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TL071 Audio Amplifier with 6 channel mixer.

gary350

Well-Known Member
I used online filter calculator to find the value of each Hz filter for 6 channel mixer to match my hearing test to build a hearing aid. Each filter needs a volume continue but I have no clue where 6 volume controls should be without screwing up each filter?

 

ronsimpson

Well-Known Member
Most Helpful Member
You have 6 filters in parallel. What you actually built; is all 6 caps in parallel that works like one large cap. AND The 6 resistors are also in parallel making one very low value resistor.

Sesrch for "schematic audio equalizer".
 
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gary350

Well-Known Member
I did Google search for, audio equalizer circuits, there are lots of incomplete circuits, many have 6 paralle circuits like mine but the circuit has 6 seperate outputs or 6 seperate inputs. I don't know the correct way to build an audio equalizer I need a complete circuit..
 
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ronsimpson

Well-Known Member
Most Helpful Member
Are you wanting a circuit where there are 6 controls? Example; 3 controls equals "Base. Mid, Treble ".
 

gary350

Well-Known Member
If I had parts values I could build this. IC numbers is a TL071. R7 is 220 ohms. ???

 
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gophert

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Most Helpful Member
gary350
Thank you for being part of ETO, your posts are very entertaining and your frantic pace of interest changes reminds me of a goldfish discovering a new thing with each trip around the fishbowl. I think you have started nearly half of the new threads lately. This place would be significantly more boring without you.
 

gary350

Well-Known Member
Will this circuit work. A speaker on each filter. Not what I really want I would like all the sound coming out of an ear phone. A few years ago I had a pocket size audio equalizer the size of my cell phone I wish I still had it. 6 speakers in the same speaker box will sound like 1 speaker. Still no volume control on each speaker. Probably need an LM386 for all those 2" speakers.
 
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AnalogKid

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Most Helpful Member
Since I don't track every thread, please explain what it is you are trying to achieve. What I see is a microphone and preamp, followed by a six-band equalizer, followed by a speaker out. If that is the goal, then the preamp is ok, the equalizer sections are highpass only, and you need a separate speaker amplifier with a summer at the input. Do you want to both boost and cut the frequencies in each filter band?

Separate from that, you should adjust your expectations. Filters are not "brick wall" circuits. The response of each section affects the signal frequencies intended for other sections. This is particularly true when the center frequencies of the filter sections are close together. For example, the 1447 Hz circuit, whatever it is, will affect both 1061 Hz and 1990 Hz frequency bands.

To reduce this crossover, most audio equalizers use active filters, not simple R-C sections. Here is a schematic that will give you an idea of the circuit complexity needed. Each section is a tuned resonant circuit based on a gyrator - an opamp circuit that is a synthetic inductor. There are other ways to go that use fewer parts, like ones based on the tone control circuits in a stereo but with more sections than just bass and treble, but those circuits do not have the selectivity of ones similar to this.

ak

 

gary350

Well-Known Member
I went to the hearing aid doctor yesterday to get an adjustment. It has taken 2 years to finally get them close to working the correct way. It is very hard to go there get an adjustment in the quiet office then go out into the real world and expect the volume level to be correct. Both hearing aids have 3 settings from the click of a button, 1, 2, 3. 1 is low volume, 2 is medium volume, 3 is higher volume to be used when needed. Driving in car sounds like being in a tornado so I use volume 1 to lower sound. Volume 3 is good to hear the birds, and natural sounds outside even helps sometimes to hear the TV. Yesterday I went to the hearing aid doctor, I told him #2 volume on RIGHT hearing aid is perfect do not change it, lower #1 volume a little bit. Also told him volume 1 on left hearing aid is perfect do not change it, Swap 1 with 2. The doctor claimed he understood. He said it will take me a few minutes to make the change. To make long store shorter doctor deleted both hearing aid programs and started over, new program is all screwed up. I told doctor that is terrible change it back the way it was. He said, I can't old programs were deleted. I said, I told you not to change volume #2 it is perfect on right ear, not change volume 1 on left ear. He said, I thought this is what you wanted. We worked 30 minutes in his office trying to get a good setting again but nice quiet office is not the real world I have no clue how well it works until I leave, drive car, go home, talk to wife, listen to TV, hear every day sounds, etc. Hearing aids are so screwed up so bad I can not wear them. Now I need to return try to get them adjusted again. Makes me so MAD I could scream nothing is saved in memory every visit is trial and error. Trial and error at the doctor is a pain in the ass I need my own volume control adjustment. My 3 years of free office visits expire in July. I have learned NEVER buy hearing aids that can only be adjusted at the hearing aid office it never works once your out in the real world. The assistant does a better job of getting settings correct than the doctor.

I am so frustrated I am ready to build my own hearing aid again. I built hearing aids several years ago it was just a little op amp with ear phones with my own volume control is works better than factory hearing aids because I can change volume when needed but it would be BETTER if op amp has a filter circuit to DOUBLE volume at 1500 to 2000 Hz range and TRIPLE volume at 3000 Hz range and up.

See old and new volume settings. See attachment of hearing test.



 
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audioguru

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Most Helpful Member
You have the results of your hearing test that shows that the high frequency boost is needed only above 1kHz so why does your circuit have six frequencies?

Your filters have six 10 ohm resistors in parallel with an earphone or a pair of earphones. Then if the earphones are high impedance 600 ohms, the load on the TL071 opamp is 1.7 ohms. But the datasheet for the opamp shows a minimum allowed load of 2000 ohms.

Your filters will do nothing because they are all in parallel. If the resistor and capacitor values of one filter are 200 times or more higher and it has a high impedance load like the input of a power amplifier then it would cut low frequencies only gradually because the filter is not active (it is passive) and it has only one capacitor and one resistor (1st order).

Your hearing test shows a high frequencies dropoff at 45dB/octave. One RC drops off at only 6dB/octave. Then your highpass filter (or high boost circuit) needs 45/6= 7.5 identical RC circuits inside the negative feedback loop of an opamp. A complex 7th order highpass filter.

My hearing high frequency loss is about one-fifth of yours and my hearing aids boost the highs exactly to what is needed. I have a setting which has automatic noise reduction and compression. The noise reduction works well and the compressor reduces the levels of very loud sounds. Then they do not need a volume control but I asked for two volume settings. One setting is MUTE and the other setting increases the sensitivity a lot so that I can hear very low sound levels and for snooping on people talking far away. The hearing aids are also directional, picking up the loudest speech from one direction but rejecting people talking and noise at all other directions. I asked for a music setting with all the tricks turned off.

One of your ears hears nothing and the other does not hear anything above 2kHz so a hearing aid needs a miracle to give you hearing. My digital hearing aids have a program option that takes high frequencies from 4kHz to 20kHz and converts them down to 1khz to 4kHz. The audiologist did that on my hearing aids and asked me how I liked it. It sounded AWFUL and I asked for it to be turned off but you might like it for your best ear.

Many deaf people have a "cochlear transplant" where an electronic device picks up sounds and feeds the response to your hearing nerve.

Here is a graph showing one RC 1st order highpass filter up to a 7th order and how much boost at high frequencies you need. I show the schematic of a 3rd order Sallen-Key active highpass filter.
 

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audioguru

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Most Helpful Member
The tone controls circuits you found have a very gradual amount of boost as a 1st order passive filter. The equalizer circuits boost with about a 2nd or 3rd order filter. You need a 7.5th order filter. You need a lot of boost beginning at ONE frequency, 1kHz.

What happened to your hearing? Did you play with guns?
 

gary350

Well-Known Member
The tone controls circuits you found have a very gradual amount of boost as a 1st order passive filter. The equalizer circuits boost with about a 2nd or 3rd order filter. You need a 7.5th order filter. You need a lot of boost beginning at ONE frequency, 1kHz. What happened to your hearing? Did you play with guns?
A few years ago I could not get hearing aids that worked for me. New technology has made louder hearing aids. Hearing aid works very good on my right ear. My left hearing aid has twice the volume as the right hearing aid it is almost as loud as it needs to be. With both hearing aids I hear good. They were working about 95% yesterday until the idiot doctor deleted both programs. Today they are both screwed up so bad I can not hear with them at all , sounds like electric clothes dryer tumbling 50 empty glass bottles. I have another hearing aid adjustment today at 3:30 pm I hope it is with the assistant he is much better getting them adjusted than the doctor.
 
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audioguru

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I recently received an email from my hearing aids store saying that my hearing aids are more than 3 years old then I am eligible for another government grant for replacements and the store will give me another 30% discount. They will give me another free hearing test and show me and demo new hearing aids. They are hungry for my money. My existing hearing aids are perfect, how can new ones be better? I will go to see.

My new Google Assistant is pretty darn smart and answers immediately. Maybe new hearing aids do language translations and lookup stuff on the internet.
 

gary350

Well-Known Member
audioburu, when you explain things it helps me to learn, I am starting to understand but still have a long way to go. I was originally thinking each filter needs a volume control but now I think each filter needs it own op amp. Can the inputs of several amps be connected the the same mic and powered by the same battery? Many of the filter circuit I found have the filters on the input of the amps but that seems like the filters are all still connected in parallel. I can not find a series RC filter calculator online only thing available are T and pi filters calculators. Volume control still have to be on the input of all op amps. With filter resistor = 2000 ohms capacitor = .0265uf for 3000 Hz. Looks like several caps in parallel are needed to get .0265uf? I was hoping for a simple circuit, 3 to 6 filters and 1 amp?

Looking at my hearing test looks like I need 6 filters, 250, 500, 1000, 1500, 2000, 3000 and up for right ear. 250, 500, 1000 to 1500, 2000, 3000 and up for left ear. T type filter resistors have to be 2000 ohms or higher for output if TL071. Datasheet says input resistance of TL071 is 10 to 12 power 10,000,000,000,000. ohms. Circuit filters are all series RC for the ones I see online. It would be easier for me to copy the circuit above & change the values of the filters to get the HZ I need and us TL071 instead of the 2 transistors.
 

ronsimpson

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Most Helpful Member
We all know how "base & treble" work. We have talked about having a knob for each octave. There is another option. Can,t rember the name. For Base you have two controles. One for gain and one for frequency. You can set the low end gain for + or - 10db then set where you want that to start.
Same thing on the high end. Set the gain and set to 1khz or 2k or 3k ...
 

audioguru

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Most Helpful Member
Gary, you need only one highpass filter that boosts beginning at 1kHz and at 45dB/octave. Your hearing test clearly shows that for your "good" ear.
As I showed, you need a 7th order highpass filter. I showed the schematic a 3rd order highpass filter.

The tone controls and equalizer circuits that you do not need have no gain so a mic preamp circuit is needed to feed them. The tone controls and equalizer circuits are for people with normal hearing to make small corrections on the sounds from cheap speakers. Your severe high frequency hearing loss in your "good" ear needs one extremely high correction beginning at 1kHz for 45dB/octave.

You posted a horrible equalizer circuit from eleccircuit.com (in India?) that I think does not work.

Here is your hearing graph and what is needed to fix only a little bit of it:
 

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