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When my bought the car, the PCM had been replaced with an Alpine INE-W927HD head unit,and I later replaced the factory Bose main amp with a JL XD700 5v2 amp. It has 2 sets of mono sub outputs ...one set for the door subs, the other set for the rear sub box...all wired into the factory harness.
A little while ago, I started getting a high pitched whine coming from the sub enclosure and believe that its being caused by the little 100W Bose amp that is in the enclosure that drives the subs in there. I looked for a replacement factory sub amp (Bose 416007 I think) amp, but haven't found one...unless I buy the whole replacement enclosure on ebay for about 300 bucks.
My question is...I'm wondering if I can just open up the sub box and rewire it to just bypass the sub amp entirely. There are 2 subs in it, but only a single set of speaker level (or line level??) wires that go into the sub amp, so would have to take the single + and - speaker wires before they get to the sub amp and connect the single + wire that would normally plug into the sub amp and attach the + wires from each of the drivers. Same with the - wire. Its my understanding that each of the sub drivers is 4 ohms.
According to the JL manual, the outputs are: Subwoofer Channel, Mono, all channels driven: 180W x 1 @ 4 ohms, 240W x 1 @ 3 ohms, 300W x 1 @ 2 ohms
Will such a bypass work, and is it as straightforward as I described?
The sub box in the rear contains a pair of 5 1/4" speakers only. The amplifier is in a different location, not positive where though. I thought it varied between coupes and cabs too. Check in the frunk behind the plastic trim. Also try under the passenger seat.
The sub box in the rear contains a pair of 5 1/4" speakers only. The amplifier is in a different location, not positive where though. I thought it varied between coupes and cabs too. Check in the frunk behind the plastic trim. Also try under the passenger seat.
Hmmmm, Are you sure? Here is a pic of the sub opened up, lifted from another post.
Last edited by jlkline; 12-01-2015 at 05:43 PM.
Reason: Added pic
Well I'll be. I've replaced the speakers in the sub box with a pair of Dayton's. For the life of me I do not remember seeing any control box inside there. But I wasn't really paying attention to anything other than the speakers. I'm betting that's a crossover, not an amplifier. Here's a picture from my frunk, 2006 C2S Coupe showing the Bose amplifier part number 997.645.333.06. The PET manuals show it as a booster with option code I680 for the Bose sound system:
Now answering your question, the speakers are normal speakers with +/- leads. Since you have replaced the Bose amp already with a JL, then I'd connect the pair of sub speakers in the rear box directly to the amp, eliminating anything in between. In this case that silver box you are showing could be bypassed.
Well I'll be. I've replaced the speakers in the sub box with a pair of Dayton's. For the life of me I do not remember seeing any control box inside there. But I wasn't really paying attention to anything other than the speakers. I'm betting that's a crossover, not an amplifier. Here's a picture from my frunk, 2006 C2S Coupe showing the Bose amplifier part number 997.645.333.06. The PET manuals show it as a booster with option code I680 for the Bose sound system:
Now answering your question, the speakers are normal speakers with +/- leads. Since you have replaced the Bose amp already with a JL, then I'd connect the pair of sub speakers in the rear box directly to the amp, eliminating anything in between. In this case that silver box you are showing could be bypassed.
It is definitely an amp... a 100W amp. (see this new pic) Its Bose, and is not an orderable part from Porsche and no Porsche part number. Through my research, I've learned that the same Bose part is used in other European cars, like the Audi A8.
You simply replaced the speakers and never had to modify the wiring in the sub, so you didn't have to deal with a bypass which may have other technical implications (resistance,etc), or require special mods beyond the wiring I proposed in my original note.
I hope there might be some other folks who can chime in that have had some experience closer to the one I'm asking about.
you can read what is on the speakers decal, it probibly has the ohm. Probibly 4 ohm. you can rewire from your amp to these speakers. series would be 8ohm, parallel would be 2ohm.
So series; + from your amp wire to one spk +terminal, wire from that spk - terminal to next spk + terminal, then - terminal to your amp - line
Parallel ; + from your amp wire to one spk + terminal , jump wire to next spk + terminal. then - from your amp wire to one spk - terminal, jump wire to next spk - terminal
A high pitched whine like you describe is almost always ignition noise picked up due to a ground fault. Usually found in aftermarket situations where people have wired stuff in. Simple check, does it make the same noise with the engine off? If not then the fix is to methodically check every connection until you eliminate the noise.
you can read what is on the speakers decal, it probibly has the ohm. Probibly 4 ohm. you can rewire from your amp to these speakers. series would be 8ohm, parallel would be 2ohm.
So series; + from your amp wire to one spk +terminal, wire from that spk - terminal to next spk + terminal, then - terminal to your amp - line
Parallel ; + from your amp wire to one spk + terminal , jump wire to next spk + terminal. then - from your amp wire to one spk - terminal, jump wire to next spk - terminal
I think they are 4ohm speakers. Can you have a look at the attached, but very crude sketch that shows what I think you are proposing?
A high pitched whine like you describe is almost always ignition noise picked up due to a ground fault. Usually found in aftermarket situations where people have wired stuff in. Simple check, does it make the same noise with the engine off? If not then the fix is to methodically check every connection until you eliminate the noise.
Chuck, yes, I thought that as well.
The only things I've done to the car lately is remove the sub box ( unplugged and replugged it in at the sub connector)to get to the tops of the rear shocks and then 2 weeks ago I replaced the top idler pulley (no electrical disturbed but that pulley does bolt into the alternator bracketry) I can't imagine this work would have caused this, do you? which is why the amp is suspect. I did go in and disconnect / reconnect the sub again just to be sure that connection was OK...no change
When I shut off the car, I can hear the whine for a second or two longer after the car shuts off before it goes away. It it kind of dissipates but doesn't change pitch.
I'm posting a video recording of the noise...kinda like a tea kettle.
The volume is turned completely down and the volume of the whine nor the pitch never changes. Then at the end you'll he me kill the ignition which shuts everything off.
The only things I've done to the car lately is remove the sub box ( unplugged and replugged it in at the sub connector)to get to the tops of the rear shocks and then 2 weeks ago I replaced the top idler pulley (no electrical disturbed but that pulley does bolt into the alternator bracketry) I can't imagine this work would have caused this, do you? which is why the amp is suspect. I did go in and disconnect / reconnect the sub again just to be sure that connection was OK...no change
When I shut off the car, I can hear the whine for a second or two longer after the car shuts off before it goes away. It it kind of dissipates but doesn't change pitch.
Back many years ago I used to use that same thought process- something's changed, I haven't done anything that would cause this, it must be [fill in the blank]. So for example when a speaker cut out, gosh it must be the amp. But when I ask my professional electronics tech guy to check it out, first thing he does is pick up the speaker and… wires disconnected. See: how to go from Strides the Earth Audiophile to Unworthy Cretin in no time at all. After about a half a dozen of these I eventually understand you need to follow the professional steps and not jump to any conclusions.
So when there's a whine in a car system, you don't worry about what you've done you simply go about checking connections. Check means you take each one apart, examine, re-attach, ensure everything is nice and tight. Use contact enhancers if you have any. The nature of ignition interference is it gets into the signal path at a very low level, which after amplification becomes audible. So you look upstream from the amp- head unit, source, power supply, etc.
In the past these were almost all ignition related. Today though there are so many generators of high frequency radiation you can hardly even begin to count them all. The tipoff and confirmation that's what it is, is that when the ignition is turned off it continues a while but then dissipates and goes away. This is easily explained by microprocessors, etc that remain powered up until capacitors in the circuit slowly discharge.
At this point you have to ask yourself, what could be wrong with my amp that causes it to whine when the ignition is on, but stop whining after its turned off? Its a puzzle, how the amp would know to make bad noises only when the key is on.
Or, the key being on generates RF that gets into the signal path somewhere and amplified to where you can hear it. That one is easy to understand. Granted, it may still be something else, but this is way more likely than the amp knowing when to whine.
Its funny you mention the alternator bracket. I don't know how Porsche does it, but alternators often serve as their own ground. The alternator is grounded to the engine/chassis, with current flowing back to that ground. Bad ground there, bad ground everywhere. Kind of unlikely, unless the whine showed up right after your work, but its more the kind of thing you would be looking for.
Most likely, whoever installed the system, at some point made a connection that has over time worked its way loose enough to be causing you problems. Its still connected, which is why everything works. But its just loose enough to create the conditions for RF to get in. It could be anywhere from the head unit to the amp input.
About the only thing you can be sure of is its not the amp. If it were the amp then it would whine and whine and never stop no matter how long the ignitions turned off.
Back many years ago I used to use that same thought process- something's changed, I haven't done anything that would cause this, it must be [fill in the blank]. So for example when a speaker cut out, gosh it must be the amp. But when I ask my professional electronics tech guy to check it out, first thing he does is pick up the speaker and… wires disconnected. See: how to go from Strides the Earth Audiophile to Unworthy Cretin in no time at all. After about a half a dozen of these I eventually understand you need to follow the professional steps and not jump to any conclusions.
So when there's a whine in a car system, you don't worry about what you've done you simply go about checking connections. Check means you take each one apart, examine, re-attach, ensure everything is nice and tight. Use contact enhancers if you have any. The nature of ignition interference is it gets into the signal path at a very low level, which after amplification becomes audible. So you look upstream from the amp- head unit, source, power supply, etc.
In the past these were almost all ignition related. Today though there are so many generators of high frequency radiation you can hardly even begin to count them all. The tipoff and confirmation that's what it is, is that when the ignition is turned off it continues a while but then dissipates and goes away. This is easily explained by microprocessors, etc that remain powered up until capacitors in the circuit slowly discharge.
At this point you have to ask yourself, what could be wrong with my amp that causes it to whine when the ignition is on, but stop whining after its turned off? Its a puzzle, how the amp would know to make bad noises only when the key is on.
Or, the key being on generates RF that gets into the signal path somewhere and amplified to where you can hear it. That one is easy to understand. Granted, it may still be something else, but this is way more likely than the amp knowing when to whine.
Its funny you mention the alternator bracket. I don't know how Porsche does it, but alternators often serve as their own ground. The alternator is grounded to the engine/chassis, with current flowing back to that ground. Bad ground there, bad ground everywhere. Kind of unlikely, unless the whine showed up right after your work, but its more the kind of thing you would be looking for.
Most likely, whoever installed the system, at some point made a connection that has over time worked its way loose enough to be causing you problems. Its still connected, which is why everything works. But its just loose enough to create the conditions for RF to get in. It could be anywhere from the head unit to the amp input.
About the only thing you can be sure of is its not the amp. If it were the amp then it would whine and whine and never stop no matter how long the ignitions turned off.
OK, so I went in, disconnected the sub, and ran a pair of jumpers from the speaker signal wires in the connector that goes somehow to the main amp outputs I connected the other end of the jumper wires to an external speaker, (a good quality headphone to be more precise) then ran the engine, and the sub signal coming through the headphone sounded fine. I did not get the high pitch noise at all. Volume shouldn't be an issue because the whine always stayed at the same volume. Therefore, it has to either the power or ground wires that power the sub, or the amp itself that is which could have a problem that makes it susceptible to engine electrical interference?
I kinda doubt he aftermarket main amp install is the culprit because I don't really see why the installers would need to even mess with power or ground that goes to that sub cabinet, and wiring looks factory original from the sub,back to wherever it goes in the harness.
Its also a bit odd that the other subs in the doors are not affected, but I don't believe they are powered, so they run directly from the main aftermarket amp.
I understand what you said about the amp in your post, and I didn't know if there was a way to check the power or ground in the wiring that goes up to the sub for interference, but other than the whine, the sub fidelity is fine. ( kinda like "gee Mrs. Lincoln, other than that, how did you enjoy the play")
I could just open up the sub (lotta damn screws!) and run the amp bypass, but I'm not sure if I would have enough power in the main amp to do a good job of running all of the subs. Or I could replace the sub amp if I can find one.
Having trouble understanding where you're getting the noise and where you're not. Part of my confusion is what you're connecting the headphones to. What you call main amp outputs, those are called speaker terminals. Main amp, power amp, whatever, they drive speakers. Pre-amp (head unit) outputs provide signal to the amps. So the signal path goes Source (usually built into head unit), pre-amp (built into head unit), crossovers (optional), power amps, speakers. Noise can come in at any point, but downstream noise will not be heard upstream. So keep using your headphones. Keep connecting them downstream. When you go from no noise to noise, start checking every connection. You're on the right track just keep narrowing it down.
12-01-2015, 04:01 PM
Bose rear subwoofer amp bypass for 997.1 c2
