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Amplifier Clipping Level

Calculate amplifier clipping voltage, power, and dBV level from supply voltage and load impedance.

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Formula

V_peak ≈ 0.9 × V_cc, P_clip = V_peak² / (2 × Z_L)

V_cc— Supply rail voltage (V)

How It Works

Amplifier clipping occurs when the input signal demands an output voltage or current beyond the amplifier's supply rail capability. As a rule of thumb, the maximum undistorted peak output voltage is approximately 0.85–0.92 × supply rail voltage (the remainder is lost in the output stage transistor saturation voltage and driver losses). For a sinusoidal output, the clipping power is P_clip = V_peak² / (2 × Z_L), where Z_L is the load impedance. The RMS voltage at clipping is V_rms = V_peak / √2. The clip level in dBV = 20·log₁₀(V_rms). Understanding the clipping threshold is critical for system design: audio signals are programme material with a crest factor (peak-to-RMS ratio) of 10–20 dB. An amplifier rated at 100 W continuously will clip on transient peaks from a signal with programme level set only 3 dB below rated power.

Worked Example

Amplifier: ±18 V dual supply (36 V rail-to-rail). Load: 8 Ω. Max output voltage (using 0.9 × V_supply): V_peak = 0.9 × 18 = 16.2 V peak RMS voltage at clipping: V_rms = 16.2 / √2 = 11.46 V RMS Clipping power: P_clip = (16.2)² / (2 × 8) = 262.4 / 16 = 16.4 W Clipping level in dBV: dBV = 20·log₁₀(11.46) = 21.2 dBV With 100% headroom reserve (no reduction): max clean output = 16.4 W into 8 Ω. Reducing headroom reserve to 70% reduces max clean output by 20·log₁₀(0.7) ≈ −3.1 dB in voltage, and power to 16.4 × 0.7² ≈ 8 W — providing additional margin before clipping.

Practical Tips

  • ✓Add 10 dB of headroom above typical listening level to avoid clipping on transients. If your typical listening level at the speaker is 90 dB, the amplifier should handle 100 dB peaks without clipping — requiring roughly 10× more peak power than average power.
  • ✓Soft clipping (gentle saturation before hard clipping) is less audibly harsh than hard clipping. Some amplifier designs include soft-clip circuits or limiters before the output stage to manage graceful overload.
  • ✓Monitor clip indicators on amplifiers and mixers during installation and setup. Consistent clipping at moderate signal levels indicates either gain staging is too high (turn down input trim) or the amplifier is undersized for the speaker/room combination.

Common Mistakes

  • ✗Confusing clipping power with continuous rated power — an amplifier rated at '100 W RMS' is tested with a sine wave at clipping threshold. In real use with programme material, the amplifier will clip transiently on peaks when programme level averages only 10–20 W (due to the high crest factor of music).
  • ✗Assuming both channels never clip simultaneously — stereo amplifiers share a power supply. On loud bass transients, both channels draw peak current simultaneously, causing supply sag and lowering the effective clipping voltage below the idle value.
  • ✗Not accounting for loudspeaker impedance dips — speaker impedance varies with frequency. A nominal 8 Ω speaker may dip to 3–4 Ω at certain frequencies, doubling the demanded current and dropping the effective clipping power.

Frequently Asked Questions

A clipped waveform is rich in high-order harmonics — a clipped sine wave at 100 Hz produces strong components at 300 Hz, 500 Hz, and up through the tweeter frequency range. These high-frequency harmonics carry significant energy to the tweeter, which was not designed for that power level, causing thermal damage to the voice coil. Hard clipping is the most common cause of blown tweeters.
The most reliable method is oscilloscope measurement of the output waveform — look for the tops of sine waves becoming flat. Audible signs include harshness or 'buzzing' on peaks, especially on sustained notes. Many amplifiers include clip LEDs triggered when the output nears the supply rail. Limiters in professional audio systems prevent clipping by reducing gain before the output reaches the rail.
Yes. The headroom reserve (0–100%) scales the operating peak output voltage linearly relative to the theoretical maximum. At 100%, the amplifier is at the edge of clipping. At 70%, you have ~3 dB of headroom before clipping. This is useful for system design to ensure transient peaks don't clip: set operating level to 50–70% of clip threshold for typical programme material.

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