Crossover Frequency Adjustments, Number

GTH400-20107 06/03/98 15:49 Side 12

4.2 Internal Adjustments

Speaker-Level Input

Impedance Adjustments

The speaker level inputs of the GTH400 come factory set with 100k ohm input impedance. This will provide the lowest distortion operation from the speaker outputs of most modern head units by reducing the power the amplifier in the head unit must deliver to practically nothing. On some older, or lower-priced head units, this load will not facilitate proper fader operation. To allow for this, we have provided the ability to change the input impedance of the speaker-level inputs to 15 ohms. This is accomplished by moving the jumpers

JUMPER SELECTOR

SELECT 100K OR 15 OHMS

			150HMS	100K
			150HMS
	SPEAKER	150HMS	100K
	SPEAKER			LINE
	INPUT			INPUT
	IMPEDANCESELECTOR
150HMS	100K
150HMS				PREAMP
100K				OUT
150HMS

shown on the diagram above. This in- put is also capable of directly accepting signals, when in the 100k ohm setting, from many Balanced Line Drivers such as those sometimes used in competi- tion vehicles. For best results, a Balanced Line Driver capable of at least 4V nominal output should be used.

If the head unit has 4 channels of built- in amplification and/or an electronic fader control, you should leave the jumpers in the factory set position.

If the head unit has 2 channels of amplification, with a speaker-level fader, the jumpers should be set to the 15-ohm position. This will always be a

rotary-type control, not one controlled by electronic pushbuttons.

If you are not certain of the type of fader control your unit has, measure the resistance across one set of speaker outputs with an ohmmeter (with the head-unit off). Adjust the fader control through its entire adjustment range. If there is a change in the resistance as the control is adjusted, set the jumpers to the 15-ohm position. (See step 1, page 16 to remove bottom cover.)