Balanced design

Balanced audio has layers. The connector, the input receiver, the internal topology, and the speaker/output stage are separate facts. The table should not treat them as one checkbox.

Claim	What to look for	Meaning	Gotcha
Single-ended	RCA input/output, one signal conductor plus ground reference.	The normal unbalanced consumer-audio interface.	Short cable runs can be excellent. Single-ended is not automatically inferior.
Balanced connector	XLR or TRS connector carrying hot, cold, and shield/ground.	The interface may reject cable noise if the receiving input is truly balanced.	An XLR jack alone says nothing about the rest of the circuit.
Balanced input stage	Differential receiver or transformer input.	Rejects common-mode noise, then may convert to a single-ended internal signal.	This is the common spec-sheet gotcha: balanced input does not mean fully balanced amplifier.
Fully balanced / differential topology	Positive and negative signal phases are carried through mirrored gain stages.	The product is balanced internally, not just at the connector.	Needs an explicit maker claim or schematic/service evidence. Do not infer it from XLR input.
Bridged / BTL output	Load is driven between two active amplifier outputs.	Can increase voltage swing/power from two amplifier halves.	BTL can look balanced at the speaker terminals, but it is not the same claim as a fully balanced signal path.
Transformer balanced	Input or output transformer converts between balanced and single-ended domains.	Can provide isolation and common-mode rejection.	Transformer-coupled balanced I/O can be excellent, but it is a different topology from active fully differential circuitry.

How to tag products

▸`xlr_in`: the product has XLR inputs.
▸`balanced_in`: the input is electrically balanced, or the maker states balanced input behavior.
▸`balanced_out`: the product has balanced outputs.
▸`fully_balanced_topology`: the maker or service evidence says the internal signal path is fully balanced/differential.
▸`balanced_topology_notes`: use this for caveats such as "XLR input converted to single-ended" or "single-ended input transformer-coupled into balanced circuit".

Example to verify before tagging: some Bryston monoblocks are described by owners and documentation as fully balanced, while some stereo models have balanced inputs without a fully balanced internal signal path. The product row should cite the source that makes that distinction.