Harman AKG C4000 Modo De Empleo página 14

Powering
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In order to preserve symmetry, use 2 x Rv resistors with a maximum tolerance
of 0.5% only.
If the amplifier inputs are single-ended (grounded) or have no input
transformers, wire either capacitors or optional transformers into the audio
lines to prevent any current leakage into the input stage.
Adding Phantom Power to Unbalanced Amplifier Inputs
C4000