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Defective amp? Something's wrong with my system! HELP!

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Old 08-24-2006, 08:24 PM
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Exclamation Defective amp? Something's wrong with my system! HELP!

I just made myself a custom fiberglass enclosure, and did a complete sub install in my car. I picture documented the whole process and plan on writing a very detailed DIY for everyone. For now though, there's a slight problem. heres what I have installed:
  • Factory bose radio
  • "4080" like custom fiberglass enclosure (measured to 1.1 cubic feet)
  • JL 12w3v2 subwoofer (wired in parallel for 2 ohms) (recommended 300 watts rms)
  • Rockford Fosgate P325.1 amplifier (rated 325watts rms @ 2 ohms, CEA spec-ed at 398 watts rms @ 2 ohms
  • PAC SNI-35 line output converter
  • 1.2 Farad capacitor that I forget the brand of... i'll check later

Here's a schematic of my hookup:



As you can see, I tapped the signal post-amp and used an LOC to drop the signal so it could enter the amp's low level inputs.

My problem is as follows: quite simply, it is not loud. Now, i dont mean this in a punk teenager "i want the whole neighborhood to be woken up by my sub" sort of way. First off, my brother used the exact same sub in his audi S4 with the older, 300 watt version of the rockford fosgate amp. in his car, even with all the gains pretty low, it bumped hard.

in my car, i have the head unit's bass set to +6, the line output converter's adjustment ***** turned all the way up, the amplifiers gain **** turned to full, and the remote bass **** for the amplifier also turn to full gain. even with my setup like this and playing a song with a very loud bassline, it is not very loud. i can put my head right up to the sub without much discomfort to my ears.

also, the thing that is even more disturbing than the volume, is that the gains are turned up to full. i know that amps distort the music the most with the gain at full, and distortion is the last thing i want.

so, can anyone help me??? ive put so much time and effort into my system, i really hope i can solve this.

some possible explanations (and my rebuttals) ive heard from the audio "experts" at best buy, circuit city, tweeter and the like:
  • Rockford fosgate was recently bought by best buy and their amps are no longer as powerful as they state --- but the amp is CEA tested to 400 watts rms at 2 ohms; isn't CEA the standard? and even so, with the gains at full, it should still be reasonably loud
  • You might have a bad ground and your amp isnt receiving enough power --- but i chose the same ground as everyone else (spare tire mount, sanded and all), and i tested it with an ohm-meter to have very little resistance
  • You tapped into the wrong signal, or maybe try pre-amp --- i tapped into the signal as per the specifications on the sticky thread (Rear left +V -P, Rear right +W/L -B/L ). maybe i tapped into the tweeter ones though? that could explain it.... i tapped in right where the wires go to the little white connector on the bottom of the 6x9's. as for pre-amp, i originally wanted to try that but was scared away by the "differential" signals and i thought post-amp would be simpler... but maybe i should test it for good measure
  • Your enclosure might be too small --- but i measured it, and 1.1 cubic feet is a good size for my sub, especially because its fiberglass, which supposedly acts as if it were "bigger"

i can post pics of all my signal taps and wire connections if that will help...

once again, please help. any suggestions are much appreciated!
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Old 08-24-2006, 08:42 PM
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you may have a messed up LOC or amp. get both tested and see if one of those may be the problem. and best buy did not buy RF to my knowledge, and i sell the stuff at best buy and haven't heard that.

i hope you fix it. sounds like you put way too much time into it to not have it work. good luck
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Old 08-24-2006, 09:20 PM
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I personally used the front pre-amp for my system w/ no problems. Many others have used post-amp. You tapped correctly for post-amp if you did indeed wire as stated above.

A couple of quick checks:

1. Make sure you did not cross one of your wires and have it wired out of phase.

2. Did your bose speaker volume decrease also? If so, disconnect the LOC etc. and see if volume returns.

3. Try disconnecting the speakers and leaving the LOC etc. hooked up to see if this makes a difference. Depending on the LOC impedence, you could be straining the amp.

4. Try running a signal from and Ipod or something directly to the amp and see how it responds.

5. Make sure your LOC is powered up properly.

These tests should isolate the problem.
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Old 08-25-2006, 02:18 AM
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yeah try to single out everything to see if you can find it.

It also might be something stupid like a **** turned the wrong way.. I know it's dumb but you never know.. and I think it'd be worth it just to spin each **** both ways just to make sure.. (My gut is telling me that it's the adjustments on the LOC)

If you STILL can't find what it is.. might i suggest that your box isn't sealed very well... It's usually pretty easy to detect.. put it on a song with alot of steady bass notes (not kicks) and just stick your ear down close to it if there is a bad seal you will hear what I call a fluttering and sometimes you can even feel the air coming out..

I feel like a idiot telling this to you because judging from what you have done this is stuff that you know.. but sometimes it's the easy stuff that you overlook.

Last edited by WikkedOne; 08-25-2006 at 02:26 AM.
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Old 08-25-2006, 10:21 AM
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Originally Posted by jstkilntim
A couple of quick checks:

1. Make sure you did not cross one of your wires and have it wired out of phase.

2. Did your bose speaker volume decrease also? If so, disconnect the LOC etc. and see if volume returns.

3. Try disconnecting the speakers and leaving the LOC etc. hooked up to see if this makes a difference. Depending on the LOC impedence, you could be straining the amp.

4. Try running a signal from and Ipod or something directly to the amp and see how it responds.

5. Make sure your LOC is powered up properly.

These tests should isolate the problem.
1. I stated my connections above (Rear left +V -P, Rear right +W/L -B/L ), and no one has said anything bad about that, so i will assume those are correct. i did get them from the sticky after all. but i will definitely check to see if i crossed any wires in the process.

2-3. I will check all these today too. thanks for the tips.

4. great idea! i have a stereo minijack-to-rca cable that seems like itll work perfectly for this.

5. my LOC doesnt have any power connections... this made me initially very wary of it, because i dont know how it could work without any active power connectors.... maybe just a transformer inside? also, i read something about measuring the input impedance of my LOC with a multimeter and when i did it i got a really low reading of around 7-15 ohms. it should be high resistance, no?

also - i think i might try tapping preamp, just to test it out. can you provide a guide to what the wire colors are going into the Bose amp? maybe i'll just use the search button.... yeah, that sounds good


Tiger: well those guys at circuit city just musta been trying to spread dirt about their competitors.... lol

Wikked: good idea. im not sure a leak should cause this much of a decrease in volume, but i'll defnately check it out.

Last edited by 1145climber; 08-25-2006 at 02:59 PM.
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Old 08-25-2006, 07:05 PM
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Originally Posted by jstkilntim
I personally used the front pre-amp for my system w/ no problems. Many others have used post-amp. You tapped correctly for post-amp if you did indeed wire as stated above.

A couple of quick checks:

1. Make sure you did not cross one of your wires and have it wired out of phase.

2. Did your bose speaker volume decrease also? If so, disconnect the LOC etc. and see if volume returns.

3. Try disconnecting the speakers and leaving the LOC etc. hooked up to see if this makes a difference. Depending on the LOC impedence, you could be straining the amp.

4. Try running a signal from and Ipod or something directly to the amp and see how it responds.

5. Make sure your LOC is powered up properly.

These tests should isolate the problem.
Alright! i did some testing.... hopefully my results can help us solve this:

1. nah, the wiring hookup is exactly as i specified in my first post. none of my signals are out of phase. i did notice though, if there was bass playing and i either turned down the gain of just one channel on the LOC or if i completely disconnected one channel from the amp, the sub plays really loud, but not the clearest or with good quality. im guessing this is just normal amplifier operation due to mis-matched input signal strengths?

2. unhooking the LOC does nothing to the rear speaker volume

3. when i disconnected both speakers at once, the sub might have gotten a little bit loud, but not much. it could have just been that the lack of the music coming from the trunk made the bass sound louder. i dont think this is the problem.

4. i ran a signal directly from my ipod video's headphone out to the RCA input of the subs with my cable. at half volume with the amps gain at 3/4's like it has been for all my testing, my ipod makes the system BUMP... much louder than being driven by my LOC. also, it is muchhhhh cleaner bass. doesnt sound as distorted and it matches the music much better. another important thing is, with the actual setup, the bass was mostly either all or none. like, on huge bass hits, my system would put out some heavy bass.... but on the less heavy stuff, you could barely hear the bass. with the signal coming from my ipod, the bass is much more consistent with what it should be... the loud bass hits are very loud, the medium basslines are medium in volume as they should be, the the quiet background bass is now audible, but quiet as they should be. now, i dont know how the half-volume signal from an ipod compares in voltage and magnitude from the one that is supposed to be coming from my LOC, but if i remember correctly the maximum output of the ipod is a few hundred millivolts? what is the maximum rated input voltage for the "low-level inputs" of my amp? seems to me the LOC, especially at full gain, should be putting out more voltage than my iPod. i could always buy a new LOC for 20 bucks from circuit city and return it if it doesnt fix my problem. too bad i dont have an oscilloscope to look at the LOC output voltages

5. answered above

wikked - i couldnt detect any air leaks, but i'll keep an eye out.
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Old 08-25-2006, 07:20 PM
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Originally Posted by 1145climber
Alright! i did some testing.... hopefully my results can help us solve this:

1. nah, the wiring hookup is exactly as i specified in my first post. none of my signals are out of phase. i did notice though, if there was bass playing and i either turned down the gain of just one channel on the LOC or if i completely disconnected one channel from the amp, the sub plays really loud, but not the clearest or with good quality. im guessing this is just normal amplifier operation due to mis-matched input signal strengths?

2. unhooking the LOC does nothing to the rear speaker volume

3. when i disconnected both speakers at once, the sub might have gotten a little bit loud, but not much. it could have just been that the lack of the music coming from the trunk made the bass sound louder. i dont think this is the problem.

4. i ran a signal directly from my ipod video's headphone out to the RCA input of the subs with my cable. at half volume with the amps gain at 3/4's like it has been for all my testing, my ipod makes the system BUMP... much louder than being driven by my LOC. also, it is muchhhhh cleaner bass. doesnt sound as distorted and it matches the music much better. another important thing is, with the actual setup, the bass was mostly either all or none. like, on huge bass hits, my system would put out some heavy bass.... but on the less heavy stuff, you could barely hear the bass. with the signal coming from my ipod, the bass is much more consistent with what it should be... the loud bass hits are very loud, the medium basslines are medium in volume as they should be, the the quiet background bass is now audible, but quiet as they should be. now, i dont know how the half-volume signal from an ipod compares in voltage and magnitude from the one that is supposed to be coming from my LOC, but if i remember correctly the maximum output of the ipod is a few hundred millivolts? what is the maximum rated input voltage for the "low-level inputs" of my amp? seems to me the LOC, especially at full gain, should be putting out more voltage than my iPod. i could always buy a new LOC for 20 bucks from circuit city and return it if it doesnt fix my problem. too bad i dont have an oscilloscope to look at the LOC output voltages

5. answered above

wikked - i couldnt detect any air leaks, but i'll keep an eye out.

You CAN look at the output of the LOC.. download a program that generates tones "nch tone generator" is one of my favorites. then you can make tones and sweeps and then burn them onto a cd.. play a 40 Hz tone at near max and hook a voltmeter to it.. should get somewhere between 1 and 8 volts..

of course this is easier for me because I can "mute" all the other channels except for the sub..
I'm not saying you should do this.. just that you CAN

but from what you have said I think its the line leveler... i would try another one just to see what happens... also try some new RCAs
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Old 08-25-2006, 07:46 PM
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wikked youre the freaking man. i happened to have nch tone generator from when i was trying to get rid of all the resonant rattling of things in my room with my home audio sub.... it cleaned up the sound soooo much, i really recommend it. anyway, i burned a cd of different tones and played with my multimeter.... not only was the signal coming from the LOC too quiet, but it was not nearrllyyy linear over the range from 30 to 1000 hertz, while my rear speakers were putting out the same volume the whole time (for the frequency range they could hit anyway).... so obviously my LOC was not only distorting my music, but it was also putting out wayyy too little voltage

anyway, i ran to circuit city and bought a cheap 20 dollar LOC by tsunami.... i just installed it and let me tell you, my system works PERFECTLY now... the bass is SOO much cleaner and accurate. i cant believe how much better it compliments my music than before. it is a comfortable volume with all my gains at half and my HU at +4.... when i turn up my remote bass ****, i can have it bump LOUD if im in the ghetto thug mood.

thanks so much for all your help wikked and jstkilntim. - jstkilntim's idea of testing the amp directly from my ipod was BRILLIANT and also invaluable in isolating my problem to the LOC.

as a final note, STAY AWAY FROM THE PAC SNI-35!!!!! it caused me sooo much trouble.
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Old 08-25-2006, 08:36 PM
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glad I could help.. you can also test the output of you amp... using ohms law - here is a link to a calc at the12volt.com that will help http://www.electronics2000.co.uk/calc/calcohms.htm

rock on
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Old 08-25-2006, 11:21 PM
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Glad things went well. However, don't count PAC out yet. Thier products are usually pretty decent. Remember that everyone puts a few lemmons out there, it just seems like you always get them!
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Old 08-25-2006, 11:22 PM
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Originally Posted by jstkilntim
Glad things went well. However, don't count PAC out yet. Thier products are usually pretty decent. Remember that everyone puts a few lemmons out there, it just seems like you always get them!
yeah alright, good call... so everyone, dont be scared off by pac, just be wary
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Old 08-25-2006, 11:30 PM
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Originally Posted by WikkedOne
glad I could help.. you can also test the output of you amp... using ohms law - here is a link to a calc at the12volt.com that will help http://www.electronics2000.co.uk/calc/calcohms.htm

rock on

i guess i could do that, but i wouldnt be sure how... measure the max voltage at the sub and then divide by the resistance to get amperage, then multiply that by the voltage to get wattage? i guess in theory that would work, but you do have to take into account for the varyng resistance at different frequencies, and more importantly, the inductive reactance (yes, now im using big words... im young, but i do know a little about analog circuitry). anyway, i think it would be kind of difficult to get any sort of max wattage reading, but maybe just the estimate of using the wired resistance (2 ohms in my case) gives you a close enough answer.

are there any tools out there to measure power (wattage)?
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Old 08-25-2006, 11:38 PM
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actually the formula for power is Power (watts) = E(volts)^2 / Resistance (ohms)

P = E^2 / R

here is the link that I meant to add but instead i put the wrong one http://www.the12volt.com/ohm/page2.asp

and yeah with the different frequencies... it would be different. but it will give you a good baseline

Last edited by WikkedOne; 08-25-2006 at 11:41 PM.
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Old 08-26-2006, 11:11 AM
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yeah my formula was just a longer, derived formula of that one... but im not sure it would even give a good bassline, because the subwoofer coils have so incredibly much inductance that it would cause different amounts of resistance at different phases in the range of the speaker. i could definitely be wrong though, as maybe the resistance only varies a little.... maybe i should just stop making assumptions and go test it out.... yeah, that sounds good
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