If the switch was in the wrong (non-premium/amp'ed) position, would I still have the subwoofer-level control existing in the menus?

Can someone without the premium/amp+sub setup please confirm if they do or do not have an option for subwoofer level after the bass/treble/balance/etc. controls?

 

If ANY speakers are working, then the switch is in the right place - flipping the switch changes output of the head unit from using its internal amps to sending the signal to the trunk power amp, and turns off the sub menu.

All speakers in a premium sound car are wired to and driven by the trunk amp. The subwoofer signal is also crossed over and sent to the subwoofer in the trunk amp. SO, with premium sound, if any speakers are working, the sub should (assuming your head unit has the sub setting, which it does). If the sub isn't working it's either the amp or the speaker (or a problem in the head unit that prevents it from sending the sub volume info to the amp via AiNet - not very likely, all other settings are working like fade and balance, correct?). If you measured no AC voltage across each pair of sub wires (there are two pairs), then it's likely the amp.

 

Thanks, except I measure for DC voltage, so I need to go back and try again for AC and continuity...

My multimeter can read negative volts in DC, so technically an AC signal should still show up in DC albeit at a significant lost of volts but DC held 0.0v consistently so I am not hopeful.

What is the best way to isolate the issue to the sub (or not the sub), touch an audio-source output (iPod) to the sub contacts?

 

I'm not questioning your electrical knowledge, but rather I'm questioning mine. Is the voltage converted to AC when it passes through the amp? I've been thinking that wrong all along.

 

All audio signals are the equivalent of an AC signal - it is a sum of many frequencies, that go both positive and negative relative to ground. By default, this is a MUST as the speaker needs to be driven to both sides of center (0 volts) to maximize its useful range and to minimize distortion.

The signal sent to the speaker is a varying voltage centered about zero - an audio signal with frequency varying between 20 and 20,000 Hz (or 20 and 200 or so for the sub). Since they spend an equal time above and below zero volts, there is no DC component, so measuring with meter set to DC will see the average of the audio signal, which is ZERO.

You can't measure AC with the meter set to DC, the sine wave's average is zero and that's what a DC meter will display. Measuring with the meter set to AC will tell you what the peak (or RMS, depending on your meter) varying voltage level is.

Using the AC meter to measure from your wall sockets sees just 60 Hz (or 50 in the UK). Many meters are optimized for accuracy at this frequency and may be somewhat off at others, especially as frequency gets high... but in our case, we don't care about accuracy, just whether it's there or not. The AC meter will be seeing a varying frequency, but is still able to measure and display a value - and that's all you're looking for - a value that is changing with time and with volume of the music content. It will likely peak at 12V, but could be small... depending on your volume control setting.

If you see no signal at either pair of leads to the sub, when you have the stereo running nice and loud (you can hear it loud in the door speakers) then something is going on in subwoofer section of the amp... period.

Ebay has XJ amps relatively cheap at times - and the amp is extremely easy to swap out. What is the value of your time? Running down other possibilities will just waste more of it.

I'm an electrical engineer, specializing in troubleshooting difficult systems. With the symptoms you've described to date, and with verification that there's no AC voltage across both pairs of sub leads, the first thing I'd do is replace the amp. Actually, I'd disassemble and troubleshoot the amp to find what has failed, and repair it... but I don't expect you to do that - $100 for replacement is reasonable.

Caveat - the sub may also be damaged - did you measure the resistance across each pair of the subwoofers connectors (on the sub, not the cable to the sub - disconnect the cable first)? you should see between 4 and 8 Ohms each. Also, the surround of the cone can be damaged - you can inspect with a strong flashlight thru the speaker grill - look for cracks or missing areas in the rubber, curved diaphragm surrounding the cone. Replacement surround kits are available for around $15, are easy to install and work perfectly - I have done this to mine.

 

Thanks quad, still have yet to do the AC/continuity check, but there is absolutely no visible physical damage when looking from within the trunk.

Your remark about AC sign-wave counteracting each other actually indicates that a flat 0v in DC (rather than my multimeter searching for current which it does with an open-circuit) may mean the subwoofer is actually getting a signal...

I apparently forgot my EE education when I tested in DC, most amps have in-series capacitors for filters which would totally block DC current...

 

I was going to discuss DC blocking caps in my hour-long monolog above, but it started getting too deep already, lol... NOW, don't get me discussing Class D amplifiers. I don't know whether the jag uses Class A/B or class D, but for your measurements, it's not going to make much difference.

Bottom line, you are correct - by measuring with the meter set to DC voltage, there could well have been a signal there, but you didn't see it... set to AC you will, if it's there.

 

I'm a huge audiophile. I believe the Jag amp is class a/b since class A would be too expensive and I'm guessing the amp is too ancient to have a high chance of being class D.

The 1995 XJ6 harman/kardon system had this large extremely impressive looking amp plainly visible in the trunk. It looks impressive on the outside, but its filled with trash Toshiba IC class A/B channel amps. I bet the Alpine system is very similar.

What does everyone think about the Jag premium system? Does the Harman/Kardon system sound any different than the Alpine system?

The alpine door woofers are pretty decent, but the sub can hardly handle much loud bass and actually only provides modest additional bass depth over the door speakers. The front tweeters are cone tweeters I believe and create a weak soundstage as a result with harsh treble. The rear soft dome tweeters seem to have decent potential with smoother highs than the fronts but they are ruined by a lone capacitor (!) serving as a crossover and microscopic sized magnets. However, the overall the sound actually comes together pretty well. Rear seat passengers often complain that the music isnt playing in the back b/c of the weak rear tweeters.

I would guess it does about 80hz-15khz?

 

I recently blew my sub in my 2002 XJR and am considering replacing it with a box or tube in the trunk since it does not produce much. I saw it was installed from the top. I will need to remove it so it is not flapping in the wind and am a little confused why the back seat has to come out to slide out the rear shelf. It looks like I could remove the child seat anchors and lift the leather finish piece on the shelf, then the grill to get to the screws. I must be missing something from your post and experience.

 

Okay, verdict seems to be the amp - there is no AC signal leaving the amp on the two sub channels, the other channels indeed have fluctuating AC voltage. (tested by removing harness-plug and sticking probes into the amp's harness female-connector)

Also, the subwoofer has the exact same resistance on both channels (I think it was 2.6ohm,) does that imply that it does indeed work or it still may be dry-rotted nevertheless? (tested by probing the harness once disconnected from the amp) What could I safely hook up to the subwoofer leads to test that it functions? I thought about a boombox speaker-connector, but I think those are designed for 8ohm speakers??

 

Any high level audio source (speaker output) will work - don't worry too much about the design impedance unless you plan on blasting it.

I usually use a single 1.5V battery (anything from AA to D) in a holder (from Radio Shack) with wires from the battery holder to test a speaker (or sub).

Just briefly connect the wires from the holder to each pair of speaker terminals and immediately disconnect - just touch for a split second - you'll hear a nice deep 'thump' if it's working, nothing if it's not, and a scratchy, scraping sound if the cone or voice coil is damaged. Do this for both terminal pairs on the sub.

 

Battery trick is clever, going to try that thanks