Best Way to Amplify Capacitive Microphone Output—Is LM386 Suitable?

147 13

#1 21676821 19 Dec 2016 13:56

reyhane mohebali reyhane mohebali

Anonymous

Post #1
21676821 19 Dec 2016 13:56

Hello,

I want to amplify the output of a capacitive microphone, what's the best way for doing this?

Can LM386 be a good choice?

please help me, tnx.
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#2 21676822 19 Dec 2016 20:29

Kevin Angelo Ma Kevin Angelo Ma

Anonymous

Post #2
21676822 19 Dec 2016 20:29

By how much do you want to amplify the output? Also, wouldn't any audio amplifier work?
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#3 21676823 20 Dec 2016 01:08

reyhane mohebali reyhane mohebali

Anonymous

Post #3
21676823 20 Dec 2016 01:08

I need 100 gain voltage,
I have tested the suggested circuits in LM386 datasheet, but it didn't work!
#4 21676824 20 Dec 2016 01:49

Dean Franks Dean Franks

Anonymous

Post #4
21676824 20 Dec 2016 01:49

Does the microphone you are using have an internal FET amplifier or is it a raw electret element?

If you search for "rode amplifier design" on youtube you can view a series of videos (EEVBlog) done by an experienced engineer on how to design very high performance microphone amplifiers.
#5 21676825 20 Dec 2016 16:30

reyhane mohebali reyhane mohebali

Anonymous

Post #5
21676825 20 Dec 2016 16:30

My microphone doen't have any FET amplifier,
I have read that the maximum voltage that a microphone can produce, is 50mv. I want to increase this voltage to 5 volt.
What should I do?
#6 21676826 20 Dec 2016 16:35

Dean Franks Dean Franks

Anonymous

Post #6
21676826 20 Dec 2016 16:35

There are lots of potential solutions and choosing the right one requires detailed knowledge about what you are trying to accomplish. You can optimize for low noise, high dynamic range, low distortion or low power usage.

Take a look at:
https://sites.google.com/a/vt.edu/amp_lab/pro...s/high-gain-low-noise-microphone-preamplifier

For a good high gain design and a detailed discussion of the design issues.
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#7 21676827 26 Dec 2016 16:49

reyhane mohebali reyhane mohebali

Anonymous

Post #7
21676827 26 Dec 2016 16:49

thanks, I have LM386 amplifier, but when I use its suggested circuit for 200 gain,
I don't achieve the expected result
What would the problem be?
Should I use a preamplifier? If yes, which preamplifier?!
#8 21676828 17 Jan 2017 18:33

Jeff Gray Jeff Gray

Anonymous

Post #8
21676828 17 Jan 2017 18:33

I have done this many times. Ideally, you may need another component ahead of the LM386, depending on your microphone, but maybe not. Can you tell me more detail about what kind of microphone element you have? Does it have two wires or 3?
#9 21676829 17 Jan 2017 23:31

Sambath Kumar Sambath Kumar

Anonymous

Post #9
21676829 17 Jan 2017 23:31

Hi Reyhane mohebali ,

pl ref my attachment it will help you.

Regards V.Sambath kumar.
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#10 21676830 18 Jan 2017 02:16

reyhane mohebali reyhane mohebali

Anonymous

Post #10
21676830 18 Jan 2017 02:16

It's a capacitor microphone and has two wires
#11 21676831 18 Jan 2017 10:14

Jeff Gray Jeff Gray

Anonymous

Post #11
21676831 18 Jan 2017 10:14

Are you supplying the mic with a bias voltage? It needs and applied voltage in order for sound waves to make a signal. Without a bias it won't do anything.
#12 21676832 18 Jan 2017 11:22

Jeff Gray Jeff Gray

Anonymous

Post #12
21676832 18 Jan 2017 11:22

That would work... Or you should be able to use your LM386, like this (see attachment)
#13 21676833 19 Jan 2017 08:50

reyhane mohebali reyhane mohebali

Anonymous

Post #13
21676833 19 Jan 2017 08:50

I can't get the image, Would you please send it to my email?
#14 21676834 20 Jan 2017 00:18

Jeff Gray Jeff Gray

Anonymous

Post #14
21676834 20 Jan 2017 00:18

I can't figure out how to do that on this forum, but it's a really simple circuit. Starting from left side...

9v Battery has + terminal at top and - terminal at bottom.
- terminal goes to ground.
+ terminal goes to + wire of microphone and to pin 6 of LM386
- terminal of microphone goes down to top of potentiometer(100kohm).
Bottom of potentiometer goes to ground.
Wiper of potentiometer goes to pin 3 of LM386
pin 2 of LM386 goes to ground
pin 4 of LM386 goes to ground
pin 7 of LM386 is not connected
between pin 1 and 8 of LM386 is a 10uF cap with +terminal on pin 1
pin 5 of LM386 goes to + terminal of 100uF coupling cap
- terminal of that 100uf cap goes to speaker/headphone.
other terminal of speaker goes to ground
also from pin 5 of LM386 is the plus side of 0.05uF cap
- side of that .05uF cap goes to top of 10 ohm resistor
bottom of 10ohm resistor goes to ground.

100kohm pot can be any value from 10kohm to 100k. If you don't have a pot, you can just put in a 100kohm resistor, but then you'll have no volume control.

Also, the .05uF cap and 10 ohm resistor are just there to eq out high frequency/hiss, so you can probably leave them out just for testing the circuit.

Hope this helps.
J
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Topic summary

✨ The discussion focuses on amplifying the output of a capacitive (condenser) microphone, which typically produces a maximum voltage around 50mV, with the goal of achieving approximately 5V output, implying a voltage gain near 100. The LM386 audio amplifier was tested using its datasheet circuits for gains up to 200, but did not yield the expected results. Key considerations include whether the microphone has an internal FET amplifier or is a raw electret element; in this case, the microphone lacks an internal FET and has two wires. Proper biasing of the microphone with a DC voltage is essential for operation. Suggestions include using a dedicated low-noise microphone preamplifier stage before the LM386 or alternative high-gain low-noise amplifier designs. A detailed LM386-based circuit was described, involving a 9V supply, biasing the microphone through a potentiometer (10k–100k), and specific capacitor and resistor connections to achieve amplification. References to external resources such as EEVBlog videos on Rode amplifier design and a high-gain low-noise microphone preamplifier project were provided for further guidance.

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Best Way to Amplify Capacitive Microphone Output—Is LM386 Suitable?

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]