• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

TL071 Audio Amplifier with 6 channel mixer.

audioguru

Well-Known Member
Most Helpful Member
I was correct, the equalizer circuit is completely wrong. I simulated it and found that the transistors are biased wrong and the circuit has almost no output level even though I have the tone control for the lowest frequency at maximum.

The transistor amplifier was non-inverting like an oscillator instead of inverting and I fixed the biasing.
 

Attachments

gary350

Well-Known Member
I was correct, the equalizer circuit is completely wrong. I simulated it and found that the transistors are biased wrong and the circuit has almost no output level even though I have the tone control for the lowest frequency at maximum.

The transistor amplifier was non-inverting like an oscillator instead of inverting and I fixed the biasing.
Can I use an Electret Mic on that?
 

JonSea

Well-Known Member
Most Helpful Member
Gary seems to have a unique ability to inconvenient information. Audioguru has said a number of times that Gary needs a 7th order highpass filter, at a fixed cutoff frequency. The equalizer circuit, with several filters at 6dB/octave, is not going to help Gary's hearing at all.

One complex filter, commonly called a brick wall filter, is what's needed. This isn't going to be accomplished with a few resistors and capacitors salvaged from TV sets.
 

gary350

Well-Known Member
It is amazing I can watch TV with ear phones plugged into the TV and I hear every sound, I hear sounds I have not heard in 40 years. Without ear phones sound that travels through the air to me lots of frequencies are missing it is very hard to understand what people say. The LM386 amp I built works good with earphones I use it outside to hear wind blow through the trees and birds in the trees. I turn the volume up until I hear what I want to hear. It works good as long as it is quiet outside with no other sounds for the amp to amplify. I have been thinking if I could bring all the different frequencies closer to the correct volume of my ear the amp and earphones will work better.
 

audioguru

Well-Known Member
Most Helpful Member
Can I use an Electret Mic on that?
The equalizer circuit (from a hobbiest website in India?) is shown on my simulation not to work because it has many things wrong.
An electret mic must be powered and must have a preamp with a gain of 100 to 300 times to feed a properly designed equalizer circuit.
But you do not need the equalizer circuit so forget about it.

It is amazing I can watch TV with ear phones plugged into the TV and I hear every sound, I hear sounds I have not heard in 40 years.
The LM386 amp I built works good with earphones I use it outside to hear wind blow through the trees and birds in the trees. I turn the volume up until I hear what I want to hear. It works good ….
It is amazing that your deafness can hear anything above 1kHz without having a lot of boost. Most young people can clearly hear up to 20kHz.
Your deafness is so bad that boosting above 2kHz will take a lot pf power that will destroy the remains of your hearing and destroy he earphones.

I have normal-for-my-age (73) high frequency hearing loss. It is -10dB at 125Hz then drops to -70dB at 8kHz. Then the boost needed is 12dB/octave which works well with the custom earmolds with the tiny speakers in them, they fit in my ear canals (the small hearing aids sit on top of my ears). Your hearing loss is almost 4 times as bad as mine.
 

Tesla23

Member
Your hearing loss reminds me of my late father's, almost completely deaf in one ear and a rapid rolloff above 1kHz in the other.

About 20 years ago he presented me with a graph like yours and his initial request was to help him hear the TV, without deafening everyone else. I made him an adjustable box that let him vary the high-pass (boost) frequency and rate of boost (2nd, 3rd or 4th order), followed by a tunable 6th order low-pass filter. I did this using switched capacitor filters, a single MF10 for the high-pass and a MF6 for the low pass, coupled with a couple of CD4046 chips that I had on hand as adjustable VCOs - allowing simple tuning of the filter cutoff frequencies.

Although the box allowed him 4th order boost (and even that was not near enough to compensate for his ear's rolloff), he settled on using the 3rd order. It gave him nearly 10dB boost in the mid frequencies without touching the lower ones. He loved it. I never looked at trying to improve his hearing aids, but he was never really happy with those. I don't know what he would have made of the newer devices.

Interestingly, I get annoyed with pop songs as I often cannot follow the words, but if I used his box they would often come out clear as day.

The MF10 seems to be still available, but not the MF6 as far as I can see. There are other switched capacitor filter ICs available though. I can't find the schematics, but I do have a calculated filter response that illustrates the sort of response I was aiming for:

1547859236480.png
 

Latest threads

EE World Online Articles

Loading

 
Top