Broken amp or Sub?

[nicster 10+ year member]

Hello,

I recently aquired a Legacy 300 watt 2 channel bridgable amp, and a jbl 10" loud and clear sub. I hooked it all up (I'v only done this about 4 times) and i go to turn on the sub and all i get is a little bit of vibration from the sub. A pretty low tone. Does anyone have a clue what might be the prob? This is for my brothers g/f So it was suposed to be under a 100(which it was off ebay, all new) I am using the high-inputs because of her factory stereo. Any help would be great.

Amp- Two Channel Bridgeable Output

2 x 150 Watts Total Output

1 x 300 Watts Output Bridged Mono

MOSFET Power Supply

Variable Gain Control

Built-In Subwoofer Crossover

Gold Plated RCA Inputs

High Level MOLEX Input

Speaker Impedance: 4-8 Ohms

Easy Access Speaker Connections

Soft Turn-On Circuit

Remote Turn On/Off

Thermal Overheat Protection

Speaker Short Circuit Protection

Input Overload Protection

Heavy Duty Aluminum Alloy Heatsink

Power On LED Indicator

Protection LED Indicator

Frequency Response: 15-30kHz

Signal to Noise Ratio: 95dB

Dimensions: 8"W x 2"H x 10"L

Sub - JBL LC-S1050W 4 OHMS, 400 WATTS PEAK, 100 WATTS RMS, SENSITIVITY 92dB, FREQ RESPONSE 38 - 800Hz

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[kottonmouth 10+ year member]

it could be your ground or some wires behind the head unit could be lose.

 

[chris229 10+ year member]

make some muting plug by hacking off the ENDs of some RCAs. Short out the plug by connecting the center prong and the outer ring. Have enough muting plugs to plug in ALL channels to mute the AMP. The plugs create 0 volts with 0 impedance across the inputs of the AMP. If it makes noise the AMP is the problem get it?