Understanding LM386 Audio Amplifier Gain Calculation
The LM386 is a popular low voltage audio power amplifier designed for use in low voltage consumer applications. Understanding how to control and calculate its voltage gain allows engineers and hobbyists to customize output performance for various speakers and input audio sources. By manipulating the internal feedback path through pins 1 and 8, the gain can be adjusted seamlessly from 20 up to 200.
Formula Used
The default voltage gain ($A_v$) of an LM386 without external components connected between pins 1 and 8 is fixed internally at 20 (which equates to 20 dB). When an external capacitor or resistor-capacitor combination is placed across pins 1 and 8, the internal 1.35 k$\Omega$ resistor is bypassed or modified. The expanded gain formula is approximated as:
$$A_v = 20 + \frac{1250}{R_1}$$
Additionally, the gain in decibels is calculated using logarithmic scaling: $Gain_{dB} = 20 \times \log_{10}(A_v)$. Output power limits are constrained by available supply voltage headroom and load impedance.
How to Use This Calculator
Using this calculation tool is straightforward. First, select your target amplifier gain mode from the configuration options. Input your power supply voltage, load speaker impedance, and input signal level. If you are using custom external components, enter your precise resistor and capacitor values into the respective fields. Finally, click the calculate button to instantly review detailed gain, voltage outputs, and power metrics.