Owner`s manual

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Gain, Level, Sensitivity, and Power Relationships
Another source of error is the interrelationship between gain, signal level, sensitivity, and output
power. First some definitions:
Gain Generally this is shorthand for voltage gain. A measure of the amplification factor
of an amplifier, or the output voltage divided by the input voltage. Thus, 10 volts
out for 1 volt in is a gain of 10. Sometimes gain figures are converted into decibels
(dB). In this case, a voltage gain of 10 converts to a voltage gain of 20 dB. It’s
handy to use decibels for gain calculations because the only math you need is
simple addition and subtraction (once you do the decibel conversion).
Signal Level This is the strength of a signal, measured in volts. Again, sometimes signal levels
are measured in decibels, which states them as a ratio of two quantities: the signal,
and a known reference level. Signal levels are also referred to by their ability to
drive an input: line level, speaker level. While the voltage present may be the
same, the current (amperage) capability may not be the same. Basically, this is
what is different between a 1 volt line level signal and a 1 volt speaker level
signal.
Sensitivity This is a measure of the input signal requirement of a device for some stated
output level. Sensitivity is intimately related to gain. If an amplifier has a gain of
10, and it’s rated output level is 10 volts, then it’s sensitivity is stated as 1 volt.
It’s important to remember that low sensitivity means a higher voltage is necessary
to drive the unit, while high sensitivity means less voltage is required. Note that
sensitivity has nothing to do with power output.
Power Output Power represents energy, which can do work (like moving a loudspeaker cone).
Power is always measured in watts. Power has nothing directly in common with
sensitivity. It is equally possible to have an amplifier that has low sensitivity, but
high power output as well as one that has high sensitivity, but low power output.
The old volume control myth
A common old wives tale is the belief that the percentage rotation of the volume control represents
the same percentage of output power. Here’s the way it goes: “I’ve got so much power that I only
need to turn up the volume to 10 o’clock (20% rotation)”. Since the volume control generally
adjusts the overall gain of the system, there is one unique signal level where wide open (100%
rotation) represents full power output from the power amplifier. Since most volume controls are
followed by gain (to make interfacing varied signal sources easier), the average system reaches full
power long before 100% rotation is reached. Thus, the amount of volume control rotation required
to drive the system to full output depends on:
1. The signal level present at the input of the volume control.
2. The amount of gain following the volume control.
3. The sensitivity of the power amplifier (better low than high, from a noise standpoint).
Why bother? A good reason is to make sure that the signal going to the power amplifier is as
strong as possible. This helps to subjectively reduce noise that may be induced between the head
unit and the power amplifier by making the signal in the cable much stronger than the induced
noise.
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