Awhile back I wrote about how I added the ability to plug my iPod into the factory CD changer in my Honda Accord. Unfortunately, that wasn't the end of the story. I kept running into noise problems -- I was hearing alternator whine through the sound system, which increased in volume and frequency at highway speeds, and a low-level buzzing from my cellphone charger that became intolerable when I had to increase the volume when traveling on the highway. Putting noise suppressors between the iPod and the car system did not help at all.
Fortunately, I have two things in my favor: audio has been a lifelong hobby, and I have a BSEE degree. :-) I knew that these issues were at least partially caused by ground loops. I had tried earlier to get the mobile electronics guys who were doing the installations for me to fix them, but sadly enough they didn't seem to get it. So, I learned how to take my own center console apart to reach the factory CD changer's auxiliary input. After that, it was easy. My connections go like this:
- A Soundgate SNHOND3 adapter plugs into the factory CD changer auxiliary adapter. It has no power connections, and it provides RCA jacks for input.
- A Precision Interface Electronics (PIE) EIS-ILNO noise eliminator plugs into the Soundgate adapter. This provides protection against radiated noise, such as what I was picking up from my cellphone charger. This is a passive component (i.e., no power hookup).
- A PIE LD-1 adjustable line driver plugs into the noise eliminator. This boosts the line level of my iPod (which is an old mechanical wheel model) so that it roughly matches that of the CD player and radio. It requires a 12VDC hookup.
- A Radio Shack ground loop isolator plugs into the line driver. Despite the fact that the line driver is tied into the same power and ground lines that I use to power the iPod, I was still getting noise, and this isolator eliminates it.
- A Metra NF-12 noise filter for the power hookup. This eliminates the alternator whine. I used a 12 amp filter rather than the NF-5, rated at 5 amps, because the power port in the Accord center console is rated at 10 amps. I hooked this into the power line that leads to the center console power port, then powered the LD-1 line driver off the same line.
- I use a Sik Imp to power my iPod. It's not the most sturdy thing in the world, since twisting it (as you often need to do to push it into the power port) can make it lose its connection, but plug it into the center console power port and leave it there, and you're fine. Note that since I plug this into the center console, the NF-12 cleans the power for it too.
- A simple RCA to 1/8" adapter cable runs from the iPods into the ground loop isolator. I just ran the cables out of the bottom of the center console near the front passenger seat. From there, I can easily plug it into the iPod, and then rest my iPod in one of the center drink holders.
With all this in place, there is no audible noise whatsoever. Most excellent.