1176 mnats rev J - Low end rolloff

[jonsibar]

Hi!

I built an 1176 mnats rev J a few years ago, and I'm having an issue with a dramatic rolloff in the low end.
Tracing the audio-signal for testing, it sounds perfectly okay and compressed on the primary side of the LL5402 output tranny, but weak and thin on the secondary. I replaced the LL5402 just to check if it had a problem, but that didn't help.

I've been searching a bit on this forum and elsewhere without finding a possible solution. Could it be impedance-related? I would really appreciate a few hints on where to troubleshoot further!

 

[jonsibar]

Did some more troubleshooting, and seems like it may be an issue with hot/cold/ground. Not that I can figure out why this happens just yet...

 

[jonsibar]

Tried with unbalanced cables now, and hey presto! Seems to be some kind of phase cancellation at play... does anyone have any tips?