KSPIV head doesn't talk with factory amp / DSP about expedition HOT 5 OPEN

After investigating #6, I think this may be a problem with the DSP in my truck and not the KSPIV head. I'm going to have to break out the oscope and start checking some clean signals at various points in the path.

from expedition.

Looking at the speaker output from the head, it looks completely clean up until 37 on the volume dial. At 37, it gets some clipping that gets worse as you top out the volume. Being that the distortion I hear in the truck starts at much lower volumes, I don't think the head is at fault.

40Hz Sine, Volume 37

40Hz Sine, Volume 40

2kHz Triangle, Volume 37

2kHz Triangle, Volume 40

440Hz Triangle, Volume 37

440Hz Sine, Volume 37

from expedition.

Looking at the front passenger woofer connection, we can see that the signal is already pretty much garbage at Volume 30, gets much worse as you go higher, and is a complete mess, not just clipped. The lower Vpp at the higher frequencies for the same volumes is due to the low-pass filter in the DSP between the KSPIV head and the speakers. Given the relatively clean signal coming out of the head and the hot mess at the speakers, I'm thinking the DSP is probably bad.

40Hz Sine, Volume 30

40Hz Sine, Volume 40

2kHz Sine, Volume 30

2kHz Sine, Volume 40

200Hz Sine, Volume 30

from expedition.

Grabbed a new-to-me DSP on eBay for <$100 -- looks like Ford used FB5T18B849AH / FB5T18B849AG in a bunch of different models. Not sure what the difference is between the H and G models, but the one I picked up came out of the same year and model as my truck. Now I just have to wait for it to get here.

from expedition.

Confirmed today this is not an amplifier problem, but rather a CAN bus communication problem. I connected the OEM head, set the volume to Max-5, then reconnected the KSPIV head. I now have quality sounds up to higher-than-comfortable listening levels.

Keeping this open still as the head really needs to talk to the amplifier on I-CAN to manage volume settings properly as opposed to keeping the amp driving hard all the time and attenuating at the head. I'll need to confirm with a scope, but I bet the OEM head doesn't change its output levels at all for volume / balance / fade and just outsources all of that to the amp over I-CAN.

from expedition.