Input Sensitivity Adjustment; Additional Load Protection; Required Ac Mains - Crown POWER-TECH 3 Reference Manual

2.3 Input Sensitivity Adjustment

The input sensitivity switch inside the amplifier is set to
0.775 volts at the factory.* It can be changed to 1.4 volts
or a voltage gain of 26 dB as follows:
1. Turn off and unplug the amplifier from the AC source.
2. Remove the access cover on the back panel.
3. Locate the labeled access hole for the sensitivity switch.
4. Set the switch to the desired position.
5. Replace the access cover plate.
When set to 26-dB gain, the Power-Tech 1 requires a
2.1-volt input, the Power-Tech 2 requires a 2.6-volt input
and the Power-Tech 3 requires a 3.3-volt input to deliver
full output into an 8-ohm load.
Fig. 2.4 Input Sensitivity Switch

2.4 Additional Load Protection

To protect against excessive power, a fuse can be
added in series with each loudspeaker cable. A single
fuse can protect the entire system, or one can be used
for each driver. High-frequency drivers (tweeters) are
usually more sensitive to large voltage peaks, while low-
frequency drivers (woofers) are typically most sensitive
to the heat from average (RMS) output power. To protect
your tweeters, we recommend that you use a high-speed
instrument fuse like the Littlefuse 361000 series. To
protect your woofers, we recommend using a slow-blow
fuse that more closely represents the thermal response
of your woofer. Use Figure 2.5 to find the correct value for
either type of fuse.
Example: (A) Choose the peak music power for the
loudspeaker (such as 75 watts). (B) Find the
loudspeaker impedance (8 ohms). (C) Draw a line
between points A and B. The line intersects the middle
scale at the correct fuse value (1.5 amps).

2.5 Required AC Mains

All Power-Tech amplifiers are shipped with an appropri-
ate line cord and plug. The standard cord and plug for
* Factory setting for international models is 1.4 V.
Page 8
Fig. 2.5 Loudspeaker Fuse Nomograph
each model are listed by country (or region) in
Figure 2.6. When possible, use a power receptacle on
a dedicated circuit, and always make sure it will
provide the right voltage with sufficient current. We do
not recommend operating your amplifier with voltages
greater than 10% above or below the unit's rated
voltage. For example, if your amplifier is rated for
120 VAC, the line voltage should not exceed 132 VAC.
Fig. 2.6 AC Mains Cords and Plugs
Power-Tech Series Power Amplifiers
Reference Manual