Just a quick yes no question. Can I wire an amp to a factory deck as shown, with out causing any damage to the head unit's amplifier?

 

I say no, I """think""" youll be not letting enoght power to the rear speakers........you could always get speaker in line inverters switching the signal to rca jack low output leaving all the decks amp sound going to the rear speackers.

 

wouldn't running a tap off the rears into the high level input be the same as running line converters??

 

yes, you could could do that either at the speakers or at the radio.

 

Well i assumed the amp would be robbing half of the amplified sound comeing from the sterio but i dont know for sure....... like i said "i think"!!

 

Yes you can. Most quality amps use 1:1 isolation in the inputs at the RCA and speaker inputs. This gives them a higher input impedance so the load to you deck will be almost the same. Note that I said Quality amps. If you go with a cheap amp they will more then likely NOT have a vary high input impedance and may give you some problems. Still shouldn’t do anything to your deck, just may give you some noise and less then flat response, but that’s a problem with cheaper amps any way.

 

The amp I was looking at is the Pioneer 250 watt 2 channel..

 

What model #? You may not what that.

 

I hope its not a x372. or x972 I like the quality amp reply

 

Well it I was thinking of the X372... is that a bad choice?? any other ideas.. affordable ones..

 

The GM-X372, GM-X374 are the only two in that line that are not under recall right now. Not bad amps just use the right power and ground wire, make a good ground first! NEVER have the ground disconnected with the RCAs plugged in.

If your buying it used check the bottom of the amp. There should be a green magic marker dot next to the serial number, if there’s no green dot DON’T buy the amp.

There is a mod that ALL the amps in the line need, the ones with the green dot got it form the factory.
No green dot, no factory mod, FETs (in the amp) on fire = NOT GOOD.
Green dot your all good.
Pioneer is doing some new things in that amp and the first time a company puts out a new technology sometimes it takes some time to get it right. It’s not to say Pioneer is junk, there NOT. They just didn’t catch a small design goof that’s not a problem in a test lab but is a problem in a car.

 

Ah, ok.. thansk for the info.

 

What's the input impedance on your amp?

Your head unit is designed to take a 4 Ohm speaker; if your amp has a a similar input impedance and you wire them in parrallel (as in your diagram) you will effectivly be running a 2 ohm speaker off your head unit; this will double the amount of current going through the amp in the head unit and thus it'll get very hot and could kill it.

If you amp has a high impedance input you'll probably be OK from a damage point of view but the signal going to the amp will be very deminished.

You could try wiring them in series (1 wire from the speaker and 1 wire from the amp goes to the head unit the other 2 wires are joined together). This will add the impedances together (so you will be effectivly running an 8ohm speaker) this will reduce the output of your head unit slightly but will stop any damage and should prevent the imput to your amp being deminished.


Matthew

 

GM-X372: Input impedance at RCA in=22Kohm
Input impedance at speaker level in=40Kohm

The lowest speaker level input impedance I’ve seen on an amp was just under 100ohms and that was on a CHEAP Roadgear crap amp. No where near 4ohms.

 

Car speakers are rated at 4Ohms, Hi-Fi ones are usually 8.

It usually says on the heat sink on the back of the speaker cone its impedance.

 

Thanks for the news flash. :lala:

 

Sarcasm!

So if you wire a 22KR and a 4R load in parrallel there will be 5500 times as much current going through the 4R load than the 22KR one. Thus you'll hardly get any signal to your external amp.

Which is what I was trying to explain.

So it won't blow your head unit but will sound very quiet.

Matthew

 

take that HI-level input plug and throw it in the trash.

yes...throw it in the trash.

SQ from those is a joke, spend the extra cash on a LOC and run some RCA's to the amp. you can save some cash by using really short RCA's if you run the LOC from the speaker wires (you can extend the speaker wires too) nearest to the amp.

Now if you are really cheap, you can hook up an RCA plug directly to the speaker wiring and turn the gain all the way down and just let it up very little to get the signal. Just remember....keep that gain DOWN!

 

Sarcasm, me, never.

You are absolutely right on this part.

Not here.
The isolation amp, (the first stage) is “looking” only at the voltage at the speaker level input, NOT the current. That why there is such a high input impedance (40K ohm, 22K was the RCA input) at the speaker level input. The speaker level input is designed to be used this way or with out the 4ohm speaker load. Voltage will be the same in his parallel circuit.

 

I've pretty much decided to get two good quality High to Low Level converters. then do the RCA's to the amp.. and run a 4 channel amp to drive the main speakers, and a second amp to drive a 12 inch sub.

 

Much better choice.

 

qube, as a peace offering let me try to explain it this way.

Lets run the numbers. Use 10V DC to make thing E-Z. In this circuit with DC Current at point B or though branch B you will have 2.5Adc. At point C or through branch C you will have 0.00025Adc (0.25mAdc). This will give you a total current at point A of 2.50025Adc. Now if you eliminate R2 (40Kohm) R1 will still have 10Vdc so the current at point B will still be 2.5A. By adding R2 back the circuit you don’t change the current at point B, just the total circuit current at point A. Same thing happens if you eliminate R1 (4ohm). You still have 10V across R2 so you still have 0.00025 (0.25mA) at point C.
Now there is one fly in the butter when you move this theoretical into the land of the real world. Most of the amps in a HU will put out a little more voltage under a no-load (or vary low load) condition. So if you had the amp hooked up and where sitting there unhooking the speaker the signal out of the amp may get a little louder, not because the HU is putting out more power, it’s not, but because the voltage out of the amp may be a LITTLE higher. But this would be a vary small change, not even note worthy.

 

wow, you guys are really NUKING this problem.

you all should be doing R&D for some electronics company.

 

I kinda do from time to time.

And it's not to beat a dead horse, just trying to explain.