Here's what I did this weekend:
1) Replaced the scavenged old Elna DC blocking caps with nice new Nichcon 4.7uF units.
2) Swapped the order that the subwoofer filters apply. Now I have the lowest Q filter applying first, as is proper when cascading multiple filters evidently.
3) Shortened the internal power and signal leads.
And the results:
1) The subwoofer turn off pop has returned. Not as loud as it once was, but loud enough to irritate.
2) There is some intermittent rumble occurring from the sub during steady state with no signal being sent to it. It sounds very similar to when I had the bad Elna DC blocking cap.
3) The subwoofer filter appears to do absolutely nothing at this point, although on the bench it test out perfectly. That makes it very difficult to fix.
3) To filter the engine noise I purchased a 4700uF "mini" cap which is about the size of a dachshund's dong and will never fit in the box. Then in an amazing feat of stupidity I added a 2000nF poly cap across the input power and wondered why it didn't help. I may just have to install the whole noise filter externally.
4) The phase curves for both the right and left channels are different from anything I have seen before. I can only guess that the Nichicon caps have enough phase shift that it's effecting the overall curve.
Next steps:
1) The Nichicon DC blocking caps are possessed by demons and must be removed. That's fairly obvious.
2) Check for bridges on the subwoofer board. Maybe get a new board and start over as these have seen a lot of rework.
3) Consider scrapping the second all-pass stage entirely in order to make room for the noise filter.
1) Replaced the scavenged old Elna DC blocking caps with nice new Nichcon 4.7uF units.
2) Swapped the order that the subwoofer filters apply. Now I have the lowest Q filter applying first, as is proper when cascading multiple filters evidently.
3) Shortened the internal power and signal leads.
And the results:
1) The subwoofer turn off pop has returned. Not as loud as it once was, but loud enough to irritate.
2) There is some intermittent rumble occurring from the sub during steady state with no signal being sent to it. It sounds very similar to when I had the bad Elna DC blocking cap.
3) The subwoofer filter appears to do absolutely nothing at this point, although on the bench it test out perfectly. That makes it very difficult to fix.
3) To filter the engine noise I purchased a 4700uF "mini" cap which is about the size of a dachshund's dong and will never fit in the box. Then in an amazing feat of stupidity I added a 2000nF poly cap across the input power and wondered why it didn't help. I may just have to install the whole noise filter externally.
4) The phase curves for both the right and left channels are different from anything I have seen before. I can only guess that the Nichicon caps have enough phase shift that it's effecting the overall curve.
An externally hosted image should be here but it was not working when we last tested it.
Next steps:
1) The Nichicon DC blocking caps are possessed by demons and must be removed. That's fairly obvious.
2) Check for bridges on the subwoofer board. Maybe get a new board and start over as these have seen a lot of rework.
3) Consider scrapping the second all-pass stage entirely in order to make room for the noise filter.