Although it may not help your problem, instead of connecting the sub’s negative input terminals to the amp’s negative output terminals, try connecting the sub’s negative input terminals to a chassis screw (or screws) on the amp. That is what REL recommends, for example, when connecting their subs at speaker-level to amps that have balanced or bridged outputs.
There is a slight possibility that doing so could result in significant hum, depending on the internal grounding configuration of the amp. But assuming hum doesn’t occur that approach would be preferable to grounding the full amplitude signals that are present on the amp’s negative output terminals through an unknown and possibly very low impedance in the sub. Which, depending on the internal grounding configuration of the sub and the amp, could conceivably result in damage to both components, eventually if not sooner.
Good luck. Regards,
-- Al
There is a slight possibility that doing so could result in significant hum, depending on the internal grounding configuration of the amp. But assuming hum doesn’t occur that approach would be preferable to grounding the full amplitude signals that are present on the amp’s negative output terminals through an unknown and possibly very low impedance in the sub. Which, depending on the internal grounding configuration of the sub and the amp, could conceivably result in damage to both components, eventually if not sooner.
Good luck. Regards,
-- Al