you know, in the applications in instrument pickups, external pickup preamps and the tone controls in an amplifier, the potentiometer acts as a variable resistor. Theoretically when fully clockwise, the control has no impact on the sound at all. In a tone pot, as the control is rotated counter clockwise, attenuation of the treble frequencies occur based on the value of the capacitor connected to the tone control. Thus tone controls don’t add anything, they only take away.
There are two fundamental potentiometer designs. A linear potentiometer rolls off signal linearly. This is ideal when each position must be a fixed change between the prior and the next position. This is an excellent choice where you want a consistent fall off in output, such as in a lighting dimmer or an output volume control like a master volume. An audio taper potentiometer follows a logarithmic path, so each “notch” is not an equal (linear) change. Audio taper potentiometers more closely mimic how the human ear and brain interpret changes. Use of a linear potentiometer as a tone control results in very rapid treble attenuation and in better designs, only audio taper potentiometers are used for tone controls. The value of the capacitor also has impact. This higher the capacitor rating, the more treble attenuation happens. Some guitars are available without any tone potentiometers at all.
When we come to the external preamp, if there is one tone control only, it does the same thing. If there are more than one tone controls, the signal gets split to each of them where each tone control has a cutoff frequency where it is effective or a pair of cutoff frequencies as we would find in a tone control marked midrange.
An external preamp is often a powered device. It does potentially several things. The first is to boost the signal from a relatively weak output pickup such as a piezo design. The second is to do impedance matching from the preamp output to the amplifier input (which is in fact, another preamplifier). Then comes the tone stack. The more bands offered, the more frequency shaping happens at the guitar before the signal reaches the amplifier or in the case of a DI connection, the preamplifier in the interface or the sound board in a studio. If an external preamp has a tone stack, it provides some colouration to the frequency response simply by being present. All preamps have some impact on the signal, although some can be cleaner (less colour) than others. The preamps built within most piezo systems are very clean, and this is way the unprocessed tone of most piezos is so irritating. Another function could be a notch filter, used to control feedback in an acoustic electric guitar. This is basically a variable filter that cuts out a specific frequency where feedback can occur. Most acoustic amplifiers will have this as well and all studio systems will have this capability in some way or another. The preamp may also add an additional volume control into the circuit. Finally a preamp could offer a balanced line output that allows for longer capable lengths and DI (direct injection) to a studio board or interface. Some preamps offer the DI to be selectable to be pre or post tone stack.
When we do get our signal to our amplifier we hit another preamp. Its purpose is to raise the level of the input signal to a usable level. Stacking a number of gain controls (labeled volume most often) is how an amplifier can be driven to harmonic distortion by overdriving the input of the guitar preamplifier. This is, at a very basic level what boosts, and overdrives do. Distortions and Fuzzes aggressively colour the signal in addition to providing a boost. The amplifier tone stack is the same as in a preamplifier built into a guitar or in an external preamp. It splits the signal into frequency bands using a combination of high pass and low pass filters to a series a potentiometers, which in better amps are always audio taper designs. At full, the potentiometer has no effect and as we roll it off, the resistance in the potentiometer increases, cutting whatever frequencies are in the signal that the potentiometer engages. Again, there is no boost applied to a band, only the application or removal of resistance in the band. A common misunderstanding, that we see particularly on high output amps is to dial everything up to ten or twelve or whatever. This just means that the potentiometers are providing no resistance at all, at least in theory.
Active Pickups
Active Pickup designs use the same design concepts as passive pickups but typically have a very low output level and thus include an in instrument preamplifier to boost the signal strength. These preamplifiers will also do some impedance lowering in some cases to increase cable run lengths. Active pickup types include the aforementioned piezo electric type, or some electric guitar pickups like some EMG offerings or the Fishman Fluence line which require the presence of power to run the built in preamplifier. Most active pickups have a volume control and a general purpose tone control, but many basses come from the factory with active pickups and active EQ systems. These models often allow for a passive mode and an active mode. The active mode may increase the output a bit but more often replaces the general use single tone control with multiple tone controls for bass, middle and treble and can also offer selections for the centre frequency for each of these controls. Think of a simple 3 band Parametric equalizer. This is valuable as more bass recordings go direct to desk or through a speaker simulator to the desk bypassing a traditional preamplifier / amplifier entirely. By putting the parametric eq in the player’s fingers, all the control goes there. Again though if you run the control wide open, the effect on the sound from the pickup should be minimal to nothing at all. In other respects, active pickups are the same as passive pickups, albeit with the requirement for power. In most cases, dead battery or batteries means no sound at all.
Passive or Active
How many nanobots are in your ear right now? Yeah, I don’t know either. The pickup world is filled with options, using different magnet types, different wire types, different bobbin shapes, different contact methods and all manner of other stuff that is mostly marketing fluff. Pickups are not magic. There is no powdered unicorn horn or a secret squirrel kind of magnet that no other company can make, or a special kind of wire that was only ever made once and that one spool got hidden in a drawer in a desk in a collapsed basement in Akron, that makes a pickup uncopyable. All that is complete horseshit. Pick the pickup(s) that sound good to you and deliver the kind of tone that you are looking for. A lot of players prefer passive systems so they are not on a leash to a battery or batteries that could leave them dead in the water with minimal notice. Other players like the ability for a pickup to have unique voices or to have that parametric EQ on their bass for full tone sculpting. If you are talking about an acoustic instrument, piezos are always active. However, there are acoustic pickups that are based on contact condenser microphones and even condenser mikes on a gooseneck inside the guitar body. Those types of pickups don’t need batteries of any kind, but may perform better with long cables by use of an external preamp, which is going to have to have some kind of power source. You do you and forget the rest of the miasma of crapola. I have instruments with both passive and active pickups. Both work fine, although I would like to take the designers of some battery boxes for active pickups out to the woodshed for an axe lesson. If I cannot change the battery or batteries in an active instrument in less than a minute, the design of battery access simultaneously sucks and blows, and if a screwdriver is required, it should be shoved into the eye socket of the designer. Just saying.
So Is There A Best Route?
All this leads to the question of too many knobs, aka option paralysis. There is no yes or no generic answer as to which potentiometers to use. The quality of the potentiometer, the build type and accuracy of the capacitors, the high and low pass filters and other elements in the circuit all contribute to the final sound. Some players run the instrument preamps, whether internal or external up to full and use the amp controls. Others run the amp tone stack wide open and only use the instrument controls. Most use a combination of both, finding a comfortable generic sound with the amp settings, and the instrument controls wide open, and then use the instrument controls as subtle controllers for the before amp signal.. To find what is optimal for your own use, you should try them all and find a model that suits you the best.
Some studio engineers and producers want the instrument controls wide open, which in theory and in actual practice gives them the widest latitude for signal modification using the studio grade gear that they have. This really only works when the instrument goes direct to desk. A microphone adds colour. When you mic an amplifier it adds colour, when you mic an acoustic guitar the mic adds colour. So too do the board preamps even before the signal hits any equalization or compression tools. The only truly clean signal doesn’t actually exist, so don’t worry.
Thanks as always for reading and supporting the channel. Please post a comment or send in a question like Dave did. I read and respond to all, and I’m really glad when a question results in an article or podcast episode. For That Guitar Lover, I’m Ross Chevalier and until next time, peace.
