[chrstphr81620]

The rear door speakers are supposed to be subwoofers, they are referred to as such in the FSM.... WHen they are working the way the factory intended, they won't produce anything but low base.... I'm not saying it's the best way, but it's GM's way.... I never tried it, but I imagine if you ran a complete signal to them, they wouldn't sound very good in the upper ranges....

Not sure why they did it this way, or what their logic was, but after this by-pass I seem to have full range in the door speakers and it sounds just fine. I'm considering getting a new set of real speakers (not "subs") for the rears, but funds are going to the 100+ other projects I have going on. Not sure if there are any tech specs the recommend doing anything differently.

 

[paulo57509]

Just a guess here, but in order to get the factory amp to work it probably needs to have a line level converter put in between the head unit speaker output and the amp input:



Or if the head unit already has low level outputs (RCA jacks), connect these to the amp.

 

[esc]

I'm a little confused.
If the amp is getting a signal that is split off of the center speakers, wouldn't that signal have already been amplified, not line level?
If it got a high level input in the first place why doesn't it just work?
I feel like there is some important piece of information missing in this puzzle.

Why does the factory amp stop working in the first place?

 

[chrstphr81620]

Just a guess here, but in order to get the factory amp to work it probably needs to have a line level converter put in between the head unit speaker output and the amp input:



Or if the head unit already has low level outputs (RCA jacks), connect these to the amp.

This would work if you wanted to swap the Stock Amp with an Aftermarket one. - The Factory amp doesn't have RCA inputs.

EDIT: Nevermind, I see what you mean. This could very likely work. But only worth doing if you have one laying around. (Why spend money when there's a way to do it for free?)

 

[chrstphr81620]

I'm a little confused.
If the amp is getting a signal that is split off of the center speakers, wouldn't that signal have already been amplified, not line level?
If it got a high level input in the first place why doesn't it just work?
I feel like there is some important piece of information missing in this puzzle.

Why does the factory amp stop working in the first place?

My only guess: And this could be way off.

The Stock Head unit doesn't have the power to supply the 4 Rear speakers in in the Back. So the head unit supplies what it has to the amp and the amp "boosts" the power to the rear (door) speakers.
- Interesting fact: IF you unplugged the amp, the back 4x6 tower speakers still work.

Which means, the main power is being run to the back Tower -at some point it Splits - Goes to the amp - then runs to the rear door.

My suspicion, is that since your Aftermarket HU is powered by an internal amp, there is TOO MUCH juice running into the amp and it just decides to stop working.

OR

The Metra wiring harness (Which seems to be the only one available) Doesn't include the Amp (Turn-on) power. A solution could be as easy as hooking up a power supply to the factory amp. I considered this, but didn't want to run into an issue involving too much power from having two amps. This would be an easy test with a volt meter, but I had already started doing the wire-bypass and it wouldn't have changed my process.

If someone does this process, and wants to see if the Turn-On wire for the factory amp has power, I'd love to hear what the results are.

 

[esc]

My only guess: And this could be way off.

The Metra wiring harness (Which seems to be the only one available) Doesn't include the Amp (Turn-on) power. A solution could be as easy as hooking up a power supply to the factory amp. I considered this, but didn't want to run into an issue involving too much power from having two amps. This would be an easy test with a volt meter, but I had already started doing the wire-bypass and it wouldn't have changed my process.

If someone does this process, and wants to see if the Turn-On wire for the factory amp has power, I'd love to hear what the results are.

This gets my vote. As soon as I have time I plan on looking into it. I need to take a closer look at the wiring diagram you provided early in this thread. If it identifies a power switch of the amp, I may just see if any wires the Metra harness (or whatever I find in my dash) isn't using have continuity with that wire.

Edit: I took a closer look and it seems to just have a one positive power wire. There must be a relay somewhere. I'll at least check to see if it has voltage. If it doesn't I'll run some to it temporarily just to see what happens.

 

[esc]

I went out to my van today and pulled the side panel off. After removing two screws in the door jamb, it came off just as easily as described in the first post.

I tried a couple of things:

First listening to rear door speakers before and after unplugging the amp. There was a definite loss of bass sound when the amp was unplugged. The amp may not be doing all that could be hoped, but it is doing enough to be noticed.

Next I took a multi-meter to the plug and discovered that both the positive and ground are always on. It doesn't make any difference where the key is or is not located. This caught me by surprise. It was not what I was expecting.

I now have two new guesses:

First, the amp must turn it's self on when it detects voltage on the rear speaker wires coming from the head unit. Those are the only other wires going into it and if it didn't turn it's self off somehow, it would drain the battery.

Second, I'm starting to wonder if maybe after market head units might have some soft of low filter. That would filter out most of what the factory amp is trying to amplify.

I think that a better description of what the amp is supposed to do is needed.

BTW, does anyone know what the impedance of the factory speakers is? Are they 4 ohms, like almost all car speakers, or something wacky like sometimes get used by manufacturers?

 

[biker80]

The rear speakers are spec'd at 3 ohms. Only bad thing with just bypassing the stock amp is the impedance doubles being drawn for the rear channel. That can cause a quick death of an aftermarket HU. The amp and rear speakers worked fine in mine after changing the HU, I changed to a aftermarket amp for the door speakers for tailgating and just had to run a remote trigger wire back to it. I also cut my doors out a bit and installed a set of 3 way 6x9's.

 

[esc]

OK, 3 ohms is [Edit]isn't[/Edit] that wacky.
Did you use an amp with a speaker lever input?

 

[biker80]

Yes, only wish it had been small enough to fit into the stock area. I used a cheap 400 watt Dual from Walmart.

 

[chrstphr81620]

The rear speakers are spec'd at 3 ohms. Only bad thing with just bypassing the stock amp is the impedance doubles being drawn for the rear channel. That can cause a quick death of an aftermarket HU. The amp and rear speakers worked fine in mine after changing the HU, I changed to a aftermarket amp for the door speakers for tailgating and just had to run a remote trigger wire back to it. I also cut my doors out a bit and installed a set of 3 way 6x9's.

My HU specs are 4-8 ohms, So I did a bit if research to see how compatible that is for 3ohms. Biker80, let me know if you disagree, I'm just relying on what the internet tells me (So you know it's all correct) A few sites I've visited have pretty similar answers. But I'm still considering getting a set of 4-8ohm speakers to be safe.

Taken From Another Site: http://www.sonicownersforum.com/forum/i ... m-amp.html \/ \/ \/ \/ \/ \/

This may make you feel a bit better.

2 ohms, 4 ohms, 8 ohms is a nominal measurement. an 8 ohm speaker may dip as low as 4 ohms at certain frequencies and may go up to 15+ ohms at other frequencies.

That so called '8 ohm speaker' can look like anything from 4 to 15+ ohms to the amplifier especially if a passive crossover is used.

Point is, that 3 ohm speaker will almost never look like 3 ohms to the amplifier so its really no different then a 2 ohm or 4 ohm nominal speaker. Its just a general guide and as sonic007 said it will be fine. If the amplifier was running borderline hot to begin with it may cause a problem but that shouldn't be the case.

Overall a 2 ohm speaker looks like a lower impedance then a 4 ohm and that 3 ohm will appear slightly lower then a 4 ohm but nothing will care.

This may give you an idea of what I'm talking about.

/\/\/\/\/\/\/\/\/\/\

Full disclosure: I have no idea what that graph says [\b]

 

[chrstphr81620]

Sooo After a bit more research,

I found THIS!

It's hard to read, but it's the full wiring diagram for our van.

Good news! This means that our 4ohm rear Tower speakers and our rear 3ohm "subs" are wired in a series after doing the factory amp bypass. Meaning, we're creating a Total Impedance of 7 Ω per channel. (Thanks to this handy calculator: http://www.speakerimpedance.co.uk/?act= ... calculator)

So a common 4-8ohm aftermarket HU should have NO issues powering our rear speakers, and you shouldn't encounter impedance issues after this mod.

--- This is just my judgment after reading the diagram and drawing in the mod on my own. Please let me know if I've made any mistakes.

 

[esc]

Nice!

Where did you find that?
A complete wiring diagram it may be useful for who knows what else.

 

[biker80]

Understood and you are right, mainly a issue for those that listen at the stereos limits most of the time anyway, just being cautious.

 

[Broseph]

Thanks for the post. Having that wiring info made it sooo easy to bypass the factory amp! I removed all the stock stereo equipment and replaced. I put an amp under my new deck above the dog house. Instead of a plastic shelf replacement for the factory cd player I built a custom wooden shelf enclosure. While I was in there I also tackled an air hose problem, but that's for a different post!

Stereo

• Broseph
• Jan 20, 2017

After market stereo deck and custom shelf enclosure unit

factory amp wiring

• Broseph
• Jan 20, 2017

Bypassed factory amp

 

[WimpTech]

Good work Broseph. Might wanna cap that orange, those are usually hot all the time.

 

[chrstphr81620]

Thanks for the post. Having that wiring info made it sooo easy to bypass the factory amp! I removed all the stock stereo equipment and replaced. I put an amp under my new deck above the dog house. Instead of a plastic shelf replacement for the factory cd player I built a custom wooden shelf enclosure. While I was in there I also tackled an air hose problem, but that's for a different post!

Stereo

• Broseph
• Jan 20, 2017

After market stereo deck and custom shelf enclosure unit

factory amp wiring

• Broseph
• Jan 20, 2017

Bypassed factory amp

Hell yeah! Nice work. Glad my instructions worked!

 

[Broseph]

I am actually going to put a rear speaker amp back in that spot, but it will have to wait....

Wimpazz....I capped two wires I think, I just got photo-journalistic before I finished my work!

 

[chrstphr81620]

I am actually going to put a rear speaker amp back in that spot, but it will have to wait....

I put my aftermarket Sub Amp in that spot, and wired in my 12" Sub. Sounds great!

 

[Bigfoot]

Thanks for the post. Having that wiring info made it sooo easy to bypass the factory amp! I removed all the stock stereo equipment and replaced. I put an amp under my new deck above the dog house. Instead of a plastic shelf replacement for the factory cd player I built a custom wooden shelf enclosure. While I was in there I also tackled an air hose problem, but that's for a different post!

Stereo

• Broseph
• Jan 20, 2017

After market stereo deck and custom shelf enclosure unit

factory amp wiring

• Broseph
• Jan 20, 2017

Bypassed factory amp

That sounds like a great place for a amp! Think you could post a picture of how you have it tucked up in there?

I've been trying to figure out a mounting location for mine. I'm going to put my sub amp where the factory amp was. Been trying to figure out where to put my 4 channel. My goal is stealth and space saving. Not going to be able to see any added bits besides the headunit and I'll retain all my storage space.