TRC DIY #1 – Getting Started with Audio Electronics
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The world of analogue audio is intrinsically linked with electronics engineering. Audiophiles and musicians alike swear by their favourite equipment, but few dare to delve into the seemingly mysterious world of the circuit board and fully commander their electric signals from source to the loudspeaker.
In this series, we will dip our feet into the basics of audio electronics to better understand, and even build our own amplifiers, sound systems, synthesisers and more. Let’s start with some core concepts needed to build our own circuits, from kits, or from scratch!
1. Voltage, Current, and Power:
Voltage refers to the potential or pressure of electricity and is measured in volts; while current refers to the actual flow of electrons and is measured in amperes. The product of voltage and current is the power used in a device and is measured in watts. Audio signals change direction based on their frequency and are thus considered AC or alternating currents.
2. Resistors and Resistance:
Resistors oppose current flow and are used to limit current or divide voltage. The larger the resistor, the less will be the current flow through it and the larger the voltage “dropped” over it. Resisters may be connected in series or parallel.
In the former case, the total opposition to current flow will be increased and voltage will divide proportionally across each resistance, while in the latter case, opposition to current flow decreases and the voltage across each “branch” is the same.
Resistors are marked with a colour code giving their value in ohms (Ω), and being able to read their value is essential to building electronics kits. Fortunately, you can just refer to the graph shown below.
3. Capacitors and Capacitance:
Capacitors, earlier known as condensers, allow AC signals to pass while blocking direct current (DC). Thus, they are used to couple signals between circuits or filter certain frequencies. Capacitance is measured in farads. Higher values allow more low frequencies to pass, while smaller values block them.
“Electrolytic” capacitors have negative and positive sides, and thus must be connected correctly in a circuit. While ceramic or film capacitors are unpolarised.
Electrolytics have their value written in microfarads(µF) and the negative side marked with a line, while ceramics usually use a three-digit code in which the last number represents the number of zeros to be added for a value in picofarads.
4. Tubes and Transistors:
Vacuum tubes and transistors are three-terminal devices that can amplify a small signal. For example, in a triode tube, a small signal between the grid and cathode pins can control a large current between the cathode and anode pins.
A bipolar-junction transistor works in a similar fashion and its respective pins are known as base, emitter, and collector. This principle allows your amplifier to step up the very tiny signal from your turntable’s cartridge enough to drive your loudspeakers through basically a chain of transistors.
An Integrated Circuit (IC) contains numerous transistors arranged for a particular purpose such as amplification of an audio signal or maybe even generating an audio signal. In the next part of this series, we will put all this knowledge together by building an IC based audio-amplifier kit.
Written by: Santaji Shirke ( @_electroidiot )
