UHF (U4/U4D) series wireless receiver: what is the structure of the output circuitry? Is it a chain of inverters, emulating a grounded-center-tap transformer winding? Or is it a cross-coupled output stage, emulating a floating transformer winding? What happens in the presence of 48V phantom power?
From the U4 receiver service manual: "The output stage consists of an inverting amplifier stage, the output of which goes directly to one pin (pin 2) of an XLR connector. A 180 degree phase-shifted version of the same signal is obtained by tapping off of this point and entering another inverting stage. This phase-shifted version then goes to another pin (pin 3) on the XLR connector."
The U4 XLR output is protected from 48 volt phantom by having a 47µF/63V capacitor in series with each XLR leg.
The complete U series service manual is available at nominal cost from Shure Service. Call 800-516-2525.