Power Base Series; 2.3 Input Sensitivity Adjustment; 2.4 Additional Load Protection- Page 10

Power Base Series

  Power Amplifiers

Page 10

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 Base-1

®

 requires a

2.0 volt input, the 

Power Base-2

®

 requires a 2.5 volt in-

put and the 

Power Base-3

™

 requires a 3.2 volt input to

deliver full output into an 8 ohm load.

0.77 V

26 dB

SENSITIVITY SWITCH INSIDE ACCESS HOLE

1.4 V

THIS AMPLIFIER IS EQUIPPED WITH SELECTABLE INPUT SENSITIVITY. REMOVE COVER PLATE (ABOVE) TO ACCESS SENSITIVITY SWITCH.

CH-2

INPUT GROUND LIFT

(AFFECTS PHONE INPUTS ONLY.)

(MONO)

INPUT

GAIN

CH-1

INPUT

GAIN

LIFT

BALANCED

INPUT WIRING

+

–

TIP

RING

SLEEVE

GND

UNBALANCED

INPUT WIRING

+

TIP

SLEEVE

GND

0

1

2

3

4

5

6

7

8

9

10

11

12

0

1

2

3

4

5

6

7

8

9

10

11

12

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 sen-
sitive 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 cor-
rect value for either type of fuse.

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).

1.0

1.2

1.4

1.6

2.5

3

4

5

6

7

8

9

10

12

14

16

20

25

30

20

15

10

8

6

5

4

3

2

1.5

1

.8

.6

.5

.4

.3

.2

.15

.1

.08

3000

2000

1500

1000

800

600

400

300

200

150

100

80

60

40

30

20

15

10

8

6

4

3

2

1.5

1

LOUDSPEAKER IMPEDANCE

(ohms)

FUSE

(amps)

LOUDSPEAKER RATING

PEAK MUSIC POWER

(watts)

(Typically 4 times the continuous average power)

Answer:  Fuse = 1.5 A

2

40

Example: 

Impedance = 8 ohms.

Peak Power = 75 W

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.