How to use Mute of LM3886 for...

[soundman]

Hello folks,

I have designed an amplifier by a LM3886 to amplify my speech which is fed to the amplifier through a Dynamic microphone and a pre-Amplifier.
I wanna automatically mute the said LM3886 amplifier just whiles I do not talk to the microphone, but as soon as I start to talk to the microphone the lm3886 amplifier turns on and start to work and amplify my voice. That means I want the said amplifier to be turned off while there is no voice-speech and automatically starts to normally work as soon as I talk to the microphone. Is it possible doing so?If so, any method to do that?

Thanks for any help.

 

[alec_t]

Yes, it's possible. One way is to take a pre-amplified mic signal, rectify and smoothe it, then apply the smoothed result to a comparator. The output from the comparator is the mute control signal. Experimentation with the pre-amplification gain, the smoothing time constant and the comparator set-point would be necessary for a good result.

 

[Mr RB]

In professional audo the device is called a "noise gate". Google might get you some schematics. Expanders normally have noise gate function built in, and good compressors or compressor/expanders almost always have noise gating, complete with adjustable cut in/out times etc.

In ham radio a similar device is called "squeltch" and a google of that word may return more info too.

 

[KMoffett]

Also, in radio communications it's referred to as a VOX (voice operated switch...pronounced like "fox" with a V )...Google: VOX circuit

Ken

 

[Mikebits]

To mute the chip you need to remove current from pin 8. After the vox you will need a electrical switch. This tiny part would do it. https://www.electro-tech-online.com/custompdfs/2011/09/MC74VHC1G66-DPDF.pdf

 

[rogs]

You may need to be aware of the one problem that real time 'vox' switching has.
That is the loss of the initial part of the first letter of the first word, every time the switch is activated.
It may not be a significant factor in your application, but for some it's unacceptable.

You can design the 'trigger' circuit to be pretty fast, but you will always lose something. Some word 'first' letters are worse than others.
Probably the most famous example of 'vox' switching loss is Neil Armstrong's first words on the Moon:-

"That's one small step for man, one ' -iant' leap for mankind".

Most of the 'g' of the word 'giant' is missing (G seems to be a particularly difficult letter to deal with, in vox switching).

As I say, may not be a problem, but if it is critical , you can save a lot of effort, by looking to use a manual 'press to talk' switch instead.......

 

[crutschow]

You may need to be aware of the one problem that real time 'vox' switching has.
That is the loss of the initial part of the first letter of the first word, every time the switch is activated.
It may not be a significant factor in your application, but for some it's unacceptable.
.....

To eliminate this an analog delay slightly longer than the VOX operating time (which now can be done with a digital delay A/D and D/A circuit) is added to the audio and the VOX input is taken at the delay line input. This adds a sort of "negative delay" to the VOX circuit, avoiding the cutoff of the first syllable.

 

[rogs]

Yes, a similar approach has been used within the pro audio industry for some time, to deal with a similar problem, in real time compression circuitry.
'Feed forward' compressors are an example.

With the complexity and cost of the required delay circuitry - analogue or digital - likely to be more than all the circuitry of the audio part of the project, it's not often an option for 'basic' vox situations.