*Image taken from PetrucciForum
How Guitar Tone Is Made: The Principles Of Tone and Sonically Balancing Your Rig.
The pickups: The most important part of the rig
Whether electric or electro-acoustic guitar, the amplified sound starts with the pickups. There are different ways of categorizing pickups: active or passive, single-coil or humbucker, etc…, but basically they all have one thing in common; they are magnetic transducers, ‘reading’ the steel strings of the guitar and creating an electrical signal that can be amplified before going to another transducer, the speaker.
* A transducer is something which can convert one type of energy into another.
The best thing that all of the ‘tools’ between the first and second transducer can do is amplify the signal of the first transducer in such a transparent way that all of it reaches the second transducer; anything else it does is taking away parts of the original signal so that less of it remains to go to the second transducer either by cutting frequencies, by copying parts of the signal and adding them back in altered form, or by over-amplifying the signal so that less of it remains and dynamics are lost. This can sometimes be very much what we want, but still it’s quite clear that everything will sound ‘better’ if the signal coming from the first transducer is of a higher quality, which means that it has more information on dynamics, frequency range, harmonic content, etc…
This is why the pickups are the most important part of the entire rig. Compare it to photo-shopping an image; Photoshop filters always work the same, the quality of the resulting image will mainly depend on the quality of the original picture, how much resolution, colour bandwidth, lighting dynamics etc..
Basically, the better the pickup, the most tone information it transduces.
The performance of a pickup depends on a lot of factors, internal and external.
Internal performance factors:
- The core materials used: Steel and alnico are known for their wide range, balanced way of picking up the sound but alnico core materials will need more coil windings to reach the same inductance. Other materials will have less frequency range and/or less tonal balance.
- The system and level of inductance: Inductance (expressed in Henries) is the principle that converts the magnetic flux variations read out from the strings to electrical energy. Basically, this is done by surrounding the core material with a coil. The size of the coil, the way it is wired (tight or loose), the wire used, etc… are all factors that determine the performance of the pickup in terms of output.
External performance factors:
- There is a plethora of external factors that influence the performance of a pickup: string material and quality, quality of the guitar hardware, quality of the wood (a rich guitar sound from an average guitar is simply impossible, period), the ability of the guitar to let the strings form the sound (high quality really hard and dry wood, light but with superior form stability is a must for a very rich and pure tone), a number of electromagnetic factors (material of guitar hardware, position of the hardware, baseplates of pickups, guitar shielding materials used, strings material, etc…).
Some external factors can be made internal, for instance the superb Samarium Cobalt Noiseless pickups, which are designed by the great Bill Lawrence, who is the one and only man on the planet that really knows all the magnetic influences and uses materials inserted in a certain way between the stacked coils of the noiseless pickups to influence the sound so that these coils sound exactly like, or better than original Fender designs. Everyone that has played the Samarium Cobalt Noiseless pickups knows that these are the best exact Fender sound pickups in existence and also know that they are a lot better than Fender’s own present N3 designs, which are a major downgrade in comparison to the Bill Lawrence design.
- The pickup “load”: This is THE most important external pickup performance factor because whatever the sound the pickup was conceived to produce, it can only do this if it can work at normal specifications level.
The Pickup load
A pickup requires a maximum load to perform optimally. Pickup “load” is also known as pickup “drain.” Basically the output of the pickup cannot be “drained” too fast, or the tone has no chance to form completely. This has everything to do with the “form” of the energy that is generated by the pickup (the coil generates voltage variations), and the “form” of the electrical energy that is required for further amplification, which is named “current”. I will not get into Ohm’s law, but basically the relation between volt (voltage) and ampere (current) is always constant for a certain amount of electrical energy. I won’t get into Fourier analysis either, but the audio signal is basically a complex combination of superimposed waves of variable current. This complete audio signal can be analysed and broken down in, for example, sinus waves (pretty much like the sinus waves of the strings, whereof the vibration in itself is a complex combination of superimposed sinus waves in multiple directions, that is pickup up in only 2D by the pickups, like a cartographic projection of a landscape).
Everyone knows about the relation between pickup load and tone, everyone knows that single coils need 250 kOhm pots and humbuckers need 500 kOhm pots for instance, because otherwise single coils sound too harsh and trebly and humbuckers would sound too dull and muddy. This however has nothing to do with the fact that these are single coils or humbuckers, but with the inductance of the pickups. A pickup with more coil windings and/or stronger core material, will have a higher amount of Henries, which is the unit for inductance. The lower the inductance, the lower the output but the higher the integrity of the audio signal (frequency range and dynamics). Every part that comes after the pickups will act as a filter, taking away parts of the audio signal.
For instance: A cable will have a certain capacitance.
A resistor, capacitor and ground connection is basically what a tone filter is: The signal passes through a resistor, which regulates the amount of resistance to the signal before it runs to ground and is eliminated. A capacitor cuts the frequencies that can run to ground or that are blocked. So, more resistance means less signal running to ground, and less resistance means more signal loss. A good tone control will have a defeat setting which will take the resistor out of the circuit when it is at maximum setting. Most Asian (even expensive) guitars don’t have that feature for instance, and will also have cheaper resistors (potentiometers) that will affect the audio signal more, so less is left over. But even when the guitar has no tone control, there is still the guitar cable with its capacitance, which will act as a tone filter in combination with the tone potentiometer.
Whereas the lower inductance of a single coil pickup keeps the signal clearer when using a higher capacitance cable, this is not the case for pickups with higher inductance.
Conclusion: Low output single coils, when used with the same tone-narrowing circuit, will perform much better than humbuckers because they are lower output pickups. So in order to keep humbuckers, or higher output pickups, in general from losing clarity and definition they have to be run into high value resistors to separate them from ground or indirect ground (tone circuits). That’s why pro players that use high output pickups, basically anything above 8.0-8.5 Henries inductance, will use 1 MOhm pots on their guitars and very short, very high quality (very low capacitance) cable, or maybe a normal length cable but then a 2 MOhm pot for instance. The difference it makes is quite spectacular, much more spectacular than other parts in their rig.
The rest of the rig
By sort of tacit convention, due to the state of technology in the fifties, the input impedance of most amps is set at 1 MOhm. This is pretty much a given. Boutique amp makers will use higher input impedances to allow less pickup drain and therefore a more defined and clear sound.
That’s the input impedance, which is like a fix milestone in the chain, that allows players to balance their rig in order to get the tone they want, not – like the pots on the guitar – by changing the value of the impedance, but rather by knowing that at that point, the input into the amp, the impedance will be 1 MOhm.
Does this mean anything at all? No, it’s at best an application of “better the devil you know than the devil you don’t” or something, BUT, it’s the measure to which everything is measured, IN PARTICULAR the impedance guitars are MADE to meet through a relatively low capacitance maximum 6 meter long guitar cable. It’s also an opportunity for players to adapt the parts of the rig that can compensate for parts they use that screw up the delicate balance. For instance, a player uses a 10 meter long cable and humbuckers… wow, very bad idea, unless he can find a way to restore the balance, for instance by using a 4 MOhm volume pot on his guitar, or by amplifying the high impedance voltage focused signal from the pickups into a low impedance current focused signal before the signal meets the cable. Which is what EMG active pickups do best.
How? By using an op-amp (operational amplifier), which is a small integrated circuit that is typically characterised by a very high input impedance, very low output impedance, and a good signal/noise ratio. An op-amp is a small chip, small enough to fit inside a pickup and can be used in a variety of applications. I love the marketing bullshit of Seymour Duncan (“differential amplification blablah”) that tries to sell the “Blackout module” separately to be used with regular passive pickups. The module is sold for a very high price, for barely being anything more than a decently intelligent package of a standard 0.75 EUR op-amp.
The same exercise in balancing the “drain” is valid for all the parts of the rig that for a long sequence, and that are all hooked to the pickups. It’s not just the first part the pickups “see” that is important, it’s the full sequence of parts that defines the total pickup load, although the first parts are the most influential.
The reality is that every tone control, every sound changing stage, tube or silicon, is basically a filter that aims to lead certain parts of the signal to ground.
Most of the time tone control or amplification level controls are basically passive controls that function pretty much in the same way; a variable resistor that will regulate how difficult it is for the signal to run to ground, entirely or partly.
A volume control for instance at the lowest setting means very low resistance to the signal running to ground completely, a tone control at the lowest setting means very low resistance to the signal running partly to ground. Most controls are passive, which means that less signal is running to ground when the control is cranked.
Ground is the ultimate drain, it drains quickly, it’s like a black hole for electrical signal. Therefore the signal remains most intact when the control is at maximum setting, and more drain to ground enhances the drain on the entire circuit, which means lesser pickup performance. The impact on pickup performance of tone controls on an amp might not be as obvious, but it is still there, and depending on amp design, the impact on pickup performance can be considerable.
Supplementary parts of the rig
A guitar rig often comprises parts that are not really necessary for the normal functioning, but serve a specific purpose, like overdrive/distortion stages in the amp or before the amp, or other effects.
Every effect has controls and/or amplification stages like the amp itself, so the above repeats itself for every part in the signal chain. One single part can cause enough drain to ruin the pickup performance completely.
As stated above, the normal impedance of an amp input is 1 MOhm, and guitars are made to function with that, so the ideal situation would be to mimic this for every part that precedes the amp in the chain. For example: a stomp box ideally would have an input impedance of 1 MOhm and a low output impedance in order to avoid turning what comes behind the stomp box into a tone filter.
But, some of the most loved stomp boxes have a much lower input impedance than that and sometimes a higher output impedance. What to do then?
Most of the time? Nothing at all. A lower input impedance will cause more pickup load, a lower output impedance will cause tone loss after the pedal, but these are in many cases part of the “sound” of that effect. For instance: the added warmth of some boost or overdrive pedals (old Boss OD-1, EHX LPB-1, Ibanez Tubescreamers, etc…) is a result of the treble cut and loss of dynamics that is a direct consequence of the 400-500 kOhm input impedance range. One of these effects can be integrated, and the effect on pickup performance can be wanted by a player, but when several devices cause pickup load, or when the player wants the option to play without this draining effect when the draining effect is off, solutions have to be found.
The most popular solution is the ‘ostrich solution’: to put your head in the sand! This is the true bypass solution. Basically, when the effect is off, the signal is hardwired to go through the pedal. If the effect circuit is run to ground when the effect is true bypassed, as it should, then the impact on the signal will be minimal, and limited to the capacitance it causes. In order to counter the effect of the capacitance the solution is to drive it with a very low impedance signal feed which means that true bypass pedals should be preceded by a buffer that turns the high impedance guitar signal into a low impedance signal.
Any cable length between guitar and amp of more than about 5 m with high quality low capacitance cable and about 1 m with average quality cable, will need a buffer in order to avoid audible tone loss.
So, one single true bypass effect switched off might still be acceptable, maybe two also, if short cables are used, but more than that and the whole chain will act as a tone circuit, unless it is properly buffered.
A buffer is a very simple thing, it’s basically an amplifier circuit that turns the high impedance input signal into a low impedance output signal.
The ideal op-amp would be the ideal solution, infinitely high input impedance, very low output impedance, extremesignal/noise ratio. In reality, these specs cannot be met, but nevertheless, op-amps can really work, and some high end manufacturers use simple op-amp circuits to make buffers (e.g. Brian Wampler), just as they are very popular with mainstream manufacturers because of their very low cost (e.g. Boss, Ibanez) and reliable performance.
Some manufacturers don’t use op-amp chips, but want to use discrete circuitry, and some opt for single ended class A circuitry with discrete field effect transistors (e.g. Radial, Pete Cornish, Bob Bradshaw). Some high end manufacturers use very high impedance to enhance the pickup performance dramatically (e.g. Burkhard Lehle’s Sunday Driver which is a single class A junction field effect transistor based preamp with switchable input impedance between 1 MOhm and 4MOhm).
The difference between all these circuits is, in my opinion, not as enormous as the marketing of these products would want the public to believe. There is a difference, and personally – because it’s not expensive anyway – I like metal oxide semiconductor field effect transistor single ended class A amplifier circuits as buffer, because in critical situations, where an integrated circuit would meet the limits of its specification, a discrete MOS-FET based circuit still performs really well. Better is always possible, but as with everything the last 1 % of quality increase takes a 1000 % of effort increase.
How to use the buffer(s)
This is a matter of taste. Some like a tone that is warmer, which means that they want a certain level of tone loss (or “tone suck”), some like a very pristine and pure guitar sound.
Generally, the first principle in this dissertation still stands; what’s the use of getting a really high end buffer if you’re going to use active pickups or very high output humbuckers… no use at all. With these types of pickups, a simple buffer to counter the tone loss effects of the chain itself is more than enough. So if you have pickups with an inductance of more than 8.5-9 Henries, a simple op-amp type buffer that mimics the behaviour of an amp will do the trick. It doesn’t even have to be a dedicated buffer, a buffered pedal with a good generic buffer will do, for instance a modern Boss pedal, with a typical 1 MOhm input impedance and a low output impedance (50-200 kOhm). Typical candidates for a first pedal in the chain that can do decent buffering: Boss TU-2/3 or Boss FZ-5/ML-2/ST-2.
An alternative is a trick used by many professional: the always-on boutique pedal. Basically a lot of boutique pedals have a very simple straight-forward circuit with high quality parts, and an input impedance of 1 MOhm or more and a very low output impedance. When they are left always on they have a positive effect on the pickup performance, and therefore make the guitar sound more pristine, detailed and defined. The preamp circuitry of the effect pedal, while adding the effect, also provides the buffering to counter the tone loss of the chain.
Asian guitars, that have much lower wood quality than premium US builds, will generally, because of the construction tolerance and the lower wood quality (even if they “look” very good), have much less potential for complete tone formation than premium US builds. So even with lower output pickups, maximising the pickup performance will not make a hell of a lot of difference.
However, with a quality guitar with good low to moderate output pickups, for instance an American Standard Fender Stratocaster or Telecaster or a high quality clone thereof (e.g. Tom Anderson Guitar Works, John Suhr, Washburn USA Custom Shop, Tyler, Schecter Custom Shop, and an endless list of smaller manufacturers of handmade strat and tele clones), with an inductance of 2.4 to about 6 Henries, maximising the pickup performance will make a huge difference. Running a strat into a 4 to 10 MOhm impedance buffer really brings the liveliness of the guitar up and gives it a marvellous acoustic quality whereby every material in the guitar can be heard and every expressive detail in the playing comes through loud and clear. Quite spectacular what a good buffer can do in those cases!
To get the most tone from a guitar, the most important elements have to be secured: the acoustic quality of the guitar and the quality of the pickups. Then the pickup performance has to be maximised by impedance matching the rest of the rig so that the largest possible portion of the original signal can be delivered to the final transducer, the speaker, which confides the signal back to the air, and thus to the ear.
However, almost every guitarist wants a certain amount of tone loss and the trick is to be able to control the exact amount and know what part of the signal chain is responsible for that: hotter pickups, cable length, true bypass effects, low input impedance circuitry, tone/gain/channel volume settings on the amp, etc…
Everyone has his / her own system of balancing the tone of the rig and there is nothing more personal. I use a colour code labelling system for all parts of the chain myself which allows me to balance the tone loss of the complete chain in a glance, and I set the amp controls to match the performance of the entire rig rather than to try to force the amp into sounds that I would like to have but that ruin the guitar pickups’ performance. I’d rather take another amp or guitar in that case!