This page explains some common basic properties in audio electronics. If any electronic engineers among the readers should find errors here, please let me know so that I don't spread misunderstandings.
* Some equipment may have the polarities switched, so that +/Hot/Send is on pin 3. Sometimes the -/Cold/Return pin is shorted to ground, in which case the signal is no longer balanced.
** Some MIDI boards have jacks for 7- or 8-pin DIN plugs, were the additional pins are for phantom-powering. A 5-pin plug can still be used if you don't care about the phantom power feature.
*** Applies to phantom powered cables only. Actual wiring and voltages differ between manufacturers.
This table is over-simplified and only intended as an orientation. Most components have many more important values, and come in many varieties and qualities for different applications. Component values are usually indicated with color- or number codes, making reference litterature indispensable. For explanation of the electric terms se below.
Name
Function
Applications
Important property units
Resistor
Decrease current flow
Everywhere
Resistance (Ohm), max power (W), tolerance (%)
Potentiometer, "pot" (see section below)
Variable resistor
Guitar and amp controls, volume- and expression pedals
Resistance (Ohm), max power (W), taper (Lin or Log), lifetime (cycles). See also text below.
Capacitor
Store energy, block DC current
Everywhere; power supplies, filter and time circuits
Capacitance (F), AC or only DC current, max voltage (V), tolerance (%)
Coil
Create magnetic fields
Speakers, guitar pickups, relays, electric motors
Inductance (H), max current (A)
Diode
Block current from one direction
Everywhere; rectifier (AC to DC) circuits, abused to create distortion effects
Max voltage (V), max current (A)
Transistor
Amplification
Solid state amp circuits, abused to create distortion effects
Amplification ratio (hFE), polarity (NPN, PNP), max voltage (V), current (A), power (W)
Potentiometers
A potentiometer works like a variable resistor. Potentiometers for sale by electronic part suppliers come in a lot of qualities and varieties:
A potentiometer for use with guitars or pedals should have a long working life, but will of course cost a little more because of this. You can destroy a cheap pot by turning it too fast (like when a guitar volume used for volume swells). Potentiometers tend to oxidize after some time, causing noises when turned. A dirty or oxidized pot can be temporarily cured with contact spray and by turning it back and forth a few times.
The potentiometers effect rating (specified in Watts, symbol: W) will also increase the price but should not matter here since microphone or line level audio signals are so weak (if you'd use the potentiometer to limit speaker level signals it would be a different story).
The impedance (alternating current resistance) indicates how much the pot will dampen the signal and is measured in Ohms (symbol: greek letter Omega, Ω). The damping may also be affected by the impedance of the guitar pickup (not sure about the details).
Since a little signal will always leak to ground through the pot, higher potentiometer impedance values will give you higher max level (a low impedance value means that a larger portion of the signal will leak to ground, even in the potentiometer's max position. You get the strongest signal in a guitar without any volume potentiometer at all.
Together with passive humbucker pickups, a 500 kOhm is a common value for the potentiometer, while passive single-coils use 250 kOhm. Active pickups (like EMG) use only 25 kOhm.
The impedance varies with the signal's frequency. That's what happens when you turn down the level potentiometer on a guitar and the treble decreases at the same time. Because of this a high impedance potentiometer (say 1 MOhm) may give you a more trebly signal from the guitar.
It seems to me (I might be wrong here) that high impedance values will also affect a potentiometer's taper (see below), since a small movement will increase the impedance a lot. For example, if you turn down a high impedance potentiometer just a little the volume will drop drastically.
In an expression pedal the impedance should match that of the effect processor's expression pedal jack, otherwise the resolution may decrease, resulting in an uneven response, or you might encounter other unexpected behaviour.
The taper is the pot's response curve.
Some (all?) expression pedals use linear (lin) taper potentiometers, that will increase the impedance in direct proportion to the potentiometer's movement (that is, in middle position the impedance is increased by half). If you feel that the response of your expression pedal is too abrupt, and you can't adjust it with the G-Force's calibrating curves, you could try changing the potentiometer in the expression pedal into a similar model with a logarithmic instead of linear taper.
Volume knobs and -pedals normally use logarithmic (log) taper pots that will increase the impedance in a cumulative way, where most of the action will happen at one end of the potentiometer's movement. Humans perceive sound levels in a logarithmic way, hence their use in volume pedals. logarithmic pots are usually made simply by dividing the pot into three sections, each with a different impedance. There are also so-called "audio-taper" potentiometers available, designed specifically for audio use. These should be similar to logarithmic ones.
This is a very brief (and simplified) explanation of basic electrical concepts. For a more detailed account check out some decent beginner's book on electronics. A few of the subjects are quite advanced (such as reactance and TRMS) but I'll mention them briefly anyway, since they are important in audio electronics.
Voltage, current, resistance, power
Voltage, current and resistance are related to how electrons behave. Electrons repel each other, so if they are in surplus (or shortage) in one location they'll try to cure this by flowing towards places with relative shortage of electrons (or away from surplus). The intensity of this urge to spread out across the world is called voltage and is measured in Volts, V. The actual movement is called current and is measured in Amperes, A. Since we are dealing with differences in the amount of electrons between two locations, it follows that a voltage can only appear between two locations as well (compare with how a debt must occur between two individuals --you can't be in debt to yourself). Usually a more or less arbitrary reference point is chosen for the voltage, such as "circuit common" or "ground".
Resistance is the quality that stops electrons from flowing, and is measured in Ohms, (symbol: greek letter Omega, Ω). A resistor is an electronic component built especially for this purpose. If the resistance is infinite (such as in isolating materials) no electrons will move at all, and the voltage will remain as it is indefinately. If the resistance is less than infinite, a current will flow in order to even out any electron surplus/shortage. The lower the resistance, the faster this will happen and the warmer the material the current is flowing through will become. If the resistance is high current may still flow provided that the voltage is very high too: even an isolating material such as air (that has very high resistance) will conduct electricity during a thunderstorm, since lightning bolts feature such immense voltages. As the electron flow gradually reaches its new equilibrium, the voltage and current will reflect this and drop to zero.
Voltage, current and resistance are related to each other like this: Voltage = Resistance × Current (or U=RI as it's often written). In other words, if you know two of these values you can calculate the third.
Direct and alternating current
In the example above the electrons moved in just one direction, from surplus to shortage. This is called direct current (DC), and is what you get when "static electricity" discharges, during a thunderstorm or from a battery. However in many man-made situations (such as the signal from an electric guitar) the current's direction will oscillate back and forth. This is called alternating current (AC). The number of times per second something changes direction is called the frequency, and is measured in Herz, Hz. The current from a mains supply normally alternates as a sine wave, with a fixed frequency of 50Hz in most of Western Europe and 60Hz in the USA.
RMS, peak and TRMS values
In every AC cycle the voltage (or current) will first increase from zero to its peak value, then decrease to zero again, change direction and repeat the whole cycle in the opposite direction. The peak value is only reached for two short moments (one positive and one negative) during each AC cycle, just like the zero value (when the direction is changed). Because of these ever-changing voltage/current values an average "root mean square" (RMS) value is used, which is about 0.707 of the peak value. When the domestic mains voltage is said to be 230V (Europe) or 115V (USA) it's the RMS value that is referred to. The actual peak value of 230VRMS is 230 × 1.404 = 323VPeak.
Note that these figures assume that the AC voltage/current is a perfect sine wave. If the wave shape has been deformed by an inductive or capacitive load the above simple formula no longer applies. Some expensive multimeters can still measure it, though. The result is called True Root Mean Square, TRMS.
In the case of audio signals, RMS values become a complicated issue since audio frequencies change all the time.
Power consumtion
When electric current is flowing, power is produced. Usually most of this is wasted as heat, but it can also be put to other uses, such as making a speaker cone move and produce sound. Power is measured in Watts (W), and is calculated by multiplying the voltage drop with the current flow: P = U × I (as it's usually written).
Power produced by an AC current will also be indicated with an RMS value, but in the case of audio amps I'm not sure what this actually means since it's frequency dependent. There's also a difference between continous and peak RMS power: the former is the normal effect produced by the amplifier, the latter is only produced during short moments. Finally, the effect rating of an amp will depend on its impedance. Lower impedance values mean higher effect ratings (since a low-impedance speaker is easier to drive it means the effect increases), but if this is mirrored in the actual sound effect (the speaker's loudness) I don't know.
In all electrical devices a lot of the power that is consumed will be lost as heat. An amp that consumes 50W may give off most of it as heat and only a few watts to drive the speaker.
Above I mentioned resistance to direct currents. Alternating currents react the same way when flowing through a resistive material, but in some cases alternating currents will behave in a more complex fashion.
When direct current flows into a capacitor (an electronic component; almost like a tiny accumulator) it will soon be opposed as the capacitor becomes charged. But since an alternating current moves back and forth it will continously charge and discharge the capacitor and the current's movement will not be completely stopped by it (even if the capacitor blocks the current path, the AC current movement will still continue on the far side of the capacitor, similar to how a wall may prevent airflow but still let through sound waves to the other side). The higher the AC frequency, the less it will be hindered by the capacitor (because the capacitor becomes less charged and therefore less resistive during a fast AC cycle). But the lower the frequency, the more the capacitor will oppose the current (because it becomes more charged during a slower AC cycle). This frequency dependency is called capacitive reactance, XC .
When direct current begins flowing into a coil, a magnetic field is created. The field opposes the current only while it's building up, not after it has reached its max strength. Coils oppose AC currents, since the magnetic field collapses and must be rebuilt every time the current changes direction. Unlike capacitors, the higher the AC frequency, the more the coil opposes the current. This kind of resistance is called inductive reactance, XL .
Impedance, Z, is another word for AC resistance and is made up of the DC resistance together with the capacitive and inductive reactance of a circuit. Unit: Ohm (symbol: greek letter Omega, Ω) just like ordinary resistance. Since audio signals consist of an AC current with varying frequency, and pickups and speakers are made up of coils impedance becomes an important issue.
Impedance of more than one speaker
When two speakers are connected in series, their individual impedances will simply be added together. When connected in parallel, the speaker impedances will decrease according to slightly more complicated formula. As a rule of thumb the total impedance is always bigger than that of the individual speakers' when connected in series, but always less than when the speakers are connected in parallel.
Formula for calculating the impedance of several speakers in series
Formula for calculating the impedance of several parallel speakers
Several speakers connected in both series and parallel
If you connect some speakers in series and some in parallel you must calculate each group separately:
