So, my 2008 Fit Sport that I bought 2 weeks ago came with an aftermarket stereo, to put it mildly. Already installed were a Sony head unit, a Pioneer DEQ-7600 DSP/EQ, a Orion amp, and a huge speakerbox with two Jensen amps.

I got in contact with the original owner and confirmed the signal path:

The Sony head unit powers the front speakers only. An output (I'm guessing RCA) goes to the Pioneer EQ, then from there, one right and left signal (via RCA) goes to the Orion power amp, which drives the rear door speakers. Another pair of RCA outs goes to the speakerbox, one to each Jensen amp (running bridged), and each amp drives one side of the speakerbox. Neither the head unit's nor the EQ's subwoofer outputs are used. The speakerbox is run at full-range because it has mids and tweeters on top of the box, along with two 12's in the front. There is also a 1/2 Farad capacitor in line with the two Jensen amps. Here's a shot of what it looks like:



I knew when I bought the car that I would be removing that huge box and just going with a smaller sub. I ended up getting a JL Audio CS110-WXv2 10" subwoofer.

So, tonight, I set out to remove the speakerbox that was taking up all of my cargo area and drop in the little JL Audio sub. I disconnected the power wires to the Jensen amp on the left from the distribution block, removed the remote terminal wire, and disconnected the speaker wires going to the speakerbox. I also removed the RCA plug from that amp. Then I removed the other amp, distribution blocks and capacitor from the back of the speaker box, took it out, and saw the floor of my cargo area for the first time.

Then, I mounted the still-connected Jensen amp, the distribution blocks and the capacitor to the back of the new JL Audio Sub. I ran both RCA's to the right and left input of the amp and connected the speaker wire to the JL Audio sub. This amp is still wired in bridged mode. Here's two shots of the new sub, amp, etc.:





These Jensen amps have the following controls:



Before I tested out the newly installed sub, I turned the Level control on the amp all the way down, switched the X-Over to LPF and left the LPF knob at halfway. The Bass Boost was left off.

I put in a CD and turned up the volume to what I'd consider my normal "loud-ish" listening level. Then I switched on the sub and went back to the hatch to turn up the level on the amp. I turned the level up to halfway, and all of a sudden, the amp's protection mode kept kicking in and shutting off the amp. I turned down the level first, and the amp stayed on. I tried turning up the level again, and the thermal protection kicked in again. I kept the level where it was at and turned the LPF knob all the way down (to 40Hz), and the amp would stay on. Something else I noticed was that the capacitor's blue LED's were staying on, and the voltage reading was constantly changing (always above 14 volts, though).

I am really not sure what is going on here. The way it was previously wired, the Level was kept on MAX, the X-Over was on Full, LPF and HPF were both in the middle (Bass Boost was off), and the Thermal Protections never kicked on for either Jensen amp.

I don't think it's the wiring because I didn't change anything about the wiring except removing one amp from the distribution blocks and running both RCA's from the EQ to one amp and connecting the speaker wires to the new sub.

The sub and amp should be an OK match as the amp is rated at 150 watts RMS at 4 ohms bridged, and the sub's continuous power handling is rated at 200 watts at 4 ohms.

So, I seek the knowledge of you car audio gurus on here. What could be causing the amp's Thermal Protection to kick on and shutting off the amp at such a low level setting in this set-up?

My initial guess is that maybe since it's receiving a full-range output, not a "subwoofer only" output, from the EQ, maybe it's making the amp work harder than it should be?

Any ideas?

 

sounds like a loose main power conection check the block & amp. fuse and under the hood.
GL!

 

Well, that didn't work.

I checked the power connections, at least at the distribution blocks, the capacitor, the amp and the fuse that's mounted in the cargo area. It still shuts off. I even tried the other amp. Same thing.

I also tried using only one RCA cable in the input, and although I could turn the level higher before it shut off, it still shuts off, and the capacitor lights were still constantly on. I tried different speaker wires, and that didn't work, either.

The only thing I didn't try was not bridging the amp, but I'm not sure whether that will have any effect.

I am starting to think that maybe something is wrong with the JL Audio sub? Could it still be that the amp is receiving a full-range signal instead of a sub-only signal? Not sure why that would make a difference since I have the LPF on the amp turned on.

Any other ideas?

 

Never mind. I believe I have figured it out.

Although it clearly says that the impedance of the sub is 4 ohms on the back of the speaker, my multi-meter says that it's a 2 ohm load.

I have already fired off an email to JL Audio, and I'll be returning this sub to either get a 4 ohm driver (that actually measures 4 ohms on a multi-meter) or just return the whole thing.

Frustrating.

 

Thermal protection can come from a few issues, the most obvious is heat. This can come from a few areas, like too low of a load on the amp or from a lack of air flow. If the other amps function normally then I would rule out air flow. If the amp is truly thermalling then it's usually because of too low of a load which could've happened when you swapped to the new box. I would make sure that you don't have the sub wired to the amp incorrectly.

One last thing that could happen (I've personally had this problem with an amp in the past) is that the thermal circuit could actually be at fault. My problem was the thermal circuit would kick in at 126 degrees instead of the 174 degrees that the amp was designed to handle. Either way in your case I would look into a new amp since the one you have is not in warranty.

 

Thanks for the reply. You must have been typing that up as I posted that the JL Audio subwoofer was measuring at 2 ohms instead of the 4 ohms it's supposed to be. Too low of a load for the amp, obviously.