I'm building this noise generator to drown out my tinnitus but according to the scope waveform it appears to be picking up hum.

I know the TL082 doesn't have enough open loop gain at the middle of the audio bandwidth for a gain of 1001 but this is just a proof of concept circuit at the moment.

I assume, it's picking up hum because I built it on a breadboard and the long leads are picking up the mains. The interesting thing is it's only picking up the negative cycle at half the mains frequency. The power supply is my bipolar power supply which seems to be alright hum-wise.

Attached is the schematic and the waveform. The top waveform is the output from the noise generator and the bottom is the waveform generated when I hold the oscilloscope's probe and pick up hum.

I will build this on a propper PCB but before then, I want to ensure it works properly. Is there anything I might be doing wrong?

Attached Images

	Noise gen.gif (8.7 KB, 16 views)
	Noise gen and ripple.png (269.5 KB, 12 views)

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Your zener diode is connected upside down. So instead of zenering and making a lot of noise, it is just an ordinary forward biased diode but with a lot of current. So that explains why the gain of the opamp must be so high.

Also,get rid of the breadboard and make the circuit properly.

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Uncle $crooge

 

You're right, the zener is upside down but it's only a schematical error, the zener in the real circuit, is the right way up. I've edited the attachment.

I suppose I'll have to build it properly before I can get it to work well.

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hi hero,
I would be interested in how the tinnitus cancelling circuit works out.

I have tinnitus in both ears since the 1980's, when I damaged both of my ears working on a SMPS design.

The apparent frequency of my tinnitus is around 3 to 4kHz, low to medium loudness.

The specialists tell me there is nothing that can be done, except join a tinnitus group.

Regards

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Eric
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How did that happen?

Did a huge capacitor explode and take out your ear drums?

I got my tinnitus when I was about 15, I don't know, it just crept up on me. I had my hearing tested and they couldn't find any problems, except for a slight loss of sensitivity at the same frequency of the tinnitus, I was pressing the button saying I could hear the tone but it was jut the tinnitus, not the sound they were playing through the headphones.

It seems to be a problem with the nerves in my jaw, when I bite hard or push my jaw the tinnitus gets louder. I have a feeling that the nerves might have been damaged when I was involved in a fight and someone punched me in the jaw but I can't be certain.

The apparent frequency of my tinnitus is about 8kHz and varies quite widely in intensity, sometimes I can't sleep, but most of the time it isn't a problem.

The idea of this noise machine is to produce white noise to drown out the tinnitus, it sounds like a radio tuned out of station. I've tried leaving the radio on out of station before but it can suddenly randomly pick up a distant station which wakes me up. I've tried noise tapes but they have to be re-wound after so long.

I might add a low pass filter to output a pink noise as it's supposed to be less harsh sounding but at the moment I'll stick to white.

Currently I have this circuit set up in my bedroom with a piezo tranducer on the output, it produces enough noise to help me sleep and the piezo transducer doesn't have enough bass to reproduce the hum, so in a way it's fine as it is. When I finish the project, I'll add a speaker, an LM386 and split the amplification between two op-amps, I'll probably also add a pink noise filter which can be switched on and off.

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hi,
I was working in a confined space tuning a SMPS, [24Vdc to 5Vdc] trying to maximise the efficiency. I accidentally detuned it to within the human audio frequency band. I heard two or three very load 'cracks', at first I thought it was the SMPS, but the crack was in my ears.

I have had a 3 to 4kHz tone ever since, Ive tried a number of ideas but with no success.

Normally I have learned to live with it, but sometimes an external audio frequency will 'beat' with it and then its very unpleasant.

As you say sometimes the 'tone' completely disappears for a few minutes, especially during the night, at which time I can hear ever little noise clearly.

You can buy endless loop cassette tapes for your tape player.

It would be interesting to see what other members have tinnitus and if they have found a 'fix'

The 'Chit Chat' topics may be the place to ask.

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Eric
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Asprin and Tylenol pain drugs cause tinnitus in some people.
I am an old geezer (62) but I still hear pretty well. I can hear up to about 15kHz. I heard ultrasonic motion detectors clearly when I was young.

I think I have a little tinnitus because I hear low level very high frequency noise (12kHz to over 20kHz) all the time but it doesn't bother me.

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Uncle $crooge

 

I've nearly finished designing the circuit.

I'm going to connect a small speaker so I've decided to move most of the gain to the LM386 because the op-amps dont't have enough bandwidth over the audio range.

The diode produces about 250µV of noise which will be amplified by two op-amps, one with an optional filter selected by a switch to produce pink noise.

The circuit is pretty similar to the one below, except for the following:

• The op-amps have a much lower gain.
• They are both configured as single supply amiplifiers.
• I've put a DC bias on the capacitors so they don't need to be non-polarised.
• The noise source is a zener rather than a transistor.

Pink Noise Generator for Audio Testing

I have a question regarding the LM386 circuit: what value coupleing capacitor should I use?

The datasheet says 250µF but with an 8hm: speaker the lower cut-off frequency will be:



I've worked out that for 20Hz I need a 1000µF capacitor but is it really worth it as my cheap speaker will probably also roll-off at 80Hz.

Should I bother with 1000µF or go for 470µF which will give a roll-off of just over 40Hz and might be a good enough compromise?

Another question is, I'm tempted to go for a larger capacitor than 50µF for the ripple by pass capacitor; is it worth it? I'm going to use unregulated supply and ams worried that a 47µF capacitor at worst case might be only 37.6µF (-20% tolerance) so it might not be good enough. I'm tempted to go for 68µF or even 100µF.

To be honest, I've never used an LM386 before and I want reasonable performance but I don't want to use too oversized components.

Attached Images

Noise Gen1 - LM386.GIF (6.9 KB, 4 views)

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Use a high value output capacitor so the LM386 amplifier can damp the 100Hz to 200Hz boom sounds of the cheap speaker resonating.
You want wideband smooth noise, not a bongo drum.

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Uncle $crooge

 

I have your generic getting older tinnitus, I notice it in really quiet environments and have occasional loud ringing, somewhere around that 3-4k range. Getting more noticeble lately.
I did have an explosion incident when I was younger though =O. I unrolled and collected a dozen or so of those little novelty poppers (throw at the ground and they go off like caps) and wrapped them up in tissue to make a large one, loud as hell, it went so well I immediately and stupidly went to a dozen boxes of them. About six boxes in I noticed my face was getting warm and realized I was sitting in front of the heater vent in my room that had turned on. About 2 seconds later my mind went 'ding' (the stuff is thermally sensitive) and so did the bowl I was dumping the stuff into, more like a bang though. I had a mild powder burn to my face arms and neck (just a stinging sensation for a couple days) but I was stone cold deaf for a few hours and it took two weeks for the ringing to go away.
Live and learn I guess =) I think that was the first 'life' I lost =) I better keep count, I think I'm at least half way to 9 by now! I think 4 was nearly digging up the mains lines carrying 30-40KWs to the plant I work at (always ask your boss to see dig permits before your start working no matter how much you trust them!)

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