Well, I think I might try soldering a jumper wire in the H/K unit between audio ground and power ground. With the cold weather, this is actually the easier option. I opened the case and it is pretty straightforward inside there (with plenty of room).

I will report back once I try this...

Thanks!

 

After a little testing, I decided not to bother with the jumper wire.

I checked for continuity between the audio ground and the power ground.

It already appears to be connected (about .1 Ohms of resistance). I figured adding a jumper wouldn't do anything...

 

spiff72 — Your guess is probably as good as mine. In the Wiring Diagram there's a 2-conductor shielded lead. Its shield is labelled ASGN, and its internal conductors (the L and R channel signals) are labelled respectively ALI/ARI at the radio end, and ALO/ARO at the stereo jack adapter end. The shield is connected at both ends. There's also a lead labelled AUXI (non-NAV) or ADPG (NAV) at the radio end and AUXO at the adapter end. I think its purpose is to tell the radio that the adapter lead is properly connected, since there's a trouble code registered if it isn't connected (the lead to the adapter, that is, not any device you may connect to the adapter!). The 12-V power outlet of course also has a ground return lead, and it's the presence of these two paths that causes the ground loop.

By the way, even though you find only minimal resistance between the two grounds inside the H/K, it's still worth connecting them together right at the entrance to the device. This is to keep the interference from entering the H/K's case. I still think it's worth it to try lifting the one end of the audio cable's shield.

Ground loops are endemic. There must for safety reasons be separate ground returns for each connection, but this essentially guarantees that an interference problem is then possible. These ground-loop-type problems can occur in all consumer audio devices, for example, for this very reason. And they can be very difficult to cure after the fact.

Stan

 

Thanks, Stan...

I will try the jumper wire to connect the grounds when I get a chance. I might wait to try the shielding removal until the weather gets a bit warmer!

Now that you mention the extra wire in the aux connector, I am reminded that when I disconnect the plug from the aux port, the radio will automatically switch to another mode (since it knows that the source has been removed). I noticed that this only happens if you unplug the aux cable inside the console box - not when you unplug a device that may be plugged into the aux cable (like and ipod). Could this wire be introducing the noise? I would disconnect it, but as you said, this would send a trouble code. I am surprised that this is significant enough of an event to generate a code...

Would the likely method of this sensing wire be that it is connected to a normally closed switch in the outlet assembly, which is opened by inserting the minijack plug?

Thanks again,
Jeff

 

spiff72 — You're probably right. I don't think this sensing wire is likely to be the source of the interference problem. The easiest way to (temporarily) lift one end of the shield could be to make up a short stereo-to-stereo, male-to-female "adapter" cable with its shield open at the H/K end, and see if this changes the interference.

Stan

 

I will try anything at this point...

Just so I understand, I would not have to do anything with the car's wiring - I would just make up a stereo extension cable, and I would be breaking the connection at the shield at some point on the cable? I have never taken apart one of these minijack connectors...does the ground ring connect to this shield? Or does the ground ring connect to a separate conductor (meaning that there are actually four elements in the cable - left, right, ground, and shield)?

I would then take this cable, plug the male end into the aux port of the Camry, plug another cable (male-male) into the female of the "special" cable, and the other end of the male-male cable into the H/K? Could I accomplish the same thing by hacking up a male-male cable (like the cable I use right now), and connect this directly between the car aux port and the aux output of the H/K?

Thanks again for all your help! I have a coworker here who recognized your name. I appreciate the time you put into answering my questions.

 

spiff72 — That's all correct! If you buy a stereo jack/plug (or plug/plug) set (at say Radio Shack) you'll see that there are only 3 connections. The shield goes to the outside metal housing of the jack, and the "body" of the plug. The L channel "live" goes to the "tip" and the R channel "live" goes to the small "ring" of the plug. You'll easily see which of the contacts these correspond to on the jack. Just leave the shield unconnected at the H/K end. Or, as you say, you could just "hack" an existing extension cable for the experiment.

Stan

 

I have to resurrect this thread!

JeffD, can you answer a question about the op-amp voltage follower solution? If I did this, would my circuit actually require (2) op-amps - one for the left channel, and one for the right? I would also be interested to know if there was a simple way to implement an "auto-off" function that would shut off the device to save battery life on the 9 volt batteries when the car is shut off (maybe this could be implemented based on the lack of signal on the output of the HK)?

Thanks again

 

One more question - I am looking up examples for the voltage follower circuits, and I am wondering where the capacitors would be used (would they be in series with the output of the opamps)? Or would they be on the input side?

Thanks again!

 

I have just posted Canadian TSB2810 (= US TSB_AU004-07) covering the solution to this problem, titled "Noise from Auxiliary Port with External Device," in the thread "List of pertinent TSB's." There's a revised AUX socket assembly, connector cable, and in-line filter module that get fitted in place of the original AUX socket to resolve the noise problem caused by ground loops that occurs when the auxiliary device is playing while being powered by the car's 12-V system.

Stan