Gmt-900 Stereo Upgraded

Mattallica · October 27, 2009

Well I read a bunch of threads on this site and made some purchases a few months back.....finally got the time to install it all.

WOW...what an improvement over the stock system...I cant believe how much better it sounds now.

I would say that 1/3 volume now is louder than fully cranked stock....and 1/2 volume now is approaching 'stupid loud'....eventually I'll get the money up to put somes subs in the box I built...that ought to round it out.

I went with an Alpine MRP-F300 amp...2) Alpine SPS 600 in the front and 2) Infinity 6022i in the rear.Bought the Alpine stuff off ebay....gotta say it was a heck of a lot cheaper than the best buy prices?!?!?!

The wiring and routing took forever...and then the bad battery feed issue took an hour to figure out...but its all good now.

Definately going to try running all four corners off the rear channel...see if it sounds as good ....because the amplified turn and chime signals has to go.

2009 LTZ · October 27, 2009

Well I read a bunch of threads on this site and made some purchases a few months back.....finally got the time to install it all.
WOW...what an improvement over the stock system...I cant believe how much better it sounds now.

I would say that 1/3 volume now is louder than fully cranked stock....and 1/2 volume now is approaching 'stupid loud'....eventually I'll get the money up to put somes subs in the box I built...that ought to round it out.

I went with an Alpine MRP-F300 amp...2) Alpine SPS 600 in the front and 2) Infinity 6022i in the rear.Bought the Alpine stuff off ebay....gotta say it was a heck of a lot cheaper than the best buy prices?!?!?!

The wiring and routing took forever...and then the bad battery feed issue took an hour to figure out...but its all good now.

Definately going to try running all four corners off the rear channel...see if it sounds as good ....because the amplified turn and chime signals has to go.

Nice looking equipment. What did you use for the head unit? Did you keep the stock radio and add the Alpine AMP and speakers only? If so, how was the install and how did the AMP connect up?

Ron

Mattallica · October 28, 2009

stock head unit....used the GM pac connector...I forget the number...it supplies the plug and play connections for the rca outs to the amp..cost like $35...goes in behind the head unit,I ran the rca's out behind the upper glove box ,down the passenger side.

I think the whole set up cost me $400 with the wiring etc,..

2009 LTZ · October 28, 2009

Matt,

So everything still works - On-Star, Streering Wheel Controls, etc... So PAC connector to the stock Head Unit - RCA's from the PAC to the Alpine Amp? The new speakers in behind the existing door panel speaker openings, and the speaker wires running in the factory wiring from the Head unit or did they use the new PAC or AMP? Trying to figure out what goes in and out of the AMP. This sounds like a pretty nice solution to augment the stock head unit with much more power and better speakers... Was it really that simple other than hiding al of the wires and RCA cords? Where did you put the AMP and how did you power it?

Ron

Mattallica · October 29, 2009

Matt,

So everything still works - On-Star, Streering Wheel Controls, etc... So PAC connector to the stock Head Unit - RCA's from the PAC to the Alpine Amp? The new speakers in behind the existing door panel speaker openings, and the speaker wires running in the factory wiring from the Head unit or did they use the new PAC or AMP? Trying to figure out what goes in and out of the AMP. This sounds like a pretty nice solution to augment the stock head unit with much more power and better speakers... Was it really that simple other than hiding al of the wires and RCA cords? Where did you put the AMP and how did you power it?

Ron

Yes everything still works...the onstar,door chimes and blinkers are exceptionally loud however!

the quick cure is to only run the rear rcas and power all four channels/speakers of that signal...however the onstar wont work.

theres a thread about running a small speaker under the dash,out of sight and just hooking it up to the factory front left harness to retain onstar,etc,..that will be my next move.

the pac connector plugs into the back of the stock head unit...you unplug the 2 plugs from the head unit,plug in the adapter,plug the stock harness into the adapter.

The adapter has 2 sets of rca's(front/rear) and a signal wire for the amp....takes about 10-15 minutes to put in.

I removed the front speakers and used them to make a cardboard template so as to make a mdf bracket to put the new speakers in.(factory speakers are kinda pear shaped openings)...but you can buy adapter brackets for the speaker opening if you prefer.

I ran all new speaker wires to the four doors....1) because its heavier gauge 2) because you need to in order to run them from the amp channel outputs to the speakers.

the amp I mounted on the floor under the rear seat for now...eventually it will be on the back wall of the cab,behind the rear seat as others have done.

I bought an amp wiring kit by Scosche from walmart....came wit 16' of battery wire(8gauge?) and 16' of rca ,16' of signal wire,and 2-3' of ground wire(8gauge?)....I had to buy a 50' roll of speaker wire and an additional rca lead....all came to about $55.

the power wire ran down the driver side sill plates, up under the dash behind the e-brake ,out thru the factory wiring harness grommet,(which comes out next to the brake booster under the hood,)and then to the leftside terminal on the outside of the under hood fuse box.....dont use the right side terminal,which is smaller,because it doesn't supply constant battery power.

when you lift the cover off the fuse block you will see 2 terminal studs setting there on the leading edge of the housing...this worked perfectly for me and was just long enough to use the 16" supplied cable.

ap0352 · October 29, 2009

Lets us know if you try and run all channels off the rear outputs. I'm interested if the sound quality will change.

prioritypest · November 4, 2009

Lets us know if you try and run all channels off the rear outputs. I'm interested if the sound quality will change.

Sound qualty is the same, I installed all my stuff over the weekend. Wife hated the amplified chime and turn signal. Im running two amps so using the rears only is out of the question. I turned the gain down on The pac unit and its only slightly louder then before. Only issue I have is my JL 300/4 doesn't turn off somtimes

ap0352 · November 4, 2009

Couldn't you use something like a cleansweep and use only the rear channels for a signal?

prioritypest · November 4, 2009

Couldn't you use something like a cleansweep and use only the rear channels for a signal?

You could but then theres no onstar, phone or chimes. Mine is only slightly louder after I adjusted the gain on the pac unit

ap0352 · November 4, 2009

You don't have onstar as it is now correct? What happens when you try to add a sub? You'll need a pair of RCA's for that...

Seems like the little speaker under the dash is a must...

prioritypest · November 5, 2009

You don't have onstar as it is now correct? What happens when you try to add a sub? You'll need a pair of RCA's for that...
Seems like the little speaker under the dash is a must...

Haven't used the onstar, but have used the phone. Theres no reason the onstar wouldn't work the way it setup now. I have my 250.1 amp hooked up to the rear RCA's now. Fronts hooked up to a JL 300.4 briged to alpine components in the doors. Like I said the chime is a little louder the way its setup now. When I get over the flu I'll screw with the gains on the amp, currently turned all the way down but at half volume its already loud enough for me. Damn alpine tweeters our to bright.

bluemonstercali · November 5, 2009

i just installed my set-up. similar to yours but i used a clean sweep. the cleansweep has its own gain nob which i used to keep the chimes at around the same loudness as stock. and still the system gets plenty loud. i went with Boston pro 60 upfront, diamond audio for the rear, and a image dynamic sub. 1 massive audio amp for the sub 2x400 at 4ohms but i think it's wired at 1x 800. and a 4x800 for the door speakers. system sounds clean and tight. tweets are a bit bright but overall awesome. and best part is you can't tell that there is a system

DofD · November 5, 2009

Congrats on the new system. It doesn't take much to improve on the new system. I used a RF 3Sixty.2 in my upgrade. The chimes, etc are louder but intolerably so. It's just tuning things properly issue. I used Boston Pro 60's front and rear, a Stealth Box, and two JL HD600's to power everything.

bluemonstercali · November 5, 2009

are your tweets bright aswell?

ap0352 · November 5, 2009

Congrats on the new system. It doesn't take much to improve on the new system. I used a RF 3Sixty.2 in my upgrade. The chimes, etc are louder but intolerably so. It's just tuning things properly issue. I used Boston Pro 60's front and rear, a Stealth Box, and two JL HD600's to power everything.

Damn!! Those HD's are nice!! How do you like them?