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Fact Sheet: About Power Amplifier Sensitivity |
Amplifier Sensitivity
is not Power!
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First, please know that "sensitivity" is not the same as power. It doesn't matter whether you chose the low or high sensitivity option, the amplifier will have the same power output. What will change is how loud you set the volume control (among other things).
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Think
of sensitivity the same way you think of loudspeaker efficiency: a
very efficient speaker doesn't need many watts to play loudly, whereas
a low-efficiency speaker needs more watts to play at the same level.
By the same token, a high-sensitivity power amplifier does not need
much of a signal from the preamp to play at full power, where a low-sensitivity
power amplifier needs more preamp drive to reach the same power. |
Let's assume you want to play a recording of a singer at a realistic level. With a high-sensitivity amplifier, you might only need to set your preamp's volume control to 9 o' clock to make her sound as loud as a real singer would. With a low-sensitivity amplifier, you will need to set the volume control to maybe 12 o' clock to get the same loudness. She'll be just as loud either way.
This can be handy if you have high-efficiency speakers and find yourself generally listening with the volume control barely cracked open. Going to the low-sensitivity amplifier will let you use a more useful range of the control.
The low sensitivity version will have a couple of extra added benefits: 1. Residual background hiss and noise from the preamp will be less audible in the listening position, and 2. the kind of tubes that have less amplification factor (the sensitivity of my amplifiers are determined solely by the amplification factor of the tubes, not by feedback) are more linear, with less distortion. They sound a smidge more natural.
However, the low-sensitivity version is not right for everyone. If you like to listen to music REALLY loudly, or have low-sensitivity speakers, you might find that you can't turn the volume control on your preamp up far enough to have the music play loudly enough for you! Also, some preamp, notably transistor ones, simply can't put out enough volts to drive the low-sensitivity version to full power: they just run out of volts.
Use these guidelines:
- NP100: Use the low-sensitivity version if your speakers are moderate to
high sensitivity AND your preamp's maximum output level is more than 4V
r.m.s. (11V peak-to-peak), AND it boasts more than than 16dB of voltage
gain in the line section. But, if you are not sure or like to listen to
really loud music, go for the high-sensitivity version. (Check with the
preamp manufacturer for maximum output level and gain.)
- NP220: Use the low-sensitivity version if your speakers are moderate to high sensitivity AND your preamp's maximum output level is more than 6V r.m.s. (17V peak-to-peak), AND it boasts more than than 20dB of voltage gain in the line section. But if you are not sure or like to listen to really loud music, go for the high-sensitivity version. (Check with the preamp manufacturer for maximum output level and gain.