I have a stock Grand Cherokee 5.9 HU that came with a multi channel amp (Infinity) under the seat. Im replacing the amp and cant tell if the HU output in pre-amp or speaker level. How do I tell? I have voltmeters etc. Thanks
Just clarifing, your asking how to tell if your HU has Pre-amp (RCA) outputs or hi-lo speaker level converted. Most to no stock HU have pre-amp outputs, you can check by seeing if there is anything on the back that looks like you can plug RCAs into. Usually stock, amps that come with the vehical just have a bucnch of small wires, not anything like RCAs and thick power wire. So to replace that amp you will mostlikely have to re-run a power and ground, remote and RCAs, RCAs can be run two ways, using exsiting pre outs (if the HU has them) or buying a seperate Hi-lo converter, which converts the frequencies of 2 speakers (left and right both the + and -'s). This is done by just splicing the 4 wires on the stock wiring harness. Here is what you would need (of course by looking on the internet you can find them cheaper). http://www.tune-town.com/installation/line_out_reducers.asp
I'm not a big fan of thsoe hi/lo line converters. They add distortion and can lead to a significant loss of frequency response. If you can find some speaker preouts under say 4 volts I'd think you be better off soldering them up to some female rca plugs.
If you have a wiring diagram and can isolate the correct speaker preouts measure the a/c voltage across say right front pos/neg. If its under about 4 volts(or greater depending on your amp) at 3/4 volume then you should be good.
Maybe Jonathan can recommend a good line converter but my experience with the things hasn't been great, course I'm kinda picky.
Yep the Stock HU has the standard Chrysler wire harness on the back running to the amp, then to the speakers. My new Amp has pre-amp ins(RCAs) and Speaker level ins (molex plug). I just dont know which in to use on the amp. I suppose I could hook up a speak direct to the HU outs and if it makes enough noise I assume speaker level out? But how loud should it be?
lol, yeah that was my gauge, but there's a few amps that can handle crazy amounts of voltage. It sure would be easiest just to use the hi level inputs on your amp but I'm not positive your SQ won't suffer as a result. Again I'm not sure how the hi level inputs work on amplifiers. If they just use a stepdown transformer like like those line converters then I'd think you lose some sound quality.
If it were me I'd put in a "loud" cd and start measurin voltages and stuff, but I like messin with those kinda things.
Most high level inputs sound like crap compared to an RCA line. Sorry. The high levels of an amp are (usually) the same as a line out converter, just a step down transformer. Problem is, with an LOC you need to convert to low level as soon as possible for least noise, but it still limits freq. response and increases noise and distortion. If you must use the factory head unit, soundgate makes good LOCs.
Right but Im banking on not needing the LOCs, if the HU out voltage is low enough. My new amp is a JL Audio e6450. Has input sensitivity adjusters on the preins. Dont know how much VAC the amp preins can handle.
The head unit's amp will put out at least the same voltage as your charging system at full power, somewhere between 12-14.4V. If the amp uses a transformer (such as the Alpine V-drives) voltage will be even higher than that. That's why an LOC is needed, or use high level inputs (which I don't recommend)
Oh, by the way that 12-14.4V will be the peak voltage, RMS would be about .707 of peak (theoretically) so 8.5V minimum RMS signal coming from the head unit. When the car is running, it'd be over 10V RMS more than likely.