Dear All,
Let me introduce one of my project what I worked through 12 years back with a professor.
Still it need to be more efficient one.
Its a low cost hearing aid amplifier using LM324 as a main Op-amp.
We were trying to apply 3 frequency selecting gain circuits, 1. Bass Control 2. Mid frequency 3. Treble control.
I did apply some model from online for having suitable gain at human sensor range like 2-3KHz.
It looks clear, I have been trying
1. Treble and Bass control by frequency selecting gain, considering High, low and mid frequency gain through frequency selector.
2. Tried to boost and buck the gain of the amplifier.
3. Assume all OPAMPS are 741.
4. In mid frequency band the gain should be 17dB to -15dB. According to this design, as audio signal is fed by single input, so all frequency signal from the air will be chosen by selector, must be flat for minimum frequency gain.
5. As far as I remember, 200Hz to 8kHz, we have used signal generator.
6. My tone controls have parts to boost the frequencies and other parts to cut the frequencies. Are there any people with hearing problems that need frequencies cut because their hearing is "too sensitive" to those frequencies?
Take a look in the bode plot here,
Not sure the system works properly.
Suggest for meaningful simulation.
Let me introduce one of my project what I worked through 12 years back with a professor.
Still it need to be more efficient one.
Its a low cost hearing aid amplifier using LM324 as a main Op-amp.
We were trying to apply 3 frequency selecting gain circuits, 1. Bass Control 2. Mid frequency 3. Treble control.
I did apply some model from online for having suitable gain at human sensor range like 2-3KHz.
It looks clear, I have been trying
1. Treble and Bass control by frequency selecting gain, considering High, low and mid frequency gain through frequency selector.
2. Tried to boost and buck the gain of the amplifier.
3. Assume all OPAMPS are 741.
4. In mid frequency band the gain should be 17dB to -15dB. According to this design, as audio signal is fed by single input, so all frequency signal from the air will be chosen by selector, must be flat for minimum frequency gain.
5. As far as I remember, 200Hz to 8kHz, we have used signal generator.
6. My tone controls have parts to boost the frequencies and other parts to cut the frequencies. Are there any people with hearing problems that need frequencies cut because their hearing is "too sensitive" to those frequencies?
Take a look in the bode plot here,
Not sure the system works properly.
Suggest for meaningful simulation.
Is R12 supposed to be only 47 ohms? That means U6 and U7 are fighting each other through a low impedance path.
The LM324 has no mention of noise levels at all in one datasheet, and 40nV in another - sure that's a good choice? Why is the first stage a follower - that's not going to do anything for the noise performance? I'd expect some non-inverting gain in the first stage to boost levels above the noise-floor for the rest of the circuit.
The LM324 has no mention of noise levels at all in one datasheet, and 40nV in another - sure that's a good choice? Why is the first stage a follower - that's not going to do anything for the noise performance? I'd expect some non-inverting gain in the first stage to boost levels above the noise-floor for the rest of the circuit.
Besides noise canceling, U1 may be use for impedance matching. Middle part of the circuit is wein bridge type oscillator. Do you want me to R12 as 47k?
It looks like you're trying to emulate conventional tone control circuits for a hearing aid. I think your circuit is cumbersome, redundant, and marginally effective for the application.
How about having several response profiles that are switched by microprocessor or TTL circuitry? Determine appropriate profiles empirically, with actual hearing impaired test subjects. You could use only one op amp for this instead of 5 (5!).
No I'm not going to design it for you. You're the student.
How about having several response profiles that are switched by microprocessor or TTL circuitry? Determine appropriate profiles empirically, with actual hearing impaired test subjects. You could use only one op amp for this instead of 5 (5!).
No I'm not going to design it for you. You're the student.
An oscillator is definitely not wanted! I would expect some sort of Baxandall tone control circuit here, there are many variations.
Have you looked at shape and depth of typical hearing losses?
Survey:
Me and my dad:
Note that Dad had a 45dB/Oct slope from 1kHz to 2kHz... no simple filter can boost that. (Or even half of that, since an old-old starting guide is to correct half the loss.)
And the electronic issues the others will point out. All your gain is at the end. You have loss where none is needed. Inappropriate values. Inconsistent drawing.
There's enough confusion and wrong-thinking in the hearing aid field. Don't add to it.
Survey:
Me and my dad:
Note that Dad had a 45dB/Oct slope from 1kHz to 2kHz... no simple filter can boost that. (Or even half of that, since an old-old starting guide is to correct half the loss.)
And the electronic issues the others will point out. All your gain is at the end. You have loss where none is needed. Inappropriate values. Inconsistent drawing.
There's enough confusion and wrong-thinking in the hearing aid field. Don't add to it.
You're doing his homework for him! Good info though; very useful.
It seems to me that his instructor gave him an assignment without any direction. If someone is really interested in working in the hearing aid industry, then they should take some speech and hearing science classes.
It seems to me that his instructor gave him an assignment without any direction. If someone is really interested in working in the hearing aid industry, then they should take some speech and hearing science classes.