Output Coupling
Output coupling describes the electrical arrangement connecting a headphone amplifier's final stage to the headphones.
The output may use a transformer, a coupling capacitor or a direct connection without either. Transformers can transform voltage and impedance; capacitors block DC. Direct-coupled designs require appropriate control of unwanted DC. The category alone does not establish performance.
Output Coupling — Headphone Amp
The relevant coupling is at the stage actually driving the headphones, including the final stage of a hybrid amplifier. It can affect load matching and low-frequency behaviour, but measured results depend on implementation. Electrostatic equipment may use a transformer to obtain the high signal voltage its headphones need.
Compare output coupling alongside supported loads, output impedance and frequency response. 'Output transformerless', or OTL, only establishes the absence of an output transformer; it does not tell you whether a capacitor remains. Input capacitors, coupling between earlier stages or a DC servo alone do not identify the headphone output arrangement.