New Nav install w problems
 

I recently had a Pioneer X850BT installed in my 2012 Z roadster. There is an annoying hiss coming from my stock Bose speakers even when the audio is off. The installer has no idea what's causing it. Any audiophiles out there with a solution would be greatly appreciated. Gene

HU, but no amp installed?

Hiss usually is caused from an improper ground or grounded signal wire feeding the speakers or the source in which is playing. It's not always the culprit, however in many instances it is. I would start checking grounds, and I would also if you have the scosche harness like i do, utilize the extra Black Terminal'd ground that is in it and ground to your chassis inside the area where you mount the deck. Start there and work your way to the speakers.

More info would be helpful. I highly doubt that its a ground issue, however. Are you saying that it is hissing when the unit is powered off, or just when the audio from the Nav is muted?
It sounds to me like a Source Level Adjustment issue.

did the installer use speaker to line level converters? is that wats causing the hissing?

the 850BT has only 2v or 2.5v preouts, not enough for the bose inputs i dont think.

Ground problems are usually accompanied by "buzzing" or feedback, not hiss. Hiss is usually a sign of noisy electronics or gain set too high. I'd check for: Gain too high on amp / gain too low on pre-amp or a noisy amp and/or pre-amp.

Yep you nailed it on the head! Bose wants at least 4 volts being fed to it otherwise it can cause problems.

Can't change the gain on the bose head amp.

4 Volts is at maximum, or nominal, BAF? You know that at nominal to low listening level the head unit isn't putting 4V out right? 4 V is maximum level. I think you may be confusing impedance with voltage? Voltage varies with level and impedance varies with frequency. In the case of line outputs usually the output op amps are low impedance 600 to 1000 ohms, and the inputs of the power amp are usually high impedance up to 10K typically. Those values are typically chosen because the designer considers the long runs of cable needing a low impedance to drive them to reduce the losses and the resistance to the capacitance contained in the system cabling to affect high frequency response. Resistance value doesn't change with frequency so that's why they are used to terminate op amp inputs and outputs.

in this case a lot of noise high frequency sounds like mismatched gains. I would mute the head unit output and see if the hiss lessens-it's a "divide and conquer" scenario. If one really has to one could build a voltage divider to drop head unit nominal output by whatever amount you need to. Divide the level, drop the hiss, etc., to match what the BOSE amp wants to see. I can't help but think 1V RMS is enough to drive it to clipping...

:iagree:
All that being said, To the OP I say this.... Take the car back to your installer, and have him properly adjust the adapter he tapped in between your Aftermarket HU and your Bose amp. Should take him about 10 seconds to dial it in to remove the hiss. (there are adjustment screws on the front of it for left and right) OR you can locate it yourself (he probably installed it behind your HU, and do your own adjusting.

I know what your saying however from my experience with bose systems seem to hate any pre out voltage lower than 4 volt pre. Given that you can not change gains on a stock bose amp I think the OP needs to change head units.

I don't think he is going to be able to do this given I bet the harness they used is this.

http://www.autotoys.com/pics/70-7553.jpg

If so, thats where the problem lies. He needs to get a speaker out converter, and forget the line level outs.
I can definitely see where that would cause an issue.

the installer shouldve known that the bose needs 4v preamp and to run the avic-150bhs, or one of the 7" doubledins from pioneer + U250 nav module to begin with.

unless ofcourse, if he know wat he was doing with the speaker to line level converter.

Scosche makes an adapter using speaker level outs from head unit, simply splice it into speaker leads, and adjust away.