Good comments by Erik and Kijanki, as usual.
A clarification to comments a couple of people have made, to the effect that a fully balanced amp requires essentially two separate amps on one chassis, one amp for each polarity of the balanced signal pair. The implication being that twice as many parts are necessary than would be required for a comparable single-ended signal path.
That is one approach to implementation of a fully balanced amp. But another approach, which I suspect is used more frequently, is to use a differential stage, having differential inputs and differential outputs, for each of the active stages in the signal path.
See the section on "differential amplifiers" in this paper at Ralph’s Atma-Sphere site for a simplified schematic representation of a tube-based differential stage, and also for a summary of the advantages and disadvantages of that approach. Note this statement in the disadvantages section:
-- Al
A clarification to comments a couple of people have made, to the effect that a fully balanced amp requires essentially two separate amps on one chassis, one amp for each polarity of the balanced signal pair. The implication being that twice as many parts are necessary than would be required for a comparable single-ended signal path.
That is one approach to implementation of a fully balanced amp. But another approach, which I suspect is used more frequently, is to use a differential stage, having differential inputs and differential outputs, for each of the active stages in the signal path.
See the section on "differential amplifiers" in this paper at Ralph’s Atma-Sphere site for a simplified schematic representation of a tube-based differential stage, and also for a summary of the advantages and disadvantages of that approach. Note this statement in the disadvantages section:
Differential amplification takes more parts to execute. For a given number of stages of gain, differential amplifiers have about 50% more parts.Regards,
-- Al