low noise mic amplifier

[easy electronics]

I need HELP to make a low noise amplifier circuit to amplify MIC signal.

i want to amplify mic signal and give them to speaker .

MIC --> LOW NOISE AMPLIFIER -->> SPEAKERS.

i have tried lm386 but it gives too much noise .

 

[kam1787]

that is a little vague
hi or low impedance mic?
op-amp or discrete?
I guess a single ended power supply..........

the 386 is HORRIBLE!

BTW the usual arrangement is a pre-amp feeding an amp feeding speakers

do you want stereo? you did say speakerS or it is a 2-way or 3-way speaker?
how many watts [rms]?

is noise your only criteria? not distortion? not efficiency? not price? not simplicity?

this is a discrete single ended low noise mic pre-amp **broken link removed**

 

[Audioguru]

If the microphone can hear the speaker then you will have acoustical feedback howling.
Start with the microphone. Is it an electret type that has a Jfet inside and it needs to be powered or is it a dynamic type with a coil and magnet like a small speaker?
The mic needs a low noise preamp. An LM386 is not low noise and is not a preamp, it is a power amp. There are many low noise audio opamps available that make an excellent preamp.
Decide how much power you need into a speaker and select a suitable power amp IC. The preamp feeds the power amp with a volume control in between.

 

[easy electronics]

Basically i want to make noise cancelling headphone
using arduino due board

 

[KlausST]

Hi,

You didn't answer the questions.
If you want a low noise amplifier you first need to know about the microphone. Especially it's impedance.
Then one can decide if a fet input opamp or a bjt input opamp is suitable.

Then some parameters like gain, bandwidth, output power... are of interest


Klaus

 

[easy electronics]

i am going to pull MIC from any circuit . :fight:
now please tell me which device i should destroy to pull mic. headphone , laptop mic
or this one i should use for noise cancelling project.



i am going to
amplify mic signal >> arduino due >>dac >> amplifier >> speaker

 

[Audioguru]

Your electret mic is pretty big. I got one from a damaged cell phone that is half that size.

 

[godfreyl]

Basically i want to make noise cancelling headphone
using arduino due board

1) There's no reason to use an arduino or any kind of microprocessor.
2) Before starting the circuit design, you need to know how noise-cancelling headphones work. e.g. that the microphone goes inside the headphone, in the cavity between the loudspeaker and your ear. Also the frequency response of the elecronics has to be tailored to avoid instability - you don't want anything like a flat response for the mic, more like a first order low-pass filter with a low corner frequency maybe around 1Hz or lower.
3) TL071 is probably good enough for the mic preamp.

 

[Audioguru]

the microphone goes inside the headphone, in the cavity between the loudspeaker and your ear.

Sounds like a recipe for acoustical feedback howling.
Usually a noise cancelling headphone has its microphone mounted OUTSIDE the cavity so that it picks up background noise but does not pickup the signal you want.

 

[godfreyl]

Sounds like a recipe for acoustical feedback howling.

Feedback, yes, but the idea is to use negative feedback to reduce the ambient noise inside the headphone cup. As with any other negative feedback system, you have to pay attention to the loop gain and phase to avoid instability and oscillation.

Usually a noise cancelling headphone has its microphone mounted OUTSIDE the cavity so that it picks up background noise but does not pickup the signal you want.

That can work too but, IMHO, the equalisation is much trickier. For effective cancellation, you need to closely match the amplitude and phase of the "anti-noise" generated inside the cup with the amplitude and phase of the outside noise leaking in.

Anyway, both approaches are summed up in this patent:

The noise-canceling headphones are equipped with: a microphone installed in a housing to receive ambient noise components generated around the headphones; and noise-reducing circuitry to generate signals with the opposite polarity of the ambient noise components, combine the opposite-polarity signals with audio signals, and output the combined signals through speakers. The noise-canceling headphones are thus active headphones that make listeners feel that noises are reduced with “opposite-polarity cancellation effects” to the ambient noises.

Another type of known noise-canceling headphones is equipped with: a microphone provided between an ear of a user and a speaker to directly receive sounds that include ambient noises components and are to be given off to the ear; and feedback noise-reducing circuitry to detect the ambient noises components from the difference between the received sounds and an original signal and output audio signals from which the ambient noises components are subtracted, thus reducing the ambient noises components.

The former using the opposite-polarity cancellation effects is called a feed forward type whereas the latter using the feedback circuitry is called feedback type.

 

[Audioguru]

I think the phase of the speakers in headphones is all over the place and would be very difficult or impossible to cancel to avoid feedback. The phase of the electret microphone is very constant at most frequencies so cancelling ambient noise with the mic mounted outside the headphone is easy.

Sony has DIGITAL noise-cancelling headphones with microphones inside and outside the ear cup. They cost "only" $500.00.

 

[easy electronics]

Thank's everyone
i have made this circuit and this is amplifying mic signal without noise .

 

[Audioguru]

The 0.1uF capacitor C3 cuts all frequencies above only about 2000Hz. Then the sound will be VERY muffled so of course you will not hear noise. Audio goes to 20,000Hz.
But then noise cancelling headphones cancel only low frequencies so your circuit will be fine.

 

[KlausST]

Hi,

good point, audioguru,

in in addition, the capacitor is not only killing the higher frequencies, but it adds a phase shift.
Especially for noise cancelling the phase shift may cause problems.

Here a higher order and also higher cutoff frequency low pass filter may improve performance.
Look for filters with low frequency shift in the pass band area.

Klaus

 

[Audioguru]

I had my hearing tested recently. I went into a soundproof room that sounded like I died in there then the pretty young audiologist put the earphones on me and I could not hear ANYTHING except the test tones and her s*** voice softly saying sear, beer, gear, leer, fear, dear etc. The test showed that my sensitivity to hear high audio frequencies isn't what it was 55 years ago when I could hear ultrasonic burglar alarms. The Danish demo $5500.00 hearing aids I wore for 10 days sounded awful and squealed with feedback so I got another hearing test at a different place showing much less loss and now I have very nice sounding Swiss demo $5540.00 hearing aids for 3 months. One mode has noise reduction something like what Dolby did with cassette recordings. Multiple directional microphones also cancel noise. Music sounds wonderful again.