I prepared this for my son, and he suggested a series of blog posts, so here it is. This information is designed to understand the signal flow and signal levels inside of a stereo receiver, or a sound system with multiple components. This is for consumer retail stereo. There are different electrical standards for Pro Audio–which is sound systems for recording studios or live performance.
For working with consumer stereo, here are some essential concepts to memorize and understand. In subsequent posts, I will talk about signal routing.
Turntable output–output of a coil that detects the movement of a magnet attached to the needle. Its in the millivolt range. Some audiophiles use a moving coil needle where the magnet is stationary. These have a much lower output and we are not using these. If a pre-amp has inputs for both moving coil and moving magnet, the moving magnet input is the correct one unless you know your device is moving coil.
Consumer audio Line Level (the standard for things that have RCA sockets and cables). It is described as (-10 dBV) which translates to full signal as .316 volts peak to peak.
Pro audio (typically balanced cables between equipment used in recording studios or for band live performances). +4 dBV. Note a different unit of measurement is used here. This just reflects that pro audio was entirely distinct to consumer audio and has different standards. +4 dBV translates into .775 volts peak to peak for maximum signal. It is possible to drive pro audio gear with consumer signal levels. One does need to understand how to get the unbalanced -10 DBV signal connected to the balanced pro audio signal. This is a discussion for another day.
Consumer audio -10 DBV–Line level is the standard for the outputs of pre-amps and the inputs to power amps in consumer stereo.
A pre-amp is something that has an input that is less than line level For example, phono for consumer audio and microphone preamps for pro audio.
Signal to power speakers: A signal that has enough voltage and current to drive an 8 ohm speaker to the designated volume level.
Power amp: Takes line level input and puts out speaker power output.
The home stereo receiver has all of these components in one chassis, and the routing of line level signals from the pre-amp to power amp, or from a line level input like CD to the power amp are performed by multi-position selector switches. There is typically a switch that controls which input is sent to the power amp, and another switch that selects the source of a signal sent to the Line Output rca sockets in the back of the stereo.
Consumer stereos often have controls to change relative strengths of different frequency bands–typically treble, and bass. There is also a “loudness” control. It provides a bass boost to compensate for the human ear’s loss of ability to hear bass at lower volumes. (See Fletcher Munson curves) These can be thought of as equalizers that take line level in and emit line level.
The first goal should be to memorize the voltage for consumer line level–.316 volt and that its called -10 DBV. Second, understand what a pre-amp does and what a power amp does. Some people build their sound system with components typically with the pre-amp and power amp in separate chassis, connected by the standard -10 DBV RCA cables.
Next post will cover the subject of signal routing using the rotary switches.