Amplifier Output Measurement Chains

Definition: every probe, attenuator, current sensor, analyzer input, filter, scope channel, calibration, range, timing relationship, and safety rating between the amplifier terminals and the reported result.

Start With Output Topology

Treat both output terminals as active until the amplifier is proven single-ended. Bridge, BTL, floating, and many class-D outputs must be measured with a suitable differential or isolated method. Do not connect an ordinary earth-referenced scope ground to an unknown output terminal.

Voltage Path

Verify differential and common-mode voltage range.
Record probe attenuation, input impedance, capacitance and bandwidth.
Zero and compensate the probe before the run.
Use stable guarded test points rather than hand-held repositioning under power.
Check that the probe, attenuator, cable and analyzer remain unclipped.

Current Path

Use a current probe, clamp, current transformer, Hall sensor, or Kelvin shunt with known ratio, range, bandwidth, phase, insertion effect and calibration. Verify every intended current path passes through the sensor.

Synchronize Before Calculating Power

p(t) = v(t) × i(t)
Pavg = average of p(t) over the declared interval

Voltage and current must share a time base and sign convention. Deskew the channels or include their phase uncertainty. Separate meters with unrelated refresh windows do not provide a reliable dynamic real-power result.

Class-D Bandwidth And Filtering

Class-D switching content can overload an input, alias into the acquisition, alter RMS math, or obscure the audio waveform. State whether the result includes the switching band, uses an external audio analyzer filter, applies a scope bandwidth limit, or uses mathematical filtering. The filter must not hide the clipping or distortion endpoint being evaluated.

Chain Validation

Verify probe and analyzer scaling with a known lower-power source.
Check zero, compensation, deskew and polarity.
Run a protected low-level test through the complete load and measurement path.
Confirm no channel, probe, attenuator, filter or ADC overload.
Repeat the verification after the high-power sequence.