Hey AMC,

Ive recently bought a sub and amp. Im a little unsure of how to wire it and how to set the amp.

I will be using a HI-LO converter taking the signal from the rear speaker wires out the back of the HU and giving a L and R out. These will be spliced in.
Also splicing into the +12V ignition wire for a remote signal.

The amp is a 2ch bridgable JBL p180.2 amp. Bridged is 4 ohm stable I think.
http://www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/OwnersManual/bp_om.pdf

The Sub is a JBL GT5-12 4ohm SVC.
http://universalfuze.webstarts.com/uploads/GT512Tech_050108.pdf

Set the X-over to LP and approximately 60 Hz.

Now the Questions:

Should I measure the Voltage across the outputs of the HI-LO to set the input voltage on the amp?
Do I set the input to Mono or Stereo?
Ive bridged the 2 ch for 1 output, is it still ok to run the 4 ohm SVC sub (not sure how impedences change)?
Is the input level adjustment similar to gain?
Does the -ve output wire go to the -ve terminal on the box and then to the -ve terminal on the sub?

Thanks heaps, Im quite a noob at this stuff and researched as much as I could.

http://img404.imageshack.us/img404/9258/img0388w.jpg (http://imageshack.us/photo/my-images/404/img0388w.jpg/)

Also splicing into the +12V ignition wire for a remote signal. If the amp has auto signal detect, that shouldnt be needed, but do you have an after market headunit?

Ive bridged the 2 ch for 1 output, is it still ok to run the 4 ohm SVC sub (not sure how impedences change)? It should work perfectly fine.
Is the input level adjustment similar to gain? Yes, iirc
Does the -ve output wire go to the -ve terminal on the box and then to the -ve terminal on the sub? Yes, +'tive to +tive, and -'tive to -'tive

Thanks heaps, Im quite a noob at this stuff and researched as much as I could. All have to start somewhere.

Bolded my answers, someone should be able to correct me if anything isnt right

Using the stock head unit thats why I got the HI-LO converter.

Heres a pic of the other side. Pretty sure it isnt signal sensing?

http://img600.imageshack.us/img600/3531/img0389vge.jpg (http://imageshack.us/photo/my-images/600/img0389vge.jpg/)

Signal sensing amp? Never even seen one, pretty fricken uncommon! The ignition wire will be fine for remote pickup, it just means the amp will be on even if the headunit isn't.

Signal sensing amps are getting pretty common now, and yes this is one.
From the PDF

If your
radio has only speaker-level outputs, you
should connect them to the speaker-level
input connectors, observing proper
polarity. When using the speaker-level
inputs, it is not necessary to connect a
wire between the “remote” terminal of
the amplifier and the “remote” lead from
the source unit. The speaker-level inputs
will sense voltage on the speaker
outputs and turn the amplifier on
automatically.

Bridged @ 4 Ohms - you have around 360 Watts on tap. A good amp choice for that woofer.

Keep your Amp Negative (Earth strap) Short less than 30 cm's.

Run your power lead, grommeted through the fire wall so it wont rub and wear through, resulting in a short.
Also keep in mind all power through the firewall must be fused, usually within 30 cm's of the battery.

Any more Questions, hit us up ;)

Using that Hi/Low converter you bought will disable the amps auto turn on mode, I'd take that sucker back to where you got it.
The amps that have Hi Level input turn on, have just combined the power from the speakers with the amp turn on trigger wire input resulting in turning the amp on, easy.....

Turn the X-over switch to Low Pass, and you'll probably end up with the Freq dial set between 80 - 100 Hz, 100 being the ideal place to start.....

Go easy on the gains... And if you have not set gains before, get assistance, and choose your helper carefully, most think they know what do, few actually do, and fewer actually do it well.

Im jelly. I want a signal sensing amp now :P

Using that Hi/Low converter you bought will disable the amps auto turn on mode, I'd take that sucker back to where you got it.
The amps that have Hi Level input turn on, have just combined the power from the speakers with the amp turn on trigger wire input resulting in turning the amp on, easy.....

Turn the X-over switch to Low Pass, and you'll probably end up with the Freq dial set between 80 - 100 Hz, 100 being the ideal place to start.....

Go easy on the gains... And if you have not set gains before, get assistance, and choose your helper carefully, most think they know what do, few actually do, and fewer actually do it well.


hey SH00T you appear to be a guru on car audio from all the other threads ive seen.

If i take the signal from my rear speaker wires in the boot to run the amp for the sub, how would I re-hook up the rear speakers with that configuration? (was unsure so I bought the Hi-lo converter, also unsure how I would use the high level inputs with those weird connectors)

Have nobody to help with gains :P I assume given convention id turn the input voltage all the way to the left (4V) side then slowly turn it to the right (250mV) to increse.

Lastly is the input mode mono or stereo?

Cheers to all the guys who helped BTW.

Im jelly. I want a signal sensing amp now :P
Oh no you don't, I've only seen it with high level inputs for car audio, strange, the low level turn-on is in Home Theatre Equipment though.
Perhaps its because we don't get the variation in sub voltage signal output, as Head units now do.


hey SH00T you appear to be a guru on car audio from all the other threads ive seen.
Ha Ha Thanks, but I'm no Guru, I just read the Manual.



Have nobody to help with gains :P I assume given convention id turn the input voltage all the way to the left (4V) side then slowly turn it to the right (250mV) to increse.

This is correct, 4 Volt is the lowest setting, by providing the least assistance to an incoming signal.
As opposed to 250mV which provides the most assistance (Boost if you will). This is the Danger side, when boosting the signal too much, the upper and lower curves of the wavelength will not fluidly power the speaker in and out. As the wavelength grows, it can exceed the power of the amp, the upper and lower curves wont have power to them and they flatline.
http://t2.gstatic.com/images?q=tbn:ANd9GcTG4ldcSWNuqa8bEpqO6u1dtCqwpnxiw ls9eCD9l-FJr9oonHUC
This wil stall the speaker at each peak, causing it to overheat, and sound like poo, often a slapping sound, it means death to the speaker.
This is called clipping. Youtube it, you can see how quickly a speaker can die.




Lastly is the input mode mono or stereo?

Bridging an amp, takes a stereo capable amp and puts it in Single channel mode - Mono is the correct setting.


hey SH00T you appear to be a guru on car audio from all the other threads ive seen.

If i take the signal from my rear speaker wires in the boot to run the amp for the sub, how would I re-hook up the rear speakers with that configuration? (was unsure so I bought the Hi-lo converter, also unsure how I would use the high level inputs with those weird connectors)

The Manual is very vague here, normally I suspect the high level inputs offer no resistance to an Amp and you'd think would added before or after a speaker, wired in line (series).
But High level Inputs can be wired in place of a speaker, so I suspect this not to be true, and it may offer up 4 Ohms resistance. Or it may fluctuate depending on the power source.
I would place an Email (then its in writing) to JBL Australia, if its safe to wire with speakers as well, and the method they recommend.

But for a fool proof method, with the best results, Get a AfterMarket Head unit (with Sub RCA's or more), run some splits up the front, and a woofer at the rear, and get a really impressive sounding system.....

Cheers for explaining what clipping was had heard it before but wasnt sure what was actually going on.
Will set it to mono and give messing with the gain ago when I get it all hooked up next week.

It seems like I can wire in speakers and a bridged sub but it seems to want me to add capacitors and inductors to make sure the neccesary sounds go where they should.
I think the simplest method is just rocking the HILO converter and letting the amp be on when the car is which is fine because i usually listen to music.

Looking for a cheap set up because the car only cost $300 and I already sunk enough money into it with a DIY respray, and speaker replacement.
HU is out for now.

Cheers SH00T.

You won't need a cap, they help out if the power supply is a tiny battery or alternator, when the instant power demand can't be filled, a cap should only be considered if you cant supply power to a 1000 + watt system, you do not need it. You would get better sound from 90 dollar fusion splits than a 150 dollar cap.
Go with what you have, for now. Good Luck.....;)

One thing I would do though, see if you like the idea, put a switch in the line for the wire you will use for the power-on signal wire, its handy if you have fuddy duudy's in the car that will hate the Bass, or if you have a belting headache, or if you are having battery issues, or your battery just doesn't crank like it should and just needs a good charge off the alternator....
Also, if you are motivated enough, you could Earth the chassis to the motor, and from the same place on the motor to the battery Negative.
This will ensure a good earth to the alternator ground and to the Batteries Negative terminal, ensuring a good power return loop, this will let you get get every ounce of power from that little amp that you can:).

Depending on the amount of wire Ive got left I'll probably do the proper grounding.
For the amp ground is the back of the seat a good point? Not sure whats under the floor and dont want to screw into it incase I hit somthing.

If I can find a switch laying around I'll throw it in seems like a good idea.

Depending on the amount of wire Ive got left I'll probably do the proper grounding.
For the amp ground is the back of the seat a good point? Not sure whats under the floor and dont want to screw into it incase I hit somthing.

If I can find a switch laying around I'll throw it in seems like a good idea.

to ground my amp, i used a bolt behind the bottom of the back seat.

just remember to sand it back to bare metal