Is it possible to bridge an OEM (Infinity) Grand Cherokee Amp? - diyAudio
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Old 18th October 2011, 06:56 PM   #1
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Question Is it possible to bridge an OEM (Infinity) Grand Cherokee Amp?

Hello everyone. I have a 1997 Jeep Grand Cherokee and it has a stock amp that I would like to continue to use, but I would prefer to make it a 2 channel amp instead of it's 4 channel OEM state. I don't know too much about it other than it's built by infinity and supposedly is 120 watts (30 x 4) into 2 ohm speakers. I'm kind of surprised about 2 ohms but that's what I've read and I don't have the stock speakers to check. Is there a way to do this?

Thanks,
Howard
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Old 19th October 2011, 06:42 PM   #2
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first thing you need to do is check how it interfaces with the head unit/system. likely, if it is possible, it would need to have a power supply to run higher voltages, a common per pair of speakers on the output with + and - rail voltages, and the ability to invert the signal on half of the corresponding inputs, just to start with.
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Old 19th October 2011, 07:02 PM   #3
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I'm going to try and attach a picture which shows a 1999 amp, which is almost exactly like my amp. I do know that my amp takes amplified radio power and sends it's amplified signal out from there (no RCA jacks). In the picture is a shot of the board without the heat sink case. Unfortunately I don't know how to check for the rest of your suggestions, is there something I can measure?
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Old 19th October 2011, 11:55 PM   #4
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There don't appear to be any power supply FETs on the board which means that the internal amplifiers are operating from 12v. If that's true, each channel is already bridged. Measure the DC voltage on each speaker output pin (black probe on a known good ground). If all read ~6v, the amp already uses a bridged pair for each speaker.
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Old 20th October 2011, 02:42 PM   #5
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I'm assuming the voltage is only present when the amp is on, being fed a signal, and trying to provide it to the speakers? Then I find a ground point for my voltmeter and probe both the positive and negative (individually) for each speaker?

Thanks for the help,
Howard
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Old 20th October 2011, 05:27 PM   #6
sdoom is offline sdoom  Germany
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from what I can see on the picture the amp uses 3 chip-amplifiers which would probably result in a 6-channel amplifier unit. They probably combine some front door and upper speakers. If you can find out what kind of chip they used it might be possible to put the chip into bridged mode. but I doubt that you can bridge the chip without opening and resoldering the amp. And of course, the power-ratings of those chip-amps is usually given while running @ 16V, furthermore the noise that those chip amps produce when bridged is usually much higher. IŽd rather try to somehow get the low-level (= RCA level) signal out off the head-unit and drive a seperate amplifier
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Old 20th October 2011, 05:56 PM   #7
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#5:
Probably and yes.
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Old 22nd October 2011, 01:18 AM   #8
ppia600 is offline ppia600  United States
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I don't believe it is bridgeable (without substantial re engineering of the board setup) due to the individual 12v ic's (like others have mentioned) used for each channel. Each channel is also already crossed over and that also limits your flexibility. Some of the decks used in that infinity/chrysler system ran a voltage similar to a normal deck to drive that amp, but the deck alone isn't designed to drive speaker loads so if you end up not using the amp you may want to change the deck also. If you really wanted to keep the amp you could run dual voice coil subs to keep the channels isolated and then use an aftermarket deck to drive some (aftermarket 4 ohm) door speakers.

I used to have a pile of these amps from the concordes and cherokees from customers not wanting them after changing to aftermarket but I ended up scrapping them to a guy for aluminum.
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Last edited by ppia600; 22nd October 2011 at 01:21 AM.
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Old 22nd October 2011, 05:42 PM   #9
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actually, i do know that there are chip ic's that are bridgeable to 4ohms, if each channel is 2ohm stable, and one of the signals is inverted. my deh-p800r has that very feature built into the rear channels, however it is pointless without a power supply to raise the rail voltage. i see a torroid on the amp, which could possibly be the transformer, or not. if the chips are already bridged, then you are stuck with what you have. the 4 input channels, power/ground wires, and remote are already identified in the legend, and the databuss is likely just to do with the bcm check/fault. if they are like most average chips like that, then they will have 4 ouput channels per, with power control, though you would have to see how it's set-up. quite possibly, each one has bridged outputs already for the total 6 channels, and nothing left for power supply switching. just knowing about the factory door speakers, they do not handle much power at all, suggesting that it does not put out more than 11.x volts, hence no power supply. i cooked a pair this summer in a small test box on about 50-60watts rms pretty quick, so idk. if it would be possible, the way it would work is to swap +/- on one side of the input wires, either right, or left... but that would be if it is possible, and it's all you on taking the risk of frying the amp and/or head. an aftermarket amp and speakers is a better bet.
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Old 22nd October 2011, 07:02 PM   #10
ppia600 is offline ppia600  United States
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While its true that many ic's are bridgeable, I doubt by the questions asked by the OP that he plans on reengineering the circuit board to bridge an oem amp. Many of the cheap small aftermarket chip amps are just bridged ic's with crappy damping and high distortion and run on 12v. I do remember several pioneer decks being 2 ohm stable on a rear channel but only being able to run one when doing this and I don't remember the schematics specifying that you had to run one channel or the other. Seemed like running only one channel at 2 ohm was more to avoid a thermal issue rather than some type of bridge configuration. Do you have the wiring diagram for that pioneer? I've never seen one that you could bridge both rears into one, interesting stuff.


Quote:
Originally Posted by AKHeathen View Post
actually, i do know that there are chip ic's that are bridgeable to 4ohms, if each channel is 2ohm stable, and one of the signals is inverted. my deh-p800r has that very feature built into the rear channels, however it is pointless without a power supply to raise the rail voltage. i see a torroid on the amp, which could possibly be the transformer, or not. if the chips are already bridged, then you are stuck with what you have. the 4 input channels, power/ground wires, and remote are already identified in the legend, and the databuss is likely just to do with the bcm check/fault. if they are like most average chips like that, then they will have 4 ouput channels per, with power control, though you would have to see how it's set-up. quite possibly, each one has bridged outputs already for the total 6 channels, and nothing left for power supply switching. just knowing about the factory door speakers, they do not handle much power at all, suggesting that it does not put out more than 11.x volts, hence no power supply. i cooked a pair this summer in a small test box on about 50-60watts rms pretty quick, so idk. if it would be possible, the way it would work is to swap +/- on one side of the input wires, either right, or left... but that would be if it is possible, and it's all you on taking the risk of frying the amp and/or head. an aftermarket amp and speakers is a better bet.
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