This is probably going to be very long winded and keep in mind that I'm inexperienced when it comes to car audio.
I installed a Toyota navigation system from a 2004 Toyota Solara into a 2004 Toyota Sienna. The system is just about plug and play with the exception of the voice navigation signal. The Nav unit put out what appears to be a preamp'd voice signal. I was able to take this 2 wire out signal and input it into a radioshack 7.5watt amplifier and drive it into a small 3 inch speaker. Problem was that the RS amp is just not enough. At max volume out on the Nav system the voice is hard to hear at highway speeds. I then tried to install an older JBL (18w @ 4ohm) amp and here is where I'm having problems.
When I input the voice out into a single channel of the amp through the low level input the sound was more than loud enough at the mid range of the volume control of the Nav unit. I had the line level adjust on the amp at minimum and it worked until I turned the ignition to ON or started the engine. As soon as the key was rotated to ON the speaker would emit a buzzing/noise that did not increase or decrease with the NAV volume control but was pretty constant. If I returned the key to the ACC position the speaker buzzing/noise would go away.
I then connected the voice out signal to the High level input on the JBL amp and tried again. When set up this way the sound was clear and the buzzing/noise was not there in ON or when the car was running. Problem was the sound is not loud enough even a the highest setting of the Navigation volume control in this configuration.
I realize that the low level signal probably amplifies that signal greater then the high level signal and in turn probably amplifies the noise also. But when I used the high level input there was no noise, not less noise but no noise.
Some details that might assist helping me:
I was using the cig lighter/accesor plug for powering the amp as a temporary solution so the ground for the Nav and the cig lighter/accesor plug were not shared. I could try making sure the ground is shared and try it again but I'm not holding out any hope.
Any assistance would be appreciated.
Thanx,
jeff
You could temporarily run a ground from the battery with your low level setup and see if that cures the noise. Im surprised the high level inputs didnt make noise assuming you changed nothing else.