◀ Back to Note

Tony's Intertwingled Memex • Reference Manual

Audio Pre-Amplifier Hard Limiting (Electrical & Audio Engineering)

Formulas & Definitions

In live sound and broadcast engineering, a high-gain audio pre-amplifier circuit boosts an incoming microphone input voltage vvv (in Volts). To prevent power amplifier overload and speaker cone burnout during acoustic feedback spikes, the amplified signal passes through a multi-stage non-linear compression and hard-limiting saturation circuit.

The total output voltage Vout(v)V_{\text{out}}(v)Vout​(v) as a function of the input surge voltage vvv is modeled by the composite function:

Vout(v)=5⋅tan⁡−1(ln⁡(1+ev))V_{\text{out}}(v) = 5 \cdot \tan^{-1}\left(\ln\left(1 + e^v\right)\right)Vout​(v)=5⋅tan−1(ln(1+ev))

As a sudden electrostatic discharge or feedback loop causes the microphone input voltage to surge toward infinity (v→∞v \to \inftyv→∞):

  1. Use the multi-stage inside-out composite limit technique to evaluate lim⁡v→∞Vout(v)\lim_{v \to \infty} V_{\text{out}}(v)limv→∞​Vout​(v).
  2. Determine whether the output signal clamps at a finite voltage threshold, and state the maximum output voltage delivered to downstream audio speakers.