FAQ
TL;DR: A simple 9 V LM386 build can amplify a two‑wire capacitive mic; “100kohm pot can be any value from 10kohm to 100k,” and add 10 µF between pins 1–8 for high gain. [Elektroda, Jeff Gray, post #21676834]
Why it matters: This FAQ shows how to power, bias, and wire a raw electret/capacitive mic so your LM386 build actually delivers usable audio.
For: Hobbyists and students asking “what’s the best way to amplify a capacitive mic, and is LM386 OK?”
Quick Facts
- Two‑wire capacitive/electret mics require bias; without it they produce no output. [Elektroda, Jeff Gray, post #21676831]
- Target example: 50 mV mic level to 5 V requires ~100× voltage gain. [Elektroda, reyhane mohebali, post #21676825]
- LM386 high‑gain wiring: 9 V supply, 10 µF between pins 1–8, ~100 µF output cap, 0.05 µF+10 Ω Zobel, 10–100 k input pot. [Elektroda, Jeff Gray, post #21676834]
- Users often chase “200×” LM386 gain from datasheet circuits; stability and input biasing still matter. [Elektroda, reyhane mohebali, post #21676827]
- Raw electret elements differ from capsules with internal FET buffers; the choice affects preamp needs. [Elektroda, Dean Franks, #21676824
Is the LM386 suitable for amplifying a capacitive/electret microphone?
Yes, if you bias the mic and follow correct LM386 input and gain wiring. A two‑wire capsule can feed pin 3 via a volume pot, with 10 µF across pins 1–8 for higher gain. “You should be able to use your LM386, like this.” [Elektroda, Jeff Gray, post #21676832]
Do I need a preamplifier before the LM386?
Sometimes. It depends on the microphone element and your goals (noise, dynamic range, distortion, power). An additional front‑end may be required for very low‑noise work or raw elements. Ask yourself what you’re optimizing for before choosing. [Elektroda, Dean Franks, post #21676826]
How much gain do I need to turn 50 mV into about 5 V?
About 100× voltage gain. That takes a typical small mic signal near 50 mV and lifts it to around 5 V peak, assuming headroom and clipping are managed downstream. [Elektroda, reyhane mohebali, post #21676825]
Why didn’t the LM386 “200× gain” circuit work for my mic?
A common failure is missing mic bias. Without bias, a two‑wire electret outputs nothing, so the LM386 only amplifies noise. Confirm biasing first, then check wiring and grounding. “Without a bias it won’t do anything.” [Elektroda, Jeff Gray, post #21676831]
How do I bias a two‑wire capacitive/electret microphone?
Provide a DC supply to the mic through the designated lead, then route the mic return through your volume pot to the LM386 input. The post emphasizes that the capsule needs applied voltage to generate a signal at all. [Elektroda, Jeff Gray, post #21676831]
Quick 3‑step: how do I wire the LM386 for a mic test?
- Power: 9 V battery + to mic + and LM386 pin 6; − to ground.
- Input: Mic − to top of 10–100 k pot; pot wiper to pin 3; pin 2,4 to ground.
- Gain/output: 10 µF between pins 1–8; pin 5 via 100 µF to load; optional 0.05 µF//10 Ω to ground. [Elektroda, Jeff Gray, post #21676834]
What value should I use for the input volume pot?
Use 10 k–100 k. As the expert notes, “100kohm pot can be any value from 10kohm to 100k.” Start at 50 k if unsure, then tweak for noise and level. [Elektroda, Jeff Gray, post #21676834]
What do LM386 pins 1 and 8 do for microphone use?
They set gain. Adding a 10 µF capacitor between pins 1 and 8 drives the LM386 into its high‑gain mode, useful when boosting small mic signals. Observe polarity as shown. [Elektroda, Jeff Gray, post #21676834]
What’s the difference between a raw electret element and one with an internal FET?
A raw element needs external bias and has high source impedance. Capsules with an internal FET buffer behave like low‑impedance sources and are easier to amplify. Identify which you have before choosing a circuit. [Elektroda, Dean Franks, post #21676824]
Where can I see a high‑gain, low‑noise mic preamp example?
Check the referenced high‑gain, low‑noise microphone preamplifier design and explanation provided in the discussion. It covers design trade‑offs for noise and dynamic range. [Elektroda, Dean Franks, post #21676826]
Can the LM386 really do 200× gain?
Yes, that’s a common datasheet mode discussed in the thread. However, high gain amplifies noise and layout issues; biasing and filtering become critical. Stabilize the input and keep leads short. [Elektroda, reyhane mohebali, post #21676827]
What output components should I use for cleaner sound?
Use a 100 µF coupling capacitor from pin 5 to your load. Add a small 0.05 µF capacitor in series with a 10 Ω resistor from pin 5 to ground as a Zobel to tame hiss. [Elektroda, Jeff Gray, post #21676834]
Can I drive headphones or a small speaker directly from the LM386?
Yes. Route pin 5 through a 100 µF electrolytic to the headphone or speaker, with the other lead to ground. Keep volumes modest during testing to avoid clipping and hearing damage. [Elektroda, Jeff Gray, post #21676834]
Do I need to connect LM386 pin 7 (bypass)?
Not required in the shared build. The reference wiring leaves pin 7 unconnected and works for a basic mic amplifier test. Add bypass later if you chase noise performance. [Elektroda, Jeff Gray, post #21676834]
What supply should I start with for a quick prototype?
A 9 V battery is convenient and matches the reference wiring. It keeps the setup portable and reduces hum while you validate bias and gain. [Elektroda, Jeff Gray, post #21676834]
