i am a bit confuse about this. if every RC network have same cutoff frequency, why can not use same value of RC since the calculation will get back the same cutoff frequency?

The input resistance of the preamp is 50k ohms because it has two 100k resistors biasing it.
The input resistance of the tone controls circuit is 100k ohms so its input coupling capacitir has a smaller value than the preamp. But its resistor values can easily be reduced to use the same capacitor value.
Maybe you cannot find a 50k ohms volume control then its input capacitor value must be re-calculated.
The input resistance of the LM386 amp is typically 50k ohms so it can use the same value coupling capacitor as the input of the preamp.
But what about the capacitor that feeds the low resistance of the earphones? Its value will be much higher than the others.

For the 3-way tone controls, all power supply pin have to decoupled with 10uF and 0.1uF capacitor, i know that the +ve pin should connect to 0.1uF capacitor, but how about the 10uF, where should i connect it?

The 10uf capacitor filters low frequencies and the 0.1uf capacitor filters high frequencies. They are connected in parallel so that all frequencies are filtered from the supply.

I try this 3-way tone controls in stimulator, but i am not sure how it work, is that each band of pontentiometer is use to control the amplitude(peak-to-peak) of particular frequency?

The pot adjusts how much gain (boost) or loss (cut) there is in the bandwidth of the filter.

 

The input resistance of the preamp is 50k ohms because it has two 100k resistors biasing it.

previously the RC network in pre-amp was 4.7k ohm and 47nF, but due to whole circuit have more than 1 RC network,so have to recalculate the RC value? May i know how you calculate it is 50k ohms due to two 100k resistors but not other value? Is that mean that if my bias resistor is 50k, then the input resistance in preapmp should be half of it which is 25k?

The input resistance of the tone controls circuit is 100k ohms so its input coupling capacitir has a smaller value than the preamp. But its resistor values can easily be reduced to use the same capacitor value.
Maybe you cannot find a 50k ohms volume control then its input capacitor value must be re-calculated.
The input resistance of the LM386 amp is typically 50k ohms so it can use the same value coupling capacitor as the input of the preamp.
But what about the capacitor that feeds the low resistance of the earphones? Its value will be much higher than the others.

i have attach 2 picture which is about RC, i have some question:
1) RC network is connect like the pic1.1 right? And this connection will cut the high frequency?(similar to lowpass filter)
2)the pic1.2 should be a CR network which will cut the low frequency( similar to high pass filter)

Then both of the network should have difference cutoff frequency ? (due to 1 is cut the high frequency and for another is cut the low frequency)

If we want to calculate the total cutoff frequency, so it will be 2 type of cutoff frequency which is high cutoff and low cutoff frequency?

The input resistance of the tone controls circuit is connected like the attachment pic 2.3, was that a RC network too? it will have a high cutoff frequency or small cutoff frequency?

Thanks!

 

previously the RC network in pre-amp was 4.7k ohm and 47nF

No.
The 4.7k resistor is not the input resistance of the preamp that is fed from the input coupling capacitor. The 4.7k resistor applies power to the Jfet transistor inside the electret mic.
The input resistance of the mic preamp is the two 100k resistors in parallel that bias it. The output resistance of the mic is in parallel with the 4.7k resistor (resulting in a total of about 3k ohms) and are in series with the 50k input resistance of the preamp. So the R of the RC is about 53k ohms.

due to whole circuit have more than 1 RC network,so have to recalculate the RC value?

Yes.

May i know how you calculate it is 50k ohms due to two 100k resistors but not other value?

The two resistors that bias the opamp in the preamp are in parallel to the signal. Their values must be the same and can be from 1k ohms to 1M ohms. We have selected 100k ohms each.

Is that mean that if my bias resistor is 50k, then the input resistance in preapmp should be half of it which is 25k?

If the total R is 25k then it is used in the calculation of the capacitor for a certain cutoff frequency.

I have attach 2 picture which is about RC, i have some question:
1) RC network is connect like the pic1.1 right? And this connection will cut the high frequency?(similar to lowpass filter)

2) The pic1.2 should be a CR network which will cut the low frequency( similar to high pass filter)

Yes and yes.

Then both of the network should have difference cutoff frequency ? (due to 1 is cut the high frequency and for another is cut the low frequency)

Each can have any cutoff frequency. If they are in series and are buffered so they do not affect each other and both have the same cutoff frequency then they make a bandpass filter but their peak is attenuated.

If we want to calculate the total cutoff frequency, so it will be 2 type of cutoff frequency which is high cutoff and low cutoff frequency?

An RC lowpass filter that is buffered then is feeding a CR highpass filter have gradual slopes so are never used as a bandpass filter.

The input resistance of the tone controls circuit is connected like the attachment pic 2.3, was that a RC network too? it will have a high cutoff frequency or small cutoff frequency?

The input opamp in the tone controls circuit is inverting so its input resistance is the value of the resistor that feeds it. The capacitor in series with this resistor forms a highpass filter with it. Since R is 100k ohms then for a cutoff frequency of 10Hz the value of C must be 0.16uF. The 100k resistor must have the same value of the feedback resistor for the level gain to be 1 and their value can be changed for you to use the same coupling capacitor value as most of the other RC networks in this project.

 

No.
The input resistance of the mic preamp is the two 100k resistors in parallel that bias it. The output resistance of the mic is in parallel with the 4.7k resistor (resulting in a total of about 3k ohms) and are in series with the 50k input resistance of the preamp. So the R of the RC is about 53k ohms.

Sorry for my poor understanding, previously i was connected my mic just like the attachment pic, was it correct? do you mean that C1 is the coupling capacitor and the R in RC network is the two 100k resistors(R5 and R8) in parallel that bias it? Or should i need to add 1 more resistor with 53k ohm to form a RC? ( C1 value need to change according to the 53k ohm ?)

Each can have any cutoff frequency. If they are in series and are buffered so they do not affect each other and both have the same cutoff frequency then they make a bandpass filter but their peak is attenuated.

If they have same cutoff frequency (example 50Hz), then it will have a narrow peak of 50Hz if form as bandpass( lowpass cut the frequency that more than 50Hz and highpass cute the frequency that below 50Hz) It should affect my circuit signal if whole circuit contain RC and CR network with same cutoff frequency which only allow50Hz to pass through? so it should not have same cutoff frequency?(example for RC,total cutoff frequency should set to 20kHz while for CR, total cutoff frequency set to around 50Hz?)

I am confuse about RC network since RC cut the frequency that higher than it's cutoff frequency, why we need to set the total cutoff frequency to 50Hz instead of 20kHz?


Thanks!

 

Sorry for my poor understanding, previously i was connected my mic just like the attachment pic, was it correct?

Yes.

do you mean that C1 is the coupling capacitor and the R in RC network is the two 100k resistors(R5 and R8) in parallel that bias it? Or should i need to add 1 more resistor with 53k ohm to form a RC? ( C1 value need to change according to the 53k ohm ?)

R5 and R8 in parallel are 50k. R1 is 4.7k and is in parallel with the impedance of the mic and their total is about 3k which is in series with the 50k of the resistors so their total is 53k.

If they have same cutoff frequency (example 50Hz), then it will have a narrow peak of 50Hz if form as bandpass( lowpass cut the frequency that more than 50Hz and highpass cute the frequency that below 50Hz) It should affect my circuit signal if whole circuit contain RC and CR network with same cutoff frequency which only allow50Hz to pass through? so it should not have same cutoff frequency?(example for RC,total cutoff frequency should set to 20kHz while for CR, total cutoff frequency set to around 50Hz?)

Use a bandpass filter circuit for a narrow bandpass, not a lowpass plus a highpass. But you don't want a narrow bandpass do you?

I am confuse about RC network since RC cut the frequency that higher than it's cutoff frequency, why we need to set the total cutoff frequency to 50Hz instead of 20kHz?

The coupling capacitors and their load resistances are highpass filters that cut low frequencies. For voices you want the low cutoff frequency to be 50Hz and the high cutoff frequency to be as high as you can make it or at least 14kHz.

 

R5 and R8 in parallel are 50k. R1 is 4.7k and is in parallel with the impedance of the mic and their total is about 3k which is in series with the 50k of the resistors so their total is 53k.

So i just need to change the C1 to 0.33uF (calculated value is 0.3uF),then others are remain as same?

Use a bandpass filter circuit for a narrow bandpass, not a lowpass plus a highpass. But you don't want a narrow bandpass do you?

Because the input of tone control have a capacitor and resistor in series,so i am not sure whether that is consider as a CR network or not, and there have a RC network connected in the input of preamp, so i was thinking is that it will form a bandpass filter since there have a RC in input of pre-amp and CR in output of preamp?

The coupling capacitors and their load resistances are highpass filters that cut low frequencies. For voices you want the low cutoff frequency to be 50Hz and the high cutoff frequency to be as high as you can make it or at least 14kHz.

Do you mean that the RC network that connected in the input of preamp should be a CR network which cut the low frequencies? So it should be connected like pic1.2 instead of 1.1?

Thanks!

 

So i just need to change the C1 to 0.33uF (calculated value is 0.3uF),then others are remain as same?
Each one should be calculated by itself. 0.33uF for this one will be fine for this coupling capacitor.

Because the input of tone control have a capacitor and resistor in series,so i am not sure whether that is consider as a CR network or not, and there have a RC network connected in the input of preamp, so i was thinking is that it will form a bandpass filter since there have a RC in input of pre-amp and CR in output of preamp?

You should be able to simply look at a CR network to see if it is a lowpass filter or a highpass filter. The input of the preamp has a coupling caspacitor which is part of a highpass filter and the output has another highpass filter. There is no lowpass filter.
A simple bandpass filter has both.

Do you mean that the RC network that connected in the input of preamp should be a CR network which cut the low frequencies? So it should be connected like pic1.2 instead of 1.1?

Why can't you see that C1 feeding the biasing resistors of the opamp make a highpass filter?

 

You should be able to simply look at a CR network to see if it is a lowpass filter or a highpass filter. The input of the preamp has a coupling caspacitor which is part of a highpass filter and the output has another highpass filter. There is no lowpass filter.
A simple bandpass filter has both.

sorry about that , because normally when i saw RC network, i will straight away think that it should be a RC network( lowpass) and same for CR network (highpass),so when you mention about RC, i will think that should be a lowpass..

So other Coupling capacitor that feed in this circuit should be CR network( highpss) instead of RC?

Thanks!

 

So other Coupling capacitor that feed in this circuit should be CR network( highpss) instead of RC?

The circuit does not have any lowpass filters. All the coupling capacitors make highpass filters.

 

The circuit does not have any lowpass filters. All the coupling capacitors make highpass filters.

hi, below is my equalizer circuit,I have some question want to ask:

1) when i use signal generator to generate a frequency of 100Hz as input,where should i measure the signal for each band as show in the diagram with difference colour of circle?

2) I use oscilloscope to measure the output signal with 100Hz input,when i set all potentiometer to 0% except R4 and only adjust the R4 capacitor which is bass( because my input is low frequency) , i found out that when i increase the potentiomer value from 0% to certain value, my signal amplitude will increasing ( for CH2[output of bass] and CH3[output of tone control]), but when i set R4 to 0% while increasing the R5 ( which is middle frequency) it will also increase the amplitude of both output. The second pic show that when it is 0% for all 3 pontentiometer and third picture show that when i adjust my middle frequency pontentiometer to 70% and the amplidue for the output of bass channel (CH2) and output of tone control (CH3) was increase.

Is that the middle frequency control will affect the bass and also the treble tone?

Thanks!

 

You don't have an equalizer. Instead you have 3-band tone controls.
An equalizer has adjustable frequency bands or many frequency bands.

Why don't you understand that your opamps are not biased correctly?
Your opamps have their inputs biased at ground so they act like rectifiers and might be destroyed. The inputs must be biased at half the supply voltage with two resistors as a voltage divider and a filter capacitor. Then the outputs will be at half the supply voltage so they can swing up and down making AC.

The filters are very simple and have gradual slopes. If the mid-frequencies control is turned down all the way (-20dB which is 1/10th the output) then the bass control will affect the output a little when the signal is 1kHz. If the bass control is turned down all the way (-20dB which is 1/10th the output) then the mid-frequencies control will affect the output a little when the frequency is 100Hz. The mid-frequency control affects high frequencies a little and the high frequency control affects mid-frequencies a little.

The opamps are inverting so the signal levels at the (-) inputs are almost zero because the opamps have extremely high gain and the negative feedback cancels most signal at the (-) inputs.

 

You don't have an equalizer. Instead you have 3-band tone controls.
An equalizer has adjustable frequency bands or many frequency bands.

May i know the different between equalizer and 3-band tone controls is the numbers of frequency bands only?

Why don't you understand that your opamps are not biased correctly?
Your opamps have their inputs biased at ground so they act like rectifiers and might be destroyed. The inputs must be biased at half the supply voltage with two resistors as a voltage divider and a filter capacitor. Then the outputs will be at half the supply voltage so they can swing up and down making AC.

Because i want to separately test the 3-band tone controls,so i am not connect it with the pre-amp, in my input of pre-amp already have biased at half the supply voltage, may i know i still need to add a bias voltage before the input of tone controls? Or i just need a to add for the separate testing need, if i not connect with pre-amp?

The filters are very simple and have gradual slopes. If the mid-frequencies control is turned down all the way (-20dB which is 1/10th the output) then the bass control will affect the output a little when the signal is 1kHz. If the bass control is turned down all the way (-20dB which is 1/10th the output) then the mid-frequencies control will affect the output a little when the frequency is 100Hz. The mid-frequency control affects high frequencies a little and the high frequency control affects mid-frequencies a little.

May i know, if i have a input frequency of 100Hz, then it consider as bass band, so i just need to adjust the potentiometer in the bass band while others band of potentiomter are remain 0%? But since human voice are not just remain on certain frequency, how to adjust it for these frequency?

Thanks!

 

Hello,

If you want to know more about the equalizers, read this page:
http://stereos.about.com/od/introductiontostereos/a/equalizers.htm

Bertus

 

May i know the different between equalizer and 3-band tone controls is the numbers of frequency bands only?

Did you look at Hearing Aid in Google?
Many older hearing aids are analog and some have 20 fixed bands of frequencies or they are built with only a few fixed frequency bands with only the frequency bands that are needed.
Many new hearing aids are digital and also have 20 adjustable frequency bands that can be re-programmed by the ear doctor if required.
Tone controls have only 2 or 3 frequency bands. My stereo has only bass and treble tone controls that I have never used because the frequency balance is perfect without making changes.

Because i want to separately test the 3-band tone controls,so i am not connect it with the pre-amp, in my input of pre-amp already have biased at half the supply voltage, may i know i still need to add a bias voltage before the input of tone controls?

The opamps in the tone controls circuit do not work properly when they are biased wrong. Maybe your simulation program does not know it.

May i know, if i have a input frequency of 100Hz, then it consider as bass band, so i just need to adjust the potentiometer in the bass band while others band of potentiomter are remain 0%? But since human voice are not just remain on certain frequency, how to adjust it for these frequency?

The simple tone controls circuit adjusts wide bands of frequencies. It does not help a deaf person can hear much better. It just adjusts only 3 frequency bands with gradual slopes so the bands affect each other. It is a "pretend" hearing aid but it might work fine for a few deaf people.

 

Did you look at Hearing Aid in Google?
Many older hearing aids are analog and some have 20 fixed bands of frequencies or they are built with only a few fixed frequency bands with only the frequency bands that are needed.
Many new hearing aids are digital and also have 20 adjustable frequency bands that can be re-programmed by the ear doctor if required.
Tone controls have only 2 or 3 frequency bands. My stereo has only bass and treble tone controls that I have never used because the frequency balance is perfect without making changes.

yes, i do search from google, but i really cant find any topic which relate the hearing aids with equalizer. Normally i just can found the different between digital and analog type, and some low cost circuits to build the hearing aids, but without equalizer.. so i am really not familiar with it and how was it work in the circuits.I know that it is use to boot and cut the frequency, but i not sure how to adjust it in the circuits . I am google about the 3-band tone controls but i found out that some people are calling it equalizer. I am searching for how they design the 3-band tone controls and how to calculate the value of cutoff frequency for each band, but i just can find the circuits without explaination of how they calculate and design the circuits.

The opamps in the tone controls circuit do not work properly when they are biased wrong. Maybe your simulation program does not know it.

I am connecting with the pre-amp to test the tone control now, but i am not sure that how was the waveform look like. May i know if i was connected pre-amp with tone controls, then the +ve of tone control no need to connect to 5v supply since the pre-amp there already have +5V? how about the parallel capacitor that previously connected in the +ve supply of tone control to blog the high and low freuqncy that cause by input source? should i disconnect them ? or i need to connect them in the +ve of pre-amp?

Thanks!

 

You have the pin 3 and pin 5 non-inverting inputs of the tone controls opamps wrongly connected to ground. They must be biased at half the supply voltage!
The preamp is biased correctly but it does not bias the tone controls opamps.

 

You have the pin 3 and pin 5 non-inverting inputs of the tone controls opamps wrongly connected to ground. They must be biased at half the supply voltage!
The preamp is biased correctly but it does not bias the tone controls opamps.

Now i reconnect the pin 3 and pin 5 with bias voltage, was it correct?

Thanks!

 

Your circuit is working properly now.

You don't need two sets of resistors. One set of resistors can bias thousands of Cmos opamps so connect pin 3 to pin 5 and use two resistors to bias them. Connect a 10uF capacitor to ground at the "half the supply voltage" point.

 

Your circuit is working properly now.

You don't need two sets of resistors. One set of resistors can bias thousands of Cmos opamps so connect pin 3 to pin 5 and use two resistors to bias them. Connect a 10uF capacitor to ground at the "half the supply voltage" point.

Thanks, now i would like to build a power-amp, may i know can i use the circuit below with a fix gain of 20 as my power-amp ?or i need to use an adjustable gain for hearing aid?

after the output of tone control (input of volume control), i am using a C with 0.16uF and a pontentiometer of 100k ohm as my capacitor and volume control.And after the volume control(input of power-amp), we need to put another coupling capacitor, may i know can i use the CR value with 1.5uF and 10k ohm resistor as my Coupling capacitor value?

Thanks!

 

Thanks, now i would like to build a power-amp, may i know can i use the circuit below with a fix gain of 20 as my power-amp ?or i need to use an adjustable gain for hearing aid?

All hearing aids have a volume contol but my hearing does not. Maybe the volume can be turned down when sounds are loud so the amplifier does not have severe clipping.

The LM386 power amplifier is cheap and is used in kids toys. It has hiss which is not good for a hearing aid. Its minimum supply is 4.0V or 5.0V. What will you use to power your hearing aid? Three button or AAA alkaline cells are 4.5V when brand new then drop to 3.0V. An LM386 might not work when the voltage is less than 4.0v or 5.0V. Find a newer amp that will work with a very low supply voltage.

after the output of tone control (input of volume control), i am using a C with 0.16uF and a pontentiometer of 100k ohm as my capacitor and volume control.And after the volume control(input of power-amp), we need to put another coupling capacitor, may i know can i use the CR value with 1.5uF and 10k ohm resistor as my Coupling capacitor value?

The input of the LM386 has a 50k resistor to ground. it is at 0V the same as the volume control so a coupling capacitor is not needed.