Help with stereo system - JL sub not working

[All Seas]

Hey guys,

We picked up our new to us 2012 ar240 recently and noticed we are having some audio issues. The previous owner installed a jl sub and a 600/6 amp.

it looks like the 4 factory speakers are fed from channels 1-4 and the sub is on a bridged 5/6.

The sub and the front left speakers are not working. Ive traced the wires and looked for broken connections but did not find any. This is on the factory jbl head unit as well with no pre outs for a sub.

My instinct was to swap the head unit for one with the proper Pre outs and rewire it all but not sure if there is a way to test the amp/speaker before doing so.

I am not a big audio guy so any help is appreciated. thanks

 

[Scottie]

I'm assuming the amp powers on? If so, grab an older iPhone, any Android phone, or anything else with a headphone jack. You can connect it to the RCA inputs of the amplifier with a 1/8" stereo to RCA cable. Play some music on your device and you should hear it through the speakers. If you do, then whatever problem there is lies at the head unit. If you still hear no sound, then you have an issue with the amp or speaker wiring.

 

[All Seas]

I hear music through the other speakers so assume the head unit is fine.

I traced the speaker cables back to the amp and all looks good and tight connections.

I plan to use a small 9v battery to test the sub, is there a way only 1 channel of an amp can go bad?

 

[Julian]

is there a way only 1 channel of an amp can go bad?

Some amps have two sets of input RCAs and a switch to turn the amp from 2 to 4 channel input. If yours is only wired with one set of inputs it is possible the switch is set to 4?

Not the greatest image...but is the "Input Mode" switch set to 2 channel or 4 channel? Try switching that.

 

[Scottie]

I hear music through the other speakers so assume the head unit is fine.

I traced the speaker cables back to the amp and all looks good and tight connections.

I plan to use a small 9v battery to test the sub, is there a way only 1 channel of an amp can go bad?

Yes, all channels are independent and one can blow without affecting the others. Not very common, but chances increase as the amp ages. Same with the head unit. You can lose front speaker output and not rear, or vice versa. Depending on how it's wired to the amp, that could also be something you're dealing with. I suggested the phone test just to rule that out, or point to the problem.

 

[All Seas]

The head unit is the stock jbl unit and has 2 pair of preouts split to the two amps.

I would imagine the headunit is fine as all the other speakers are playing through the same 2 sets of pre outs. I am not an audio guru but all other systems I have had used a pair of dedicated subwoofer preouts. How would a system work without them?

 

[Josserman]

I would try to isolate the issue.

Start with inputs first - do the iPhone test above but plug into each channel.

Take one speaker you know is working, and move the speaker wire from the working channel speaker output to the others.

If it works then it’s either the other wiring or speaker.

If that’s the case, take the speaker that’s not getting sound out, and run a small speaker cable directly to the amp.

Just use process of elimination to figure out where the problem lies, amp, speaker, wires, or headunit.

 

[Scottie]

The head unit is the stock jbl unit and has 2 pair of preouts split to the two amps.

I would imagine the headunit is fine as all the other speakers are playing through the same 2 sets of pre outs. I am not an audio guru but all other systems I have had used a pair of dedicated subwoofer preouts. How would a system work without them?

A dedicated subwoofer pre-out is just a normal pre-out with high frequencies cut out, so its just the bass signal. It's helpful when you want to run normal speakers on one amp, and subs on another etc, as you can just connect the sub out to the sub amp and be done. However, most amplifiers have built-in high and low pass filters that can be adjusted, so having a subwoofer pre-out isn't absolutely necessary, as you could just filter the highs on a standard pre-out with the amp controls.

 

[All Seas]

Great advice here

I will start diagnosing and report back.

Thank you