AudioControl SA-3052A, Руководство по эксплуатации

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SA-3052A Owner’s Manual
6-6
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Chapter 6 - Getting the Last ¼ dB
Gain, Level, Sensitivity, and Power Relationships
Another source of error is the interrelationship between gain, signal level, sensitivi-
ty, and output power. First some definitions:
GAIN
Generally this is shorthand for voltage gain. A measure of the am-
plification 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 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, some-
times 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, etc. 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 sig-
nal 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 re-
quired. Note that sensitivity has nothing to do with power output.
POWER OUTPUT
Power represents energy, which can do work (like moving a loud-
speaker 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 out -
put as well as one that has high sensitivity, but low power output.
For example, let’s take a system where we have a power amplifier that has relatively
low sensitivity (1.5 volts for full output). We’ll hook this up to a head unit that has a rat-
ed output of 0.25 volts. What is the end result? Chances are that the system won’t ever
realize the full potential of the power amplifier. Why? Because the head unit is giving up
the ghost long before its output has reached the level required by the power amplifier for
full output. What is needed here is an amplifier with higher sensitivity.
Now, let’s take an amplifier that has adjustable gain. Remember that gain and input
sensitivity are intimately related...high gain means high input sensitivity (lower voltage
required for full output) while low gain means low input sensitivity (higher voltage re-
quired for full output). We’ll hook this up to an amplified (capable of delivering 4 watts
into 4 ohms) receiver. Assume that the receiver is a bit marginal in the residual noise
department. If you want to get as much out of this setup as possible, then you’re going to
have to find the right relationship between the gains of the two components.