Several folks have inquired about whether certain Aragon or
Acurus amps are "common-ground" or not with respect to their
amplifier outputs. As with most things, the devil is in the details when it comes
to answering that question because there are usually some underlying
application issues that raise the query in the first place. Here's the general summary:
Most of the topologies that Aragon and Acurus amps employed from the very beginning are common ground in that the connected loudspeaker has a plus (usually red) terminal connected to the amplifier output and a minus terminal (usually black) which is tied somehow to an internal common grounding point (to be at about the same potential as the incoming signal ground and at the chassis ground and, hopefully (if the grounding terminal hasn't been tampered with), at the outlet ground. The notable Aragon exceptions are the balanced monoblocks (Palladiums), which follow more of a BTL or "Bridge-Tied-Load" approach in which one channel module drives the plus terminal and another drives the minus terminal.
Further, the speaker minus terminals in most of the Acurus models (including the Klipsch Aragon 2000 and 3000 series) remain connected to chassis ground even in power-off mode. However, the higher-power, non-Palladium Aragon amp models, including the 8008, 8008x3, etc, disconnect both the plus and minus speaker terminals with power off, thus "floating" the speaker ground terminal until power is on and the channel output relays connect. With the amp on and the output relays engaged, there is still a small resistance between the negative speaker terminals and chassis ground. This is a normal characteristic of its safety-related ground protection circuitry that should not be defeated by attempting to strap the minus leads together or by strapping the minus leads to the chassis.
The high-powered Aragon architecture, while having significant benefits for safety and performance, has been known result in hum when paired with a certain few loudspeakers that rely on an amplifier minus lead that is constantly connected to ground and/or has a common ground (direct) connection between amp channel minus terminals. As with any complex audio system, insofar as possible, keeping connected components grounded in a common outlet and as close in proximity as physically possible will minimize hum issues. Modifying amplifier ground connections or other similar measures that unintentionally defeat the designed-in safety mechanisms is never recommended.
Hopefully the above provides some application insights based on how these amps are designed.