Crown 2, 3, 1 manual Input Sensitivity Adjustment, Additional Load Protection, Required AC Mains

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 Base-1®requires a

2.0volt 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.

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.

CH-2 CH-1

			5	6	7					5	6	7
		4				8				4			8
BALANCED		3				9				3			9	UNBALANCED
		2				10				2			10
INPUT WIRING								INPUT GROUND LIFT						INPUT WIRING
		1				11				1			11
+	TIP													+ TIP
			0		12		INPUT	LIFT	INPUT	0		12
– RING			GAIN							GAIN
								(AFFECTS PHONE INPUTS ONLY.)	(MONO)

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
2000
1500
1000
800
600
400
300	power)
200
150	average
100	continuousthe
40
80
60
30	4 times
20	(Typically
15
10
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. 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.

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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