Appendix A:
Input Sensitivity Level Setting
Following the directions below will allow the installer to adjust the input
sensitivity of each amplifier channel pair in just a few minutes using equipment
commonly available in installation bays.
Necessary Equipment
• Digital AC Voltmeter
• CD or file with a sine-wave test tone recorded at 0 dB reference level in the
frequency range to be amplified for that set of channels (50 Hz for subwoofer
channels, 1 kHz for a midrange application). Do not use attenuated test tones
(-10 dB, -20 dB, etc.).
The Nine-Step Procedure
1)
Disconnect the speakers from the amplifier’s speaker output
connectors (you need only disconnect one speaker wire).
2)
Turn off all processing (bass/treble, loudness, EQ, etc.) on the source
unit, processors (if used) and amplifier. Set the source unit’s fader
control to center position and its subwoofer level control to
3/4 of maximum.
3)
Set both
“Input Voltage”
switches to
“Low”
and turn both
“Input
Sens.”
controls all the way down.
4)
Set the source unit volume to 3/4 of full volume. This will allow for
reasonable gain overlap with moderate clipping at full volume.
5)
Using the Target AC Voltage chart (at right), determine the target
voltage for input sensitivity adjustment according to the nominal
impedance of the speaker system connected to the amplifier outputs.
6)
Verify that you have disconnected the speakers before proceeding. Play
a track with an appropriate sine wave (within the frequency range to
be amplified) at 3/4 source unit volume.
7)
Connect the AC voltmeter to the speaker output connectors of the
amplifier. Make sure you test the voltage at the correct connectors
(+ and –).
8)
Increase the “Input Sens.” control until the target voltage is observed
with the voltmeter. Note: If excessive voltage is measured with the
control set at minimum (full counterclockwise), change the “Input
Voltage” switch setting to “High” and re-adjust.
9)
Once you have adjusted the amplifier to its maximum low-distortion
output level, reconnect the speaker(s) and listen to the system. The
“Input Sens.”
controls can now be adjusted downward if the amplifier
requires attenuation to achieve the desired system balance.