Best Of

Left and right was the first thing I checked when the crate arrived and when I opened the box. Confirmed.

At least with the old SDA design for which there are a few schematics in the wild, AMP OUT 1 was basically pushing SPEAKER 1 and SDA 2, which was all then tied back with a common ground internally to AMP OUT 2. Vice versa for AMP OUT 2. I need to test again with SDA connected and one of the amp channels off. It *should* cause one speaker to play, and one SDA to play, with the crackling on the SDA channel. If it doesn't, the crossover is more complex. Heading home to try more configurations and pieces of gear to (hopefully) figure out what's gone wrong.

The Parasound HCA-3500 is an old amp. If it has not been serviced, it is well past it's prime, no matter what the weight is. Electronics age and wear out plain and simple. If it were mine I find an authorized service center and have them go through it and replace ALL resistors, capacitors and miscellaneous parts that have worn out and all service bulletins issued on the amp. That should get you another 20+ years

Maybe start with contacting Parasound, they've in the past have been very helpful with helping finding or having you ship directly to them. Excellent customer service.