MTX Audio 421D Installation, Adjusting the Gain, Typical Speaker Wiring Configurations

POWER AMPLIFIER OWNER’S MANUAL

Installation

Any deviation from the connection specifications recommended may cause serious damage to the amplifier, speakers and/or vehicle electrical system. Please double-check the connection before turning the system on.

1.Disconnect the vehicle’s negative battery connection.

2.Place your Thunder amplifier at the predetermined mounting location. Using a felt pen, mark the exact position of the mounting holes on the mounting surface. Set the amplifier aside. Use a sharp, precise blade to cut small circles in the carpet and padding around the four marks denoting your mounting holes to expose the metal underneath. Use a center punch to make an indentation in the metal to ensure that you drill the exact position for the screws. Drill the four holes as marked.

3.Temporarily mount your Thunder amplifier.

4.Run a power cable from the vehicle’s battery through the firewall and through the interior of the vehicle connecting one end to your Thunder amplifier’s +BATT terminal and connect the other end to the positive post on the battery.

Note: Install a circuit breaker/fuse within 18" of the battery. This effectively lowers the risk of severe damage to your vehicle should a short circuit ever occur in the audio system. Do not install the fuse in the fuse hold- er until all installation steps have been completed.

Adjusting the Gain

1.Turn the gain control on the amplifier all the way down.

2.Turn up the volume control on the source unit to approximately 3⁄4 of maximum.

3.Adjust the gain control on the amplifier until audible distortion occurs.

4.Adjust the gain control down until audible distor- tion disappears.

5.Follow steps 3-4 for other gain control settings if applicable.

6.The amplifier is now calibrated to the output of the source unit.

Typical Speaker

Wiring Configurations

5.	Find a good ground spot on the vehicle’s chassis and remove the paint to reveal bare metal at the contact
	point. Attach the ground wire to that contact point and connect the other end of the ground wire to the
	GND terminal of your Thunder amplifier.
6.	Connect a Remote Turn-on wire from your source unit to your Thunder amplifier’s REM terminal (14 or 16
	gauge wire). If your source unit does not have a dedicated Remote Turn-on lead, you may connect to the
	source unit’s Power Antenna lead.

Troubleshooting Guide

Read this if you wanna be a do-it-yourselfer or give us a call at 800-CALLMTX.

7.	Connect RCA cables from your source unit to your Thunder amplifier’s RCA input jacks. If RCA (low level)
	output is not available, connect the included speaker (high level) connector (Thunder421D, Thunder801D)
	to the speaker wires from the source unit.
8.	Connect your speakers to your Thunder amplifier’s speaker terminals using 12 gauge minimum speaker
	cable.
9.	Double-check all the previous installation steps, in particular, the wiring and component connections.
	Securely mount the amplifier. If everything is in order, reconnect the vehicle’s negative battery connec-
	tion and begin adjusting your amplifier.

Note: Be sure that the Gain Level on the amplifier is turned all the way down (counter clockwise) before pro- ceeding with adjustments.

Common Oversights

•The battery ground should remain DISCONNECTED at all stages of installation.

•Do not begin drilling until you have put your Thunder amplifier aside. Using the amplifier as a drilling guide may cause irreparable damage to the amplifier and void your warranty.

•Do not route any wires underneath or outside the vehicle body.

•Route signal wires (RCAs from source unit, speaker wires, etc.) away from power wires (power, ground, etc.) to avoid ground loops and other sources of noise.

PROBLEM	CAUSE
No LED indication	No +12V at remote connection
	No +12V at Power connection
	Insufficient ground connection
	Blown power fuse
LED on, no output	Volume on head unit off
	Speaker connections not made
	Gain control on amplifier off
	Signal processing units off
	All speakers blown
Output distorted	Head unit volume set too high
	Amplifier gain set too high
Balance reversed	Speakers wired L + R reversed
	RCA inputs reversed
Some balance reversed	Some Speakers wired L + R
	reversed
	Some RCA inputs reversed
Bass is weak	Speakers wired out
	of phase
	Not using MTX woofers
Blowing fuses	Excessive output levels
	Amplifier defective

SOLUTION

Supply +12V to terminal Supply +12V to terminal Verify ground connection Replace fuse

Increase volume on head unit Make speaker connections Turn up gain

Apply power to signal processor Replace speakers

Lower head unit volume

Lower amplifier gain

Wire speakers with correct orientation

Reverse RCA input

Wire speakers with correct orientation

Reverse appropriate RCA inputs

Wire with correct phase

Buy MTX woofers

Lower volume

Return for service

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