Inside the unit are four Accutronics® type 9 reverbs.
Physically, they are bolted together in clamshell pairs and surrounded on all six sides (and held in place snugly) by a resilient foam rubber lining. The padding is double-thick in front to provide extra protection when the unit is kicked.
Electrically, they are surrounded by impedance-matching circuitry using high-quality mil-spec audio transformers. The internal wiring is balanced and the reverb pairs are connected in a hum-bucking arrangement to minimize external hum pickup. Chassis ground is connected to pin 1 of the input connector. For each output, pin 1 is connected only to the internal shielding of the output circuitry.
Logically, this arrangement is like a reverb chamber; the outputs can be thought of as coming from a pair of microphones inside the box.
There is no possibility of ground loops.