audioguru2
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I am anxious to see your "noise generator circuit".
No negative feedback like the original circuit has in a couple of places?
No negative feedback like the original circuit has in a couple of places?
this is the preamplifier I used-----R1 R3 R4=10K----R2+1K--R5=100K to 1M-----C1=0.1uf ---C24.7uf
View attachment 36014
View attachment 36014
audioguru2
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Hi Doctor Emad,
Why did you change so many parts of the preamp? Now it is nothing but a mid and high audio frequencies noise generator, as you reported.
1) The KIA358 (LM358 sub) opamp has a high noise level and crossover distortion. A low-noise opamp was recommended.
2) Its gain is too high so it will amplify its own high noise level and background sound too much.
3) Like the original circuit, the value of its C1 is much too low so it will attenuate low-frequency heartbeat sounds too much.
4) Its R1 and pin 3 are not decoupled from the supply so it may "motorboat", especially when the battery gets low.
5) C2 blocks the DC voltage reference that is required for the following U2 stage.
6) You probably didn't use the U2 filter circuit, whose function is to reduce noise and background sound.
Why did you do this?
Why did you change so many parts of the preamp? Now it is nothing but a mid and high audio frequencies noise generator, as you reported.
1) The KIA358 (LM358 sub) opamp has a high noise level and crossover distortion. A low-noise opamp was recommended.
2) Its gain is too high so it will amplify its own high noise level and background sound too much.
3) Like the original circuit, the value of its C1 is much too low so it will attenuate low-frequency heartbeat sounds too much.
4) Its R1 and pin 3 are not decoupled from the supply so it may "motorboat", especially when the battery gets low.
5) C2 blocks the DC voltage reference that is required for the following U2 stage.
6) You probably didn't use the U2 filter circuit, whose function is to reduce noise and background sound.
Why did you do this?
audioguru2
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Hi again Doctor Emad,
If you want to try my corrected circuit using a dual opamp, the pins on the opamps package can be connected like this:
View attachment 36021
If you want to try my corrected circuit using a dual opamp, the pins on the opamps package can be connected like this:
View attachment 36021
Hi Audaguru. I sent for the TL072 but I dont know it will be present or not. I told u before that I connected the output of the LM358 to the input of the LM386 using just two ICs and I have a satesfactory result. I removed some noise by adding 0.1uf between the variable R of U2 and the negative volt. I ask if I can put anoise removing circuit between the two ICS????? If I can, what is the suggested circuit????? THANX
audioguru2
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Hi Doctor Emad,
A TL072 or a KIA358 has two opamps inside. Your preamp circuit used only one of them. My latest schematic shows how to connect its pins for use as U1 and U2.
Before you said that your circuit just made a noise sound like shshshshshshsh. Now you say it was a satisfactory result. ???
Now you want to remove that noise. The value of your C1 was much too low so you used more gain which increased the noise. ???
The function of U2 (that you didn't use) is to remove noise!
While waiting for the TL072 low noise dual opamp to arrive, why not use an 8-pin IC socket for a dual opamp like my latest schematic and try the circuit with your KIA358? Then simply unplug the KIA358 and plugin the TL072 later.
A TL072 or a KIA358 has two opamps inside. Your preamp circuit used only one of them. My latest schematic shows how to connect its pins for use as U1 and U2.
Before you said that your circuit just made a noise sound like shshshshshshsh. Now you say it was a satisfactory result. ???
Now you want to remove that noise. The value of your C1 was much too low so you used more gain which increased the noise. ???
The function of U2 (that you didn't use) is to remove noise!
While waiting for the TL072 low noise dual opamp to arrive, why not use an 8-pin IC socket for a dual opamp like my latest schematic and try the circuit with your KIA358? Then simply unplug the KIA358 and plugin the TL072 later.
audioguru2
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Hi Trigger,
The power source (battery) doesn't produce any noise. The noise comes from inside a noisy opamp, U1, and is amplified by its high gain.
If you divide R1 (10K) into two 5K resistors with their junction decoupled to ground, you will decrease the output of the microphone, because its high output impedance (current source) FET also needs a high impedance load (but too high will create resistor thermal noise).
You quoted Doctor Emad's own mic preamp circuit, with its very low value of R2 (to get more gain from U1) which loads-down the mic's output even more. Are you also going to use his very low value for C1 which attenuates the low frequency heartbeat signal? And the adjustable gain for R5 which makes the gain up to 21 times too high?
For me, it sounds like you are also building a noise generator like Doctor Emad did.
The power source (battery) doesn't produce any noise. The noise comes from inside a noisy opamp, U1, and is amplified by its high gain.
If you divide R1 (10K) into two 5K resistors with their junction decoupled to ground, you will decrease the output of the microphone, because its high output impedance (current source) FET also needs a high impedance load (but too high will create resistor thermal noise).
You quoted Doctor Emad's own mic preamp circuit, with its very low value of R2 (to get more gain from U1) which loads-down the mic's output even more. Are you also going to use his very low value for C1 which attenuates the low frequency heartbeat signal? And the adjustable gain for R5 which makes the gain up to 21 times too high?
For me, it sounds like you are also building a noise generator like Doctor Emad did.
audioguru,
Noope I am not going to build this circuit. Just quote a pass experience in handling condensed microphone circuit in manufacturing products (say for example, an microphone preamp stage inside an analog cmos camera connected to your VCR/TV).
The suggestion is to minimize the noise/ripples come from the path of the supply, which is generated by other parts of the circuit.
You may noticed "humming" sound at the later amplify stage if that modification hasn't included.
Remember, you got to eliminate the possible noise before tha amplify stage else no matter what opamp you are using, you are going to amplify both the required signal and noise..... and gradually make the circuit fails.
Noope I am not going to build this circuit. Just quote a pass experience in handling condensed microphone circuit in manufacturing products (say for example, an microphone preamp stage inside an analog cmos camera connected to your VCR/TV).
The suggestion is to minimize the noise/ripples come from the path of the supply, which is generated by other parts of the circuit.
You may noticed "humming" sound at the later amplify stage if that modification hasn't included.
Remember, you got to eliminate the possible noise before tha amplify stage else no matter what opamp you are using, you are going to amplify both the required signal and noise..... and gradually make the circuit fails.
audioguru2
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Hi Doctor Emad,
You are correct.
You don't need U4. It just flickers the LED during each heartbeat which looks nice. U4 and the LED also waste battery power.
You are correct.
You don't need U4. It just flickers the LED during each heartbeat which looks nice. U4 and the LED also waste battery power.
hi Audioguru. I consrtucted the circuit with the TLO72 on a test board but there is just noise and nothing from the mic goes to the earphones. What is your opanion about this circuit in the site I put here
, and can I use TLO72 insteed of NE5532 ?????
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audioguru2
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Hi Doctor Emad,
Which circuit did you constuct? (We have many, now). I don't know why it doesn't work, when it worked before but was noisy. It should work fine and with less noise with the TL072.
The "auto" stethoscope that you posted is very similar to our corrected one, but uses a 3-wire electret mic and has much more gain (and therefore more noise). Its simple "tone control" noise filter is not nearly as good as our corrected U2 precision filter.
The NE5532 has lower noise than a TL072 but still has noise. I have used both for mic preamps and they sound the same (perfect).
Since the "auto" stethoscope circuit doesn't use a power amp, it must be used with high-impedance headphones.
Now that you have constructed our corrected circuit (I hope that you built that one), don't you want to troubleshoot it? There is probably something very simple that is wrong.
If you speak into the microphone, about 20cm away, do you hear your voice clearly in your earphones? The U2 filter will reduce high frequencies but your voice should still be heard.
When you turn its volume control down, does the noise reduce to nearly nothing?
What does the noise sound like?
Which circuit did you constuct? (We have many, now). I don't know why it doesn't work, when it worked before but was noisy. It should work fine and with less noise with the TL072.
The "auto" stethoscope that you posted is very similar to our corrected one, but uses a 3-wire electret mic and has much more gain (and therefore more noise). Its simple "tone control" noise filter is not nearly as good as our corrected U2 precision filter.
The NE5532 has lower noise than a TL072 but still has noise. I have used both for mic preamps and they sound the same (perfect).
Since the "auto" stethoscope circuit doesn't use a power amp, it must be used with high-impedance headphones.
Now that you have constructed our corrected circuit (I hope that you built that one), don't you want to troubleshoot it? There is probably something very simple that is wrong.
If you speak into the microphone, about 20cm away, do you hear your voice clearly in your earphones? The U2 filter will reduce high frequencies but your voice should still be heard.
When you turn its volume control down, does the noise reduce to nearly nothing?
What does the noise sound like?
Hi Adioguru. I constructed your corrected circuit. It is more than excellant .No distortion , minimal noise and the sound is the same like a real stethoscpe. I can hear my heart beats and respiratory sounds laod and clear from above clothes . I dont know how can I thank you fore helping me . thaaaaaaaaaaaaaaaaaaaaank youuuuuuuuuuuuuuuuuuuuuuuuuuu
audioguru2
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Hi Doctor Emad,
I am happy to hear that you got your corrected project working properly and am glad to have helped you.
Thank-you for helping me prove that my ideas, corrections and simplifications work very well.
I will post my corrected circuit as a new project. ;D ;D ;D 8)
I am happy to hear that you got your corrected project working properly and am glad to have helped you.
Thank-you for helping me prove that my ideas, corrections and simplifications work very well.
I will post my corrected circuit as a new project. ;D ;D ;D 8)
audioguru2
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Hi Doctor Emad,
You don't need the blinking LED. Without U4, the new (TL072) corrected circuit has only two ICs and is very small.
You don't need the blinking LED. Without U4, the new (TL072) corrected circuit has only two ICs and is very small.
Hi Audioguru
Congratulations! You have made a good stuff again!
By the way, I undersdtand that we have a university here conducting an R&D project on electronic stethoscope. It is said that the new device have many good features and would evetually replace the traditional mechanical ones ....
This is an intersting as well as useful project !
Oli
Congratulations! You have made a good stuff again!
By the way, I undersdtand that we have a university here conducting an R&D project on electronic stethoscope. It is said that the new device have many good features and would evetually replace the traditional mechanical ones ....
This is an intersting as well as useful project !
Oli
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