Power Amplifier Sensitivity Table
By Rick Chin
	
One late night, while listening to a band's monitor system, 
one of the band members remarked that they had picked their 
monitor amplifier assignments according to the particular 
sound quality that they found pleasing. That of and by itself 
was not terribly surprising, but that the monitor speakers were 
the same model and that the amplifiers were not made me wonder 
if they were really hearing the sensitivity difference of the 
amplifiers as a level/tone difference. Since each amplifier was 
driven from the same source, with wide-open level control 
settings, this seemed like a valid first-guess at an answer. 

After poking at the problem with a calculator for an hour, I 
decided that it was time better spent by a computer. As a 
result, I developed a database of different amplifier models, 
their sensitivities and power outputs, and then derived some 
additional information about them from the data.
The results are shown in the tables presented on the following 
pages. In addition to the individual data, a particularly useful 
way to look at each unit would be to normalize it's characteristics 
against one "nornmal" unit. The amplifier picked as the reference 
delivered 100W into 8 ohms with an input signal of 0.775V (0 dBu).

The table columns and their meanings are: 
make/model
one guess 
Input Sens (v) The manufacturer's rated input sensitivity, in 
volts. In some cases, this was derived from the maximum power output 
power and the circuit gain. The circuit gain was either input 
directly in v/v or db, or it was calculated from the feedback resistor 
values shown on the schematic. 
Input Sens (dBu ) The rated input sensitivity, converted to dBu. 
(dB re 0.775V open  circuit)
out. pow. The manufacturer's rated output power, in watts. 
z The manufacturer's rated output impedance for the rated power 
specification.
Out (dBW) The amplifier output power, in dBW (dB re 1 watt).
gain v/v The amplifier's voltage gain, in volts per volt.
gain dB The amplifier's voltage gain, in dB.
Vin for 100W This represents the input signal in dBu required for 100W 
output.
Po for ref input This represents the output power delivered into an 
8 ohm load for the same signal level required to drive the reference 
amplifier to it's reference power output (100W/8 ohms/0 dBu). This 
means that if you hook the UUT (unit-under-test) in parallel with 
the reference amplifier, you'll get 100W out of the reference, and 
whatever the column says from the UUT.
sens diff This represents the sensitivity difference between the 
reference amplifier and the UUT in dB. Negative numbers indicate that 
the UUT is less sensitive (requires more input signal) than the reference.

As it turns out, I've been unable to draw any real conclusions. One 
of the power amplifiers is an old Phase-Linear 400. A glance at the 
table shows three different versions of this amplifier. Until I figure 
out which one is in the rack, all bets are off. The amplifier that the 
band said sounded brighter turned out to have lower input sensitivity 
than the amplifier that they were comparing against. 

Perhaps there is a difference.