Simple Guide to DIY Electronics #1: Passive Components August 16, 2011 16:31

Electronic components are called 'passive' when they don't produce gain or require a power supply to function. While there are numerous components that meet this definition, when we refer to 'passive components' we usually mean the following three types: resistors, diodes, and capacitors.


Resistors are those little, candy-looking tubes that populate almost every audio project in great numbers. Their job is to present a certain amount of opposition, or resistance, to the electrical current flowing through them. There are three specifications you'll use to identify the correct resistor for a certain job:
  • Resistance: The amount of resistance, measured in in Ohms (Ω). This is usually indicated on the surface of the resistor with color-coded stripes.
  • Tolerance: The degree of precision to which the resistor was manufactured. For example, a 1k resistor manufactured to ±1% tolerance may have an actual value between 990 and 1.1k ohms. This is also typically indicated with a color-coded stripe.
  • Power: The maximum power (heat) a resistor can dissipate without being damaged. This is not specified on the body of most resistors, but can often be guessed from the resistor's physical size with a little experience. Most resistors in audio circuits dissipate less than 1/2 Watt of power.
  • Resistive Material: Resistors are made from a wide range of materials, but the most common in audio circuits are:
    • metal film resistorMetal Film: By far the most common in modern equipment. They are nearly transparent in audio circuits and can be made cheaply to very strict tolerances.
    • carbon comp resistorCarbon Composition: Long since surpassed by film resistors in terms of noise and precision, carbon comps are nonetheless still used, especially in circuits that attempt to clone a vintage unit. Many vintage guitar pedal enthusiasts, for example, use exclusively carbon comps.
    • carbon film resistorCarbon Film: Precise and low-noise enough for most audio applications. Often used when a certain value or power rating is not available in metal film.


Capacitors ("caps" for short) are the second most common component in audio projects. They are designed to store and discharge a certain amount of energy and play a wide range of roles in circuits, from smoothing power to filtering frequencies from an audio signal. There are three important specs that define a capacitor:
  • Capactiance: The amount of capacitance, measured in farads. Common subdivisions of the farad are micro-farads (uF) nano-farads (nF) and pico-farads (pF).
  • Voltage: The maximum operating voltage.
  • Polarity: Some capacitors are polarized and must be installed a certain way in order to remain in their "unexploded" state :O If a capacitor is polarized, its polarity will be marked on the body of the capacitor and accordingly on the schematic or PCB in which it is used.
Capacitors come in a huge variety. The following are the most often encountered in audio DIY:
  • metal film resistorCeramic: Small, non-polarized, usually used as bypass caps.
  • electrolytic capacitorElectrolytic: Capable of high capacitance per volume, usually polarized.
  • mica capacitorSilver Mica: Linear and stable, but relatively large and expensive.
  • polyester capacitorPolyester: Low tolerance and low voltage, often seen in audio circuits.
  • polystyrene capacitorPolystyrene: High stability, low distortion.


Diodes are components that allow current to flow through them in only one direction. A diode's two leads, the anode and the cathode, will usually be labeled and must be installed correctly in order for the diode to work properly. Common types of diodes found in audio projects are:
  • LEDLight Emitting Diode: Emits light when current passes through it. The anode is indicated by having a longer lead than the cathode.
  • schottky diodeSchottky Diode: Designed to cause as little voltage drop as possible. The cathode is usually marked with a silver stripe on the diode's body.
  • zener diodeZener Diode: Operates like a standard diode until a certain voltage is reached, when it allows current to flow both ways. The cathode is usually marked with a stripe.
Further Reading:.