M&T Factory amp

[NickTrahan]

Hi guys, I'm a long time reader, first time poster. Anyway, I have an 03 Vibe base with the single disk M&T pkg. I just decided to upgrade the sound, so I got the install done at a local shop. When I got the car back the installer says he had to disable the factory amp to properly hook up the HU. This guy also owns an 03 vibe so I assumed he knew what he was talking about. Well, my problem is now I have no mid-bass in my system at all. The highs sound great and so does the sub-bass, but theres no middle ground. So my queestion is, did this guy know his stuff? Is there a way to reconnect the factory amp, I liked the way the factory system sounded, I just wanted more punch.

[joatmon]

The audio gurus here say that the door speakers that come with the M&T package are 2 Ohm , while the door speakers that come in Vibes without the amp are 4 Ohms, maybe that is related to the problem you are having. The factory amp is set up to drive 2 ohm speakers, the new headunit probably is not. Either that or perhaps whatever he did to tie in the tweeters isn't quite right.seems like many people have replaced the head unit and kept the factory amp, I think some people used some sort of level converterHow did you do in the big hurricanes last year?

[NickTrahan]

Hey thanks for the quick reply. I'll do some research into that level converter then give the guys at the shop a call. I really miss my mid bass! About the hurricanes, well Katrina didn't do much of anything to my house, but Rita wiped it totally off the map (including my new 330Ci). I lived in Houma then so I moved a little north to Gonzales (a suburb of Baton Rouge). I'm planning on moving back to TX soon so I can totaly avoid these hurricanes.

[joatmon]

There's a bunch of threads here about new headunits with the factory amp, although it may take some digging with the search tool to find them.sorry about the house, but at least you're ok. things can be replaced, people can't

[NickTrahan]

I dug up some info about the Scosche FAI-3A. I just ordered one from cardomain so when it gets here I'll see how it goes, it looks like a winner. Thanks for the help.

[joatmon]

I think the line converter is needed to adjust the signals from an aftermarket headunit to the factory amp. If the installer bypassed the factory amp, and you leave it bypassed, the line converter is probably not going to be useful. If you restore the factory amp, then I don't know how much more power you'll get out of the aftermarket headunit than you did from the stock one. Hopefully one of the audio gurus (an elite club I don't qualify for ) will chime in.

[NickTrahan]

Ok, after some thinking (and getting a great deal from my installer) I decided to just skip the factory system altogether and upgrade to Polk Audio db6500 componets up front, Polk db650 2-ways in the rear and a Polk MOMO C400.4 amp to power it all. At $493 I think it would be worth it, considering what I just paid for the bass package. I might as well go ahead and get some quility speakers. So, now that the sound's going to be taken care of, I guess its time to convince my dealer head that installing the supercharger and sport pkg on my car will help move the vibes off our lot!

[dbiehl1979]

I think that you will be happy with the results. my adventure sarted when i bought an alpine hu with mp3 capability. BB tied it into the factory M&T amp but i cant turn it up above 5 without blowing my ears and speakers. the sound was just horrible. I then decide to jump in with both feet and get the same polks that you stated and an alpine 4 ch amp. 17 hours and one VERY clean install later, i found out about the scoche (sp?) adaptor. well, im happy with the sound quality so im not to worried about the price difference. Since ive added another 2 ch apline amp driving an 10in polk in the back and an alpine 6 disk changer. right now ive got the fever for a car pc that im trying to fight off.

[NickTrahan]

I know how you feel about the CarPC. I was thinking about on too, utill I found this: http://www.alpine-usa.com/en/p...-W200It does every thing I wanted in a CarPC, and with MUCH less hassle. I couldn't be happier

[Jahntassa]

CarPCs can be a bit of a hassle, but they're really fun to tinker with.If you want something that's easy to use and cool, get the Alpine. If you want annoyance and fun of doing it yourself and doing really cool things, try a CarPC. But if you CAN'T deal with the annoyance of computers and such, then get the Alpine.

[NickTrahan]

Quote, originally posted by Jahntassa »CarPCs can be a bit of a hassle, but they're really fun to tinker with.True, but I no longer have much spare time between work and taking care of my little sisters, so the Alpine gave me most of the functionality I wanted with the least amount of work. Some buddies of mine have done some awsome things with their CarPC's though.

[DHelm72]

If the speakers with the Monson system are 2 ohm and you just replace them with 4 or 8 ohm speakers it should work. The only problem is that you would get about half of the power out of that amp using 4 ohm speakers and 1/4 using 8 ohm speakers. If the amp is 2 ohm stable, which it must be if the door speakers are 2 ohm then you can replace the door speakers with 2 ohm speakers and get the same power out of the amp. TThe problem with factory amps is that they probably have a built in crossover in the amp or before the speakers somewhere. If you simply replace the speakers you will have only midrange to the lower door speakers and highs to the tweeters if you don't bypass the crossover. If the crossover is in the amp then you have to bypass the amp.The amp is also probably supplied with signal level inputs with a factory gm plug rather than RCA cables. You can't provide line level input from an aftermarket head unit to the factory amp with RCA cables because the factory amp probably has no RCA input. If the factory amp uses speaker level inputs then you could use the speaker level inputs from the head unit to the factory amp but the input sensitivity would not be adjustable on the amp. If the input voltage isn't matched just right to the amp you will get all kinds of distortion. I presume the factory amp has no gain (input level) adjustment because it is matched exactly to the input level from the factory radio so you will have massive distortion which ever route you choose from an aftermarket radio wired to your factory amp.This is why your installer had to bypass the factory amp.

[DHelm72]

Sorry, I forgot to answer your question about your lack of midrange. I assume you have no amp now, and are running strictly off the head unit's power. You mentioned no amp. You should have full range to the speakers if you are running straight from the head unit. If the installer bypassed your factory amp but did not run new wires from the head unit to the new speakers you may have a factory crossover somewhere in the doors or behind the dash or somewhere. This could be your problem. If you have all new speaker wires run from your head unit (which he should have done if he bypassed the factory amp) then I don't know why you are missing midrange. Did you buy midrange/tweeter separates or did you buy 2 way speakers?If they are 2 way speakers, you just run from the head unit straight to the speakers and the speakers have an internal crossover. If you have separates, the speakers come with a crossover that the installer hides somewhere. Either way, the speakers should have full range run to them through the crossover. If you are running a subwoofer as well you should run mid/high to the separates and low frequency to the sub. You will need a separate crossover or an amp/amps with built in adjustable crossovers. There are too many ways to wire the system to tell you all of them but I can think of just a few reasons that I have mentioned above why you may have lost your midrange frequencies when you added a new head unit and speakers and bypassed the factory amp.

[AJ_'04 Vibe]

My guess is by hooking up the factory speakers to the aftermarket HU, he may have flipped some of the wires around and the two doors are running out of phase.Or they simply could be out of phase with the sub. Was a crossover used for the sub? If so, and the factory speakers are supplying the only mid-bass, having them out of phase would cause the exact problem you're having.If there is no crossover on the sub, then having the sub out of phase with the front speakers can cause the same thing.Or the rear doors (if they're still being used) are out of phase with the front doors.... etc., etc.Speaker phase is very important. Get it wrong and you'll know it.BTW, I hooked my aftermarket HU straight to the factory amp with no problems. It's as loud as a Nascar fan with a megaphone, so I have to watch the volume level but it works fine. Any more than 25 on my volume (max is 37) and the distortion begins.I questioned that at first, but one of the sales reps at Crutchfield assured me it would be fine. He said the M&T head unit is nothing more than a factory radio. The amp is built to run off the speaker wires. It's just my HU puts out more power than the factory CD player does.

[DHelm72]

AJ,One thing the Crutchfield advisor didn't mention. You could buy a line level attenuator. With an attenuator you could adjust the input level of your head unit going to the factory amp. You could then adjust the input level so that there is no distortion at full volume. This way your input voltage would be properly matched to the factory amp and you wont risk clipping the amp and blowing your speakers.This is a possible idea. I bought a good attenuator on ebay from HLabs for about $20 a while ago for a friend's setup.

[AJ_'04 Vibe]

Thanks for your suggestion, but I'm perfectly happy with it now. I'm old and gray and don't listen to loud music very much anymore anyway.