Power Base Series Power Amplifiers
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:
Example: (A) Find the peak music power of your loudspeaker (such as 75 watts). (B) Find the loudspeaker impedance (8 ohms). (C) Draw a line between points A and B. The line inter- sects the middle scale at the correct fuse value (1.5 amps).
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
2.0volt input, the Power
SENSITIVITY SWITCH INSIDE ACCESS HOLE
1.4 V |
26 dB |
0.77 V |
THIS AMPLIFIER IS EQUIPPED WITH SELECTABLE INPUT SENSITIVITY. REMOVE COVER PLATE (ABOVE) TO ACCESS SENSITIVITY SWITCH.
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| 5 | 6 | 7 |
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| 5 | 6 | 7 |
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| 4 |
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| 8 |
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| 4 |
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| 8 |
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BALANCED |
| 3 |
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| 9 |
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| 3 |
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| 9 | UNBALANCED |
| 2 |
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| 10 |
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| 2 |
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| 10 | ||
INPUT WIRING |
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| INPUT GROUND LIFT |
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| INPUT WIRING | |||||
1 |
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| 11 |
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| 1 |
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| 11 | ||||
+ | TIP |
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| + TIP | ||||
| 0 |
| 12 |
| INPUT | LIFT | INPUT | 0 |
| 12 |
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– RING |
| GAIN |
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| GAIN |
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| (AFFECTS PHONE INPUTS ONLY.) | (MONO) |
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GND SLEEVE | GND SLEEVE |
Fig. 2.4 Input Sensitivity Switch
1.0
1.2
1.4
1.6
2
2.5
3
4
5
6
7
8
9
10
12
14
16
20
25
30
40
Example: Impedance = 8 ohms. Peak Power = 75 W
Answer: Fuse = 1.5 A
LOUDSPEAKER IMPEDANCE (ohms) | FUSE (amps) |
20
15
10
8
6
5
4
3
2
1.5
1
.8
.6
.5
.4
.3
.2
.15
.1
.08
LOUDSPEAKER RATING
3000 |
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2000 |
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1500 |
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1000 |
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800 |
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600 |
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400 |
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300 | power) |
200 | |
150 | average |
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100 | continuousthe |
40 | |
80 |
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60 |
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30 | 4 times |
20 | (Typically |
15 |
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10 |
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8 | MUSICPOWER (watts) |
6 | |
4 | |
3 | PEAK |
2
1.5
1
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.
Fig. 2.5 Loudspeaker Fuse Nomograph
2.5 Required AC Mains
All Power Base amplifiers are shipped with an appro- priate line cord and plug. When possible, use a power receptacle on a dedicated circuit, and always make sure it will provide the right voltage and sufficient cur- rent. 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.
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