Amplification in MIC with using CMOS 4069

[ikelectro]

View attachment 67102
I'm using this circuit and the out put from pin no.4, I connected it with the clock of 4026. but the problem is I'm getteng some frequency in 4026 when I'm not using the mic. 3digit display shows me 140 to 150(in4026's out put). what should I do to stop the unwanted frequency.



PLZ HELP ME OUT with this problem.

 

[MikeMl]

You have biased the inverters between pins 1 to 4 into the "linear" region to create an amplifier. The open-loop gain between pin 1 and 4 is very high. Even with low audio levels into the mic, the ambient "noise level" is being amplified to the point where it causes the counter to see events.

I would put a pot (~100K) between the coupling cap and Pin 1. You also need a second coupling capacitor between the pot wiper and pin 1. Turn down the gain until the ambient noise no longer advances the counter.

 

[ikelectro]

You have biased the inverters between pins 1 to 4 into the "linear" region to create an amplifier. The open-loop gain between pin 1 and 4 is very high. Even with low audio levels into the mic, the ambient "noise level" is being amplified to the point where it causes the counter to see events.

I would put a pot (~100K) between the coupling cap and Pin 1. You also need a second coupling capacitor between the pot wiper and pin 1. Turn down the gain until the ambient noise no longer advances the counter.

ok then what should be the value for the capling capcitor.???

 

[WTP Pepper]

Vile circuit. You are assuming the centre bias of each individual invertor in the same package is the same. It maybe close, but the second invertor gets its DC bias from the first which is highly unlikely to be the same.
For something the size of a 4069, you can use a decent low noise op-amp and build in a filter. Try a TLO84 instead.

 

[MikeMl]

ok then what should be the value for the capling capcitor.???

same as the existing one (purists would say make them both twice the value of the existing one)

I agree that it is a vile circuit. An OpAmp would do better.

 

[ChrisP58]

While it is possible to trick some digital ICs into working as linear elements, they will never be as good at it as a part that was designed from the beginning to be a linear device.

Unless you are trying to save pennies, and you have a leftover gate from some other logic function, there is really no reason not to use an op-amp for this purpose.

And, if it is a left over part, there will probably be enough crosstalk from the other gates in the package to put a lot of noise into the amplified signal. And that alone may be a source of some of the counts you are seeing.

 

[audioguru]

The first inverter is an inverting type that has a very low input impedance that loads down the output from the mic.
Then the output level from the first inverter is low so the second inverter amplifies it and also amplifies noise.

A non-inverting low noise preamp with a high impedance input should be used. An audio opamp.

The mic should be powered from a 10k resistor from filtered 9V, not from the unfiltered 47k.

The total gain is 400 and the total amplifier is non-inverting so the input from the non-filtered 47k resistor might have some output signal from the power supply. Then the circuit is an oscillator.

 

[ikelectro]

The first inverter is an inverting type that has a very low input impedance that loads down the output from the mic.
Then the output level from the first inverter is low so the second inverter amplifies it and also amplifies noise.

A non-inverting low noise preamp with a high impedance input should be used. An audio opamp.

The mic should be powered from a 10k resistor from filtered 9V, not from the unfiltered 47k.

The total gain is 400 and the total amplifier is non-inverting so the input from the non-filtered 47k resistor might have some output signal from the power supply. Then the circuit is an oscillator.

Any suggestion for the An audio opamp?

 

[audioguru]

Any suggestion for the An audio opamp?

You are in India. I do not know what is available there.
Most of us are in The West where EVERYTHING is available.

I use TL071 single, TL072 dual and TL074 quad audio opamps because they have low noise, extremely low distortion and work well up to 100kHz. Many Western semiconductor manufacturers make them and they are inexpensive.

 

[ikelectro]

i think i can get it.

 

[ikelectro]

You are in India. I do not know what is available there.
Most of us are in The West where EVERYTHING is available.

I use TL071 single, TL072 dual and TL074 quad audio opamps because they have low noise, extremely low distortion and work well up to 100kHz. Many Western semiconductor manufacturers make them and they are inexpensive.

here in india TExas, national, ST etc are also available!!!

 

[ChrisP58]

Texas Instruments was the originator of the TLO series, so you should be good to go with them.

 

[audioguru]

Here we ask and get free samples.