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The manual says that when you connect the XLR to a TS plug, you should connect XLR pin 3 to the sleeve of the TS jack. Therefore, this must be a "ground compensated" (what you're calling "quasi-floating") output circuit.


Okay, the circuit Self refers to as "ground-cancelling" (fig. 5a) is kind of an oddball that in my experience is not at all common. It is an unbalanced output with, like it says, compensation for ground noise. That's not what I was talking about.

The "Balance line output" (fig 5b) is the typical non-compensated, electronically balanced output. This is similar to the circuit I used in my Super Stereo compressor. Its advantages are its simplicity and its short signal path. The disadvantage is that special consideration is needed when feeding an unbalanced load. Most other arrangements allow you to simply tie Pin 3 to ground, and away you go. In this circuit, which is fairly common, grounding Pin 3 makes the inverted output somewhat unhappy (though most decent op amps can handle it okay) and it can also dump a lot of highly-distorted signal current into the ground. If either the source or the load are laid out poorly in terms of their ground scheme, this can be an ugly scene. Also, you get 6dB less signal when feeding an unbalanced load. For the purposes of the Super Stereo compressor, I felt these were acceptable limitations since it's being marketed to high-end post-production applications where it will be interfacing with balanced loads and/or well-planned and well-executed interconnection schemes.

The Quasi-Floating Output (fig 6) is the one I was discussing in my previous post. This is basically a version of the balanced circuit that's been modified to eliminate the two compromises I mentioned above. The only real drawbacks to this circuit are that it's more complicated than the regular electronically-balanced circuit, with higher parts count and longer signal path. Of course it still doesn't offer the galvanic isolation of an actual transformer.

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