Adamg187

I just finished wiring a subwoofer and amp by grabbing the right rear pre-amp signal from the head unit. The subwoofer is not very loud unless i fade and balance everything to my right rear speaker and turn it up.

I read a post by 99HT saying that the rear speaker is highpass cutoff at 1kHz (although this may not cutoff at the preamp level?).

I would like to grab an amplified signal that is which is not cutoff.. maybe the signal to the subs in the doors.. I read the 99HT artical and I'm not sure I understand what wires to grap to get an amplified high level signal.

Help.

6SPEEDY

You need to tap into the back or front right AND left preamp outputs from the head unit. No wonder you are geting a weak signal, you are only tapping 1/2 the bass! I did the same install (JL sub, Amplifier) and it works great. Email me if I can help you.
Dave

99HT

The pre-amp outputs are not filtered. Connect to the rear L+R pre-amp outputs and use the bare stranded wire for the return shield.

Be sure to get a good solid ground and power connection to the sub amp. You do not want the sub amp to pull DC current through the signal shield connection. You want the majority of sub amp DC current to flow through it's power ground wire.

Adamg187

For a good ground I had to run the Ground wire into the engine compartment and ground to the base of the alternator.. Is there a closer place in the rear of the vehicle that I could ground.. (it looked like all fiberglass back there).

Also, I'm not sure i know what your are saying about not wanting DC current flowing through the signal shield connection. What exactly is this and how can i tell if i'm doing this?
Thanks

lotzahp

Drill a hole thru the body pan (near the storage compartments) and the frame rails are right there. The rails actually separate those compartments. Route the wire thru the hole and seal it up with silicone.

Adamg187

As i mentioned above when I fade to the back the base is good.. I also notice that when I fade to the front the base was almost identical (from the subs in the front), but when I had it balanced it sounded bad.. low bass.. some baffle.. thats when it hit me to try and reverse the polarity.. I reversed the polarity and its alot better now.

The thing is though.. if the back subwoofer is canceled out by the front thats telling you how loud it is... not that loud.

I think I'm gonna take the door apart now and try and get the amplified signal that goes to the subs in the door and send that signal to my amp and sub.. that way i will have the gain that i want.. Please let me know if this sounds like a bad idea before i do it..

It was suggested that since I only am getting the preamp signal for the rear right signal that by getting both left and right preamp signals I will have much 2x the bass.. So before I take apart the doors i think I'll try that.. does anybody disagree with that though.. sounds to me like i'll have the same gain but will be stereo signal to my amp..

Closer_2001

99HT know what he is talking about. Search for his archived threads on the subject. The man is some type of electronics engineer.

99HT

Quote:

{I think I'm gonna take the door apart now and try and get the amplified {signal that goes to the subs in the door and send that signal to my amp {and sub.. that way i will have the gain that i want.. Please let me know if {this sounds like a bad idea before i do it..

VERY BAD IDEA

The pre-amp outputs are all you need to connect to. Do not connect to the sub amps in any way. You need to pick off the HU pre-amp L+R signals to feed the sub amp. The sub amp should have two inputs to connect to. It is slightly possible that the bass from the front subs is destructively summing with the new sub causing wave front cancellation, but I doubt it. Try adjusting the level control on the new sub amp to test the theory or reverse the speaker polarity.

I am now going to try and explain one common type of ground loop to you. I am going to try to explain this as simple as I can without having to type
too much.

In any audio system you want to keep power and audio wires isolated from
each other. All power and audio returns are indirectly connected to the same
"ground". This "ground" is ultimately the alternator case in a car when it is running. The goal is to force the majority of power currents to stay within
the power wires and the majority of audio currents to stay in the audio
wires. You can never totally eliminate amp power supply currents from flowing in the audio return shields, but you can minimize them by proper wiring techniques.

In a modified C5 Bose system, only connect the pre-amp output signal return shields to the HU bare wires and plug the end of the cable RCA connectors directly into the new sub amp. Try to run the sub power cables as close to the battery as possible. The battery will be a lower noise point to pick off power then the back of the alternator. Never run audio and power cables in parallel along the same path. You don't want them to couple to each other.

In the C5 Bose system, audio signals are sent between the various Bose modules using a differential wiring scheme. A differential wiring scheme is
insensitive to ground loops if left undisturbed. When you tap off the pre-amp outputs directly at the HU, your new wires are connected to the low impedance outputs of the pre-amp buffers. You will not disrupt the Bose system doing this tapping with the standard low level inputs of a sub amp. Tapping audio at other points in the Bose system could introduce noise into the audio.

99HT

P. S.

Are you loading the sub speaker properly? A speaker that is not in a proper enclosure will sound like crap.

Adamg187

Ok.. I will definitely not get a signal from the bose sub amps (don't want any noise)..
I checked and rechecked my power and ground for the amp because I noticed that the power led was dimming every time there was a loud bass signal. I finally figured out that it was the trigger wire and that since i was using the same trigger for my radar detector that the amp was not getting enough current from the trigger.
I now have the right and left rear preamp signal, but I'm using the light blue common ground wire.. i think you mentioned using the bare wire? I'm not getting any noise so i may leave it.
The box I built myself its exactly 1 cu. ft internal volume. with stealth fit which fits flush in the well in the back.. plus enough room for the changer.. the box is solid and the speaker has no distortion.. just did not have enough gain.. but you mentioned plugging RCA's into the amp from the preamp signal.. i believe that is my problem.. i wired into the high level imputs.. and that signal is probably not high level.. I'm going to go try and wire the preamp signal into the RCA inputs now and it should be perfect..
Thanks for the help.. if i can figure out how to post images i'll post a pic when i'm done.

Speed-Racer

here's the link for my speaker install http://forums.corvetteforum.com/zero...=997508#997508

Speed-Racer

99HT

Adamg187

You are getting me worried. I am now lost to how you have your system wired. Please tell me you are using a fuse in the main power feed to the sub amp AND you put a 1 amp fuse in line with the "RADIO ON" signal from the HU to protect it. The RADIO ON signal should be used to control the remote power control input of the sub amp. Are you calling this the trigger input? The remote input of most sub amps draw very little power. Your radar detector should have nothing to do with your stereo system. The sub amp should get it's power from the battery with wire thick enough to handle it's power rating.

Adamg187

I have a 20 amp fuse on the main power feed.. i don't have a fuse for the trigger wire though.. i'm guessing i should add this. I'm using the radio on wire as my trigger. My radar detector was running on the radio on trigger also.. this was a bad idea because it was drawing too much current.. i disconnected that and need to find another trigger to wire the radar detector.

Here is the status on what i mentioned i would do about taking the low level inputs and connect them to the RCA input on the amp (instead of the high level input).

I hooked up the RCA low level from the preamp wires on the hU and the subwoofer sounded awesome, but there is a feedback problem and the rest of my speakers sounded aweful.. the rest of the speakers sounded like the headpiece of a telephone. I believe that the preamp signal ground i'm wired too is the wrong one. I'm wired to the light blue common ground (next too the Right Rear preamp wire). I believe that according to what 99HT mentioned above I need to use the bare wire next to the light blue wire as my ground for my preamp signal. Hopefully that will solve the problem I'm having with what i believe is the amp causing disturbance in the bose power amp loop.

Is this correct.... Help.

Speed-Racer

Speed-Racer

CCrane65

99HT, I have to disagree with you slightly about not taking the signal from the Bose amps in the doors. You do want to tap in there but tap into the feeder wires not the amplified wires. The feeders have gone through the Bose signal processor and so have the full frequency range and dynamic range available. I took that signal and fed it to a line level converter then into my amp via RCA jacks. There is absolutley no noise whatsoever and plenty of bass volume.

Point 2: there is a fantastic ground underneath the console cover. The driveshaft tunnel is all steel with welded studs protruding up from it for the nuts that hold the console cover on. There are at least 6 if not more studs to ground the amp to.

Adamg187

Speed-Racer.. you're saying I should have my signal ground go to the Radio ground wire.. but HT99 said above that the signal ground should be the bare wire on the C4 harness. I believe that if I ground the signal ground to the radio ground instead of the bare wire that I will be going against what HT99 said about keeping power loops and signal loops as sepparate as possible.. Please advise as too whether having a signal ground to the radio power ground is going to cause problems with the signal.

6SPEEDY

There are ground points at the back of the car also. There is a metal screw between the center and right rear compartment and another between the center and left rear compartment that hold the tub to the steel frame. Lift up the trim lining the compartments and you will see them. I use one for my amp and one for the 1/2 Farad monster cap I have . Works great.
Dave

99HT

Since the pre-amp outputs on the back of the HU are single ended and low impedance, it is best to pick off a signal for an external amp there. I did not do a proper reverse engineering of the BSP as I did of the HU to confirm this. When you tap the BSP, there is possibly a greater chance of causing a ground loop in the Bose pseudo-differential wiring scheme. It is also easier to tap the HU instead of opening the door or pulling down the BSP.

The BSP sums the signals from all the four inputs fed it before sending them too the two subs amps. There is no crossover in the BSP for the sub signals. Although this is a good idea to sum all the channels prior to extracing the sub info, most sub amps have two inputs already. It becomes somewhat redundant. The bass in the RF channel is no different than RR other than the setting of the fader.

99HT

Adamg187

There are many different ground connections on the HU. Never use the Common C4(13) LT BLU wire. This is used as the psuedo-differential return. You can use either use the Shield C4(14) Bare wire or Ground C4(15) BLK as your signal return. Technically the Ground C4(15) BLK is really a power return, but if you open up the HU you will see that they are connected to about the point in the unit.


The following are the Bose head unit 4 channel pre-amp outputs
Signal CD/Radio Color code
LF out C4(9) TAN/BLK
RF out C4(10) LT GRN/BLK
LR out C4(11) BRN
RR out C4(12) DK BLU
Common C4(13) LT BLU, DO NOT USE FOR EXTERNAL POWER AMP
Shield C4(14) Bare wire
Ground C4(15) BLK

CCrane65

Again I have to disagree with you. Having tried using the rear speaker wires to feed the subs, I found that there just wasn't the signal level required to feed the pre-amp inputs of the power amp. I had to use line level converters and tap the output wires going to the rear speakers. In reading the 2000 factory shop manual, it says that the signal for the rear speakers if first sent to the BSP then back to the hu and on to the speakers. In any case, I did not find the signal coming from the back of the hu for the rear speakers to be sufficient to drive my amp.