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02/Factory AMP Bypass-A Simple Fix/great Results

I double checked everything, and they wired it properly. Maybe I just wasn't sure what to expect from this magical bypass. It is the stock HU, and stock speakers. I'll probably just keept it where it is. The sound really is good. I think I set my expectations a bit too high, that's all. Like someone said long ago towards the beginning of this thread...if I want $1000 sound, then trash the stock system and start from scratch. It's all good. It sounds far better than before, at least with a bit more bass coming from the BL. I just have to turn down the treble a touch to keep from overdriving my ears with high frequency. Thanks for the suggestions!
 
Lots of discussion around bypassing the factory "amp".

There's a volume compensation system described in my 02 owners manual. Apparently it increases the volume at higher speeds to account for road noise. I never really used it or noticed a benefit. I've also noticed that cranking the stereo can actually reduce the volume which seems strange.

Could this factory "amp" have anything to do with the volume compensation system.

Just a thought...
 
avalanchefan2 said:
Lots of discussion around bypassing the factory "amp".

There's a volume compensation system described in my 02 owners manual. Apparently it increases the volume at higher speeds to account for road noise. I never really used it or noticed a benefit. I've also noticed that cranking the stereo can actually reduce the volume which seems strange.

Could this factory "amp" have anything to do with the volume compensation system.

Just a thought...

not on mine.....it still goes up and down with speed......I think that is all in the radio.......

I love the speed controll....I find myself adjusting volume less...even though I added the steering wheel controls to my 2002....THANKS JP CUSTOMS.....hehehehe
 
avalanchefan2 said:
There's a volume compensation system described in my 02 owners manual. Apparently it increases the volume at higher speeds to account for road noise. I never really used it or noticed a benefit.
If it's working properly, and you have the SCV control (which is the lever behind the volume control) set right, you shouldn't even notice it's there. >:D

If it's set too low, the radio will get drowned out by road noise, and it will actually seem to get quieter as you go faster. But if you have it set right, the radio will get louder as the speed goes up, and it will not appear to have changed at all.

I have grown quite dependedant on this feature. I love it. (y)

I've also noticed that cranking the stereo can actually reduce the volume which seems strange.
The amp bypass seems to help this wierd problem.

Could this factory "amp" have anything to do with the volume compensation system.
Possible (as there is a gain signal between the radio and amplifier) but highly unlikely. I have the amp bypassed, and the speed controlled volume still works just fine.

-- SS
 
GMcNair.....what you described by your bass being better if faded either left or right but not center is a common mistake that was made. It sounds like your system is wired out of phase. If your speakers are not ALL wired with the positive to positive and negative to negative then you will have a "cancelation" of bass. By fading to one side and having more bass, you already did the test to find out if this "phase cancelation" is happening. Have them go back and look to see if they have your wiring done correctly and see if that fixes your problem. Sometimes on my PA setup this happens and it is an easy mistake to make.

Just an idea, and hope that helps.

Wiki
 
Just finished the bypass on the AV and I must say "Thank you all".

With the Alpine pushing my AVI fronts and Directed rears running through the factory amp I noticed distortation. After doing the bypass I can crank them puppies up and really enjoy them. Didnt even bother tossing in an amp cause there was no need.

Tip on the factory plugs going into the amp. That big black bugger blocks access to yank the plugs. After a little over 2 weeks of frustration I took another look and guess what. The factory amp can be pushed in towards the engine then up and pops right out for easy access. FYI for those like me that have big gorilla fingers.


BusterAv
2002 Indigo 2500
 
I am trying to decide what to do, the speakers in the right front door need replacing, I bought a set of Eclipse 6.5 coax 3 ways. I installed right side and disabled tweeter, it actually sounds worse than the stock left side (no bass).

Could this be do to the factory amp?

I have non bose oem HU, onstar. Does bypassing the factory amp effect onstar? ( which I have not subscribed to for 1.5 years).

I have also thought about adding a new headunit that is XM ready, but am concerned as some posts I have read say this can effect airbags, chimes, and onstar etc.
I am not to worried about onstar, can do the bypass or PAC-OS-1.

I bought an aftermarket unit for my other truck and installed it in the Av. just to try it -it had no sound. Also on OEM radio if you unplug 9 pin harness= no sound. I assume the onstar bypass with small speaker would fix this.

Option =

oem HU + xm tuner +xm antenna + pie gm9-aux

new HU xm ready+xm tuner+xm antenna+pac os-1 OR onstar bypass
 
flare said:
I installed right side and disabled tweeter, it actually sounds worse than the stock left side (no bass).
Maybe it's out of phase? Try reversing the polarity of the connections on one side. Other than that, all I can offer is to double and triple check connections. I'll defer this one to an audio guru. Anyone?

I have non bose oem HU, onstar. Does bypassing the factory amp effect onstar?
I've done the factory amp bypass, and it truly has no effect on OnStar. Everything that used to work, still does. It just sounds better now.

I have also thought about adding a new headunit that is XM ready, but am concerned as some posts I have read say this can effect airbags, chimes, and onstar etc. I am not to worried about onstar, can do the bypass or PAC-OS-1.
Your signature indicates that you have an '02. The chime/airbag concerns only apply to '03 and later from what I hear. Yes, replacing the HU will disable OnStar, but the PAC-OS-1 takes care of that.

I bought an aftermarket unit for my other truck and installed it in the Av. just to try it -it had no sound. Also on OEM radio if you unplug 9 pin harness= no sound. I assume the onstar bypass with small speaker would fix this.
How were you hooking up the speakers? If you were hooking them up to the stock speaker wires that attach to the stock radio, it might just be that the stock amplifier was not turned on.

The speaker outputs from the stock radio go to the stock amplifier and then on to the speakers. There is a line from the radio to the amplifier that is needed to turn the amplifier on. If this signal was not on, then you may not get anything feeding through the amp.

This could explain both your problems. When you put in your aftermarket HU, you probably didn't hook up the "amplifier on" signal. Same thing when you pulled the nin pine plug: the "amplifier on" signal routes through that plug.

If this is the case, you have two options:
  • run new (good quality) speaker wires directly to the doors (really, the best option if you are doing a full HU/speaker retrofit)
  • do the amplifer bypass so that it is out of the loop and does not need to be turned on.
Option =

oem HU + xm tuner +xm antenna + pie gm9-aux
This is an option, and it will work. I have done the same, except that I added an mp3 player instead of the xm tuner/antenna. If you go this route, I would recommend you do the amp bypass. It really improved things when I did it. It won't turn it into an audiophile quality system, but it will change it from a really crappy stock system to an average stock system.

new HU xm ready+xm tuner+xm antenna+pac os-1 OR onstar bypass
This will sound better, especially if you put in new speakers and new speaker wiring. If you don't susbscribe to OnStar, there is really no need for the PAC-OS-1. As for the onstar bypass, I don't really know what that is. Do you mean the factory amp bypass? If so, it has nothing to do with OnStar.

If you put in a new HU, and don't subscribe to OnStar, then you should probably just wire up everything from scratch. Just leave the factory amp and OnStar units in place and disconnected, and they shouldn't hurt anything. (I don't speak from experience on this, I still have the factory HU and an active OnStar subscription. All I have done is the PIE aux inputs and factory amp bypass.)

I'm sure there is someone here who has done exactly that, and can indepentantly confirm this.

-- SS
 
Thanks SS. I have tried reversing polarity on the speaker and it dosnt seem to make much difference. The stock speakers seem to have to much bass and may give the impression of not enough bass in a quality aftermarket speaker as well as the stock amp not being bypassed. I may leave the door panel off and go back to the Audio store and try some other speakers to compare. Any recommemations on good speakers?

I did hook up the aftermarket HU using the stock wire harness and matching adapter. It now makes sense about the wire that turns on the stock amp, it was disconnected (9 pin harness wasnt hooked up) I will do the amp bypass with the metra 70-2002.

The onstar bypass I mentioned is what I found on another thread, you connect the "amp on" wire from the 20 pin harness to the #7 pink wire in the 9 pin harness and then add a small speaker to #10+#11 and #12 wires in the 9 pin harness, you now have onstar working through the small speaker instead of the main speakers ( just the cheap way so you dont have to buy the Pac-os-1)

For curiosity I may try this: unplug the 9 pin harness from the stock HU and do the above connections, leave it unplugged and see if this turns on stock amp and if little CB speaker works for onstar ( Iam not subscibed but get an intro when I push the blue onstar button) it should work. Basically this should be the same as installing an aftermarket HU, using stock wire harness with adapter to new HU, and using stock amp with a poor man Pac-os-1. Like I said just for curiosity until I can get a Metra 70-2202 and bypass that stock amp either with a new HU or stock HU and the new speakers.
 
flare said:
The stock speakers seem to have to much bass and may give the impression of not enough bass in a quality aftermarket speaker as well as the stock amp not being bypassed.
That's the stock amp giving the impression of "too much" bass. You could also describe it as "heavy" and "muddy" aslo. :9:

But personally, I think the problem is more that there is not enough treble (see my diatribe below about the amp.) At first it sounds horrible, but then your ear gets trained to it. Once you get used to the boomyness, anything else sounds tinny. :p

flare said:
I may leave the door panel off and go back to the Audio store and try some other speakers to compare. Any recommemations on good speakers?
I don't have any speaker recomendations. The last time I bought speakers was 20 years ago. When my soon-to-be wife was buying a Celebrity Eurosport, I talked her into getting it with the radio deleted. I then put in a full-blown Alpine system (HU, EQ, front/rear amps, dash/door*4/rear deck speakers.) No a show quality system, but it did blow the doors off anything that you could get from the factory. That was 20 years ago, and now being an old married f*rt, I haven't put in complete stereo since. :6:

I'm sure someone else will come up with speaker recommendations. I haven't looked at them in a while, but I do recall that there were a lot of discussion about the pros/cons of various speakers.

I did hook up the aftermarket HU using the stock wire harness and matching adapter. It now makes sense about the wire that turns on the stock amp, it was disconnected (9 pin harness wasn't hooked up) I will do the amp bypass with the metra 70-2002.
That is worth a try. If nothing else, the bypass will give you a cleaner sound without that stupid amp trying to mess up the equalization. Do the amp bypass before you go testing new speakers.

I don't know why they put that amp in the Av. All I can think of is that it is an equalization device and crossover for the Suburban/Tahoe, which splits up the signal between a bunch of different speakers: in the A pillars, the doors, the back cargo area, and the rear window door pillars. I think they may be trying to put the non-directional low frequencies in the doors, and put the higher frequencies in the pillars where you get better stereo imaging. The only problem is that in the Av they left off all of the high frequency speakers! (The tweeters in the door don't count if all that is being fed into the doors in the first place is bass!)

Maybe with all the extra speakers the amp/crossover makes sense, but in the Av all it does is hurt the sound quality (what ever little there is to begin with.) :6:

The onstar bypass I mentioned is what I found on another thread, you connect the "amp on" wire from the 20 pin harness to the #7 pink wire in the 9 pin harness and then add a small speaker to #10+#11 and #12 wires in the 9 pin harness, you now have onstar working through the small speaker instead of the main speakers ( just the cheap way so you dont have to buy the Pac-os-1)
Sounds interesting. I missed that one, got a link? I'd like to compare it to my shop manual wiring diagrams and try to figure out what it does.

Good luck with your upgrade, sounds like you have some fun experimentation ahead of you. (y)

-- SS
 
SS the link is in the above post, didnt really know how to do a link but it worked.
 
flare said:
SS the link is in the above post, didnt really know how to do a link but it worked.
Yep, it worked. (y)

OK, now that I see it, I do recall seeing it in the past. I will have to get the service manual out and see what is really happening.

I think what is going on is that when OnStar wants to use the radio, it sends a serial command to the radio telling the radio to switch to the aux inputs. It then sends sound into the radio using the aux inputs. On the surface, it seems like this bypass is really just disconnecting OnStar from everything, the serial data is ignored, and the OnStar audio goes to its own amp/speaker. The real work seems to be bypassing the turn on signal for the remote amp so that it still works. But I will confirm this whan I have time. (not now.)

It seems that this is built on two suppositions: that OnStar will work just fine without getting any serial data feedback from the Radio (it might just set a diagnostic code but still work) and that there is no noise on the audio lines from OnStar when it is not talking.

Makes me wonder what the PAC-OS-1 really does? Maybe all it is, is an amplifier to power the external speaker so you don't need an amplified speaker? But if I recall, I think it also has an entertainment mute output so it mutes the radio while a call is happening. It don't think this bypass idea will do that. The last thing the PAC-OS-1 might do is send back serial messages as if it were a radio so that OnStar doesn't complain about no radio being there and set a code. I don't know.

This is interesting, I'll have to do some more reserarch on this. However, since it doesn't affect me directly at this point, I think it will have to wait a bit before I get to it.

Thanks for bringing this up and for posting this link. I wish you luck in getting your setup working to your satisfaction. (y)

-- SS
 
In a previous post I said that the Eclipse speaker I had installed in the front right door didnt have as much bass as the left front oem speaker, well today I made sure it was phased correctly (because it actually wasnt),I reinstalled the door panel, and shut the doors and listened- the Eclipse is not quite as bassy but definately sounds a lot better than the left oem. Then I did the Metra 70-2002 amp bypass and installed the leftside front Eclipse, the bass seems to be good now and sounds much cleaner. The back speakers are oem and do seem to have a little more bass than the front but do not sound as clear, I guess I will have to change them too.

I also played with the 9 pin connecter on the back of the HU (before I did the above), I unplugged it and jumped the pink #7 wire to the ignition switched wire on the HU (dark green) and yes it did turn on the factory amp and allow sound to speakers (this would be important if you installed a new HU and NOT a pac-os-1 and kept using factory amp because the 9 pin harness would be left just hanging there=no sound because amp dosent get turned on).

I also hooked up a small unamplified speaker to wires #10+#11 and #12 from the disconnected 9 pin harness. Then I pushed onstar button and I could here the intro but very quiet- you must use an amplified speaker. So it does work but you are correct in that it does not mute the stereo.

Now all I have to do is decide if I want to add a new HU that is Xm ready or use the stock HU with the PIE gm9-aux. If I do get a new HU I may just leave onstar disconnected for now as I dont want to buy the PAC os-1 right now and I feel it is better than the bypass with amplified speaker. I am not subscibed to onstar right now.

I am going to Missoula Montana this weekend so I will look at XM units while there, as you may know they dont sell them in Canada ( our government wants to control what we watch and listen to). I know others in Canada are using XM and it works a lot further North than I live. Just a few hoops to jump through to get XM and I think I have that figured out. Thanks for your help.
 
timcosco said:
The amp I ordered is a 4 channel, 300W unit from Pyramid (PB251). I chose it because it appears as if it will fit in the stock "amp" location when mounted vertically (it may require some custom brackets though) and with such a low price, I won't be out much if/when it comes time to replace it. It has speaker level inputs, so I think I'll just connect the stock H.U. directly to those. My thinking was to get good speakers first and worry about a nice amp later... and a groovy aftermarket head unit sometime after that. I'm fairly certain this first upgrade will be a general improvement over stock.


Above was response #43

Can you tell us how this worked out? I am very happy with new HU + speakers + bypass. I thought it would be a simple upgrade if I could find a 4 channel amp that would actually fit behind the glove box where the OE amp was.

ANY information you can provide would be greatly appreaciated. I read all 7 pages of this topic and did not find any additional feedback.

THANK YOU!
 
hello everyone all this tech over a radio swap what is gm thinking............. any way i have some very stupid question

i have a 2002 av with on star
i have new HU pioneer deh-860mp
i connected the pink wire from 9 plug to system control blue wire from new HU
i want to bypass amp but i'm not understanding what :E: excatly am i doing this metra plug what do i do with the wires? i looked at the picture is it easier to get metra plug on just t tap as in picture ???
 
Has anyone mounted an aftermarket AMP where the stock one is behind the glove box? My Av has no bose, no amp, no On-Star. I have a Blaupunkt San Jose and some Pioneer 6.5 3 ways in the front and back. I can't crank it like I want. I was thinking of adding a small 4 channel amp something in the neighborhood of 50 RMS- per channel to 'wake' it up. The Blau has sub outs, so in the future I will want to put a sub in, but I carry to much stuff in my AV to lose space under the rear seats....my Sirius Tuner is already back there!
 
Droopie said:
Has anyone mounted an aftermarket AMP where the stock one is behind the glove box?
I had considered it, and dismissed it. There is not a lot of room there (about the size of a medium-large paperback book) and it is a really cumbersome place to try and reach. I'm sure it can be done, but you won't fit a very large amp there, and it will not be easy.

-- SS
 
Here's some prints for reference.

Click the pic or link to expand them. (Depends on your browser.)
 

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Wow. There really is a difference between bass and a muffled sound.

This mod did make a difference. Sounds better. Even with stock HU and speakers.

However, trying to undo plugs from 'amp', was a PITA!!!!!
It took me longer to unplug the d@nm thing, than to reconfigure and solder/shrink wrap the new plug.

Thanks, to everyone that contributed to this mod.  :love:  :love:  :love:  :love:
 
Ok guys I just ordered the metra harness from crutchfield so I can by pass my factory amp and finally use my $400 alpine head unit with out paying another $100 for a harness. I will let you guys know how it turns out if I can figuire it out. Before the headunit was getting power but no sound so it looks to be the factory amp is the culprit from what you guys have said.

Alex
 
I am still kind of lost here, so I plug the metra harness into the factory harness that plugs into the top of the amp then exactly where am I splicing the metra wires into?
 
02_2500avalanche said:
I am still kind of lost here, so I plug the metra harness into the factory harness that plugs into the top of the amp then exactly where am I splicing the metra wires into?
each other....

it goes from one pin of the plug back into aonther pin .....
 
It will (could) look like this...

542983_180_full.jpg
The Factory IN/OUT plug disconnected from the Factory "Amp"

542983_183_full.jpg
The METRA By-Pass installed on the Factory IN/OUT plug

Murman :cool:
 
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