I know this is a general stereo question, but I've posted on some Jeep boards, and not gotten any informative responses.

I have a 96 Jeep Grand Cherokee, with the factory "infinity" system. This system according to the wiring list I have, and according to some Jeep guys works like this:

Head unit is basically the same as in the non infinity systems, i.e. "high level". The speaker outs on this (labled as such on the head unit) go to the Infinity amp under the rear seat. The Infinity amp drives the speakers at a blistering 18Wpc.

Just for an experiment, I took my old 100Wpc amp (which I know works fine) and wired it in - using wire taps to the input connector of the infinity amp (I disconnected the infinity amp completely). I ran the wires to the "high level" inputs on my amp. Hooked it up to a sub I have lying around to see if it would work.

It did work, but I was able to get very very little volume out of the amp - like maybe 1/10th at most what it would normally be.

Question is this - How high level is high level? Is there a way I can test to see if they are really lo level? Would measuring the voltages help? With or without the amp (infinity or mine) connected?

Any thoughts on this are appreciated. Yes, I know, stock systems "suck" - but actually this one is not all that bad, and if I can "intercept" the signals before they go to the factory amp, and run them through my active x-over, and to my sub amp, it will sound even better....

Thanks, I know not totally empeg related - but I DO have an empeg in the loop here, and how this all works determines how I might wire up the next phase of my install...

-Jeff

The idea of "high level" of your aftermarket amp, and "high level" of the inputs on the Infinity amp are (as you discovered) two different things.

The infinity amp in your Jeep accepts inputs that are somewhere in between line level and speaker level. They are essentially line level that's been boosted a bit. The factory head unit's outputs are boosted to the exact amount that the Infinity amp expects. This is a totally different level than aftermarket stereos are designed to output. They do this on purpose, just to screw us up when we try to install aftermarket components.

The aftermarket amplifier is meant to take full-blown speaker inputs, with your already-fully-amplified head unit trying to supply enough power to move real speaker cones. Either that, or it's meant to take line-level input that's not amplified at all. But it doesn't have inputs designed to take the in-between outputs from your factory Infinity head unit.

The solutions to work around this are:

a) Dump the Infinity amp and the factory stereo altogether. Use the aftermarket amp the way it was intended: With an aftermarket head unit. Either with a fully powered head unit going into the speaker inputs, or with a line-level output from the head unit going to the amp's line-level inputs.

b) Connect your empeg (or any aftermarket stereo for that matter) to the infinity amp using an in-between factory-amp interface such as the PAC OEM-1. This is covered in the Installation Notes section of the empeg FAQ.

I've never heard of someone who wanted to keep the factory stereo and just upgrade the Infinity amp, so I don't know how you would do that (if that's what you're asking to do).

Try playing a constant sinenote (like found on test CDs) of 50/60 Hz at fairly loud volume, and take a AC volt meter to the wires.

As an example, to produce 22W (about what many modern HUs do (RMS, not the inflated peak numbers given in marketing)) into 4 Ohm, you need a RMS voltage of:

U=sqrt(PxR) (because P=U^2/R ) in this case we have P=22W and R=4Ohm, so U=9.38V (RMS)



/Michael

Thanks guys,

What I am (or was) trying to do is exactly that - kinda. I have options, but was just suprised at the outcome of my little test.

I wouldn't mind replacing the infinity amp if I have to, so the correct thing might be to run the factory head unit into a line-level converter, then into my active x-over, then into two new amps (one for speakers, one for sub).

What started all this, was the thought that I might just be able to run the sub amp by "piggybacking" and stealing signal from the factory system - essentially leaving the factory system alone. (Why, you ask? It sounds pretty good actually, and I like having the steering wheel controls. I know PAC makes the adaptor to make them do IR too, but I have only 5 buttons, and cant figure how Id make that to the empeg in any useful way)

So, If I turn up the volume to say 50-70%, and play a nice sine wave, and measure the output of the stock head unit, I should get some voltage, correct? (I'd be measuring AC?)

"line level" is what, 1-4volts or so? Should I make this measurement with the head unit connected to the inf system or my aftermarket amp?

(I trust that they are "in between" but I'd like to measure it anyway, just to see)

Thanks-
Jeff

Pre-out voltages on car HUs vary from 1V (rare these days) to (at least) 8V.

Exactly what you could use depends on what range you gain knob on the amp provides. If it can accept a 8V signal you might be good to go...

/Michael