A stereo system is based on a SOURCE, AMPLIFIER and SPEAKERS. Types of sources are - turntable, c.d player, tuner and tape recorder. Each source is connected to the amplifier and the amplifier drives the speakers.
Although most of us have an amplifier in one box, and many of us have a full stereo in one box ("Mini systems"), stereo system is built of two "twins" paths from source to speakers. The c.d for example, has two digital data on it - one for the left channel and the other for the right channel. The c.d player reads the data for the left channel and moves it to a system that translates the digital data to analogue - then to a first amplification unit.
At the same time, the c.d player reads the right channel data from c.d, moves it to ANOTHER translate unit and first amplification - and this RIGHT unit is IDENTICAL to LEFT unit.
The amplifier, is built of TWO identical paths - each is a MONO amplifier.
C.d player feeds the left channel and right channel of the amplifier via separate cords - and each path of amplification works independently to amplify the data and to feed the speaker - right amplification path feeds the right speaker and left amplification path feeds the left speaker.
So - every stereo system is built of two mono paths from source to speaker.
We can see it at the basic schema above. Every source has two outputs - one for left channel and the second for right channel (Tape recorder has also two inputs - to record from amplifier, inputs to left and right channels). The outputs of the source connected to inputs of the amplifier. All sources but the turntable, are connected to the Source (Input) Selector. The data from turntable has additional circuit - RIAA we'll discuss it later. The source selector connects one selected source to the PRE AMPLIFIERS inputs - one pre amp takes the left channel and the second takes the right. Volume and balance knobs control the level of input data. Although usually INPUT SELECTOR and VOLUME control are one knob each, inside the amplifier each is built of two parts - INPUT SELECTOR for RIGHT channel and INPUT SELECTOR for LEFT channel. VOLUME for LEFT channel and VOLUME for RIGHT channel. It is important to see, that each KNOB we add to amplifier - is consists of TWO identical parts - for left and right channels.
If we add bass and treble knobs, we add FOUR more parts to our amplifier. So what ?
When we discussed STEREO HEARING, we discussed an example when one singer plays a guitar. While recording, the engineer records guitar and singer on both channels exactly the same. When we play this c.d, the amplifier gets two identical inputs to left and right channels. In order to get the right IMAGE when listening, we need that each speaker of our system will give us exactly the same sounds and levels as the other, exactly at the same time (we discussed how fast is our hearing system) otherwise we will lose the FOCUS of IMAGE. In order to give our amplifier the ability to amplify both channels exactly the same, we need as short as possible an ELECTRICAL PATH from input to output. Adding unneeded Knobs destroy the path and destroy the balance of paths - because each knob has two parts that must work exactly the same at right and left channels. Because of this reason, many amplifiers have only INPUT SELECTOR, VOLUME and BALANCE knobs - to assure as short as possible electrical path.
An other very important part in the amplifier is the power supply. This unit powers FOUR main parts - LEFT pre amp. , RIGHT pre amp., LEFT power amp. and RIGHT power amp.
It's a must that this power will feed each of the above without influence from one other.
First we have to understand that pre amp deals with very low level signal. (Around 5 milli volts). Power amp. deals with levels thousands times higher. It happens that one power amp. needs a sudden power from the power supply - we cannot afford this power to disturb the work on pre amps or in the second power amp. Each pre amp and power amp has to work all time independently and with the best conditions.
If something disturbs the work in one part of the amplifier, we loose the IMAGE and FOCUS immediately.
As we see, the quality of sound depends on the the whole
system and not mainly on speakers - as many people think.