I see. but my microphone has 10v as max rating, having a 15v would be a problem right? but i can try with +9v and -9v. so you think that distortion is due to opamp saturation? not related to mic itself?The datasheet says the op-amp can handle a power supply of up to 30V across across it's power pins. So you can change 9V to 30V, or you can change both AGND and 9V to -15V and +15V, respectively.
That will allow the op-amp to produce a higher voltage to correspond to the higher output volume without saturating.
Then power your microphone off 10V and power the amplifier off 30V. Just make sure they share a common. Separate the voltage supplies between the amplifier and the microphone. Probably disconnect the top of R1 and C3 from everything so you can connect it to another power supply.I see. but my microphone has 10v as max rating, having a 15v would be a problem right? but i can try with +9v and -9v. so you think that distortion is due to opamp saturation? not related to mic itself?
I would definitely try that, thanks. Were you able to hear the sound clip and you think its saturation?Th
Then power your microphone off 10V and power the amplifier off 30V. Just make sure they share a common. Separate the voltage supplies between the amplifier and the microphone. Probably disconnect the top of R2 from everything so you can connect it to another power supply.
This op-amp doesn't have a common connection for a bipolar supply so it might be easier to just go 0V and 30V so that it can share the ground with the microphone. Or else you will have to use a couple of capacitors to produce an artificial common for the microphone if you use a bipolar supply on the op-amp.
I would definitely try that, thanks. Were you able to hear the sound clip and you think its saturation?
there is a famous circuit by audioguru https://www.aaroncake.net/circuits/steth.asp , they used tl072 with +9v and -9v (it also has low pass filter). do you think that's better or would you recommend any other opamp or a different electret condenser mic instead, that serves my purpose best? also what's your take on MEMS mic? i was thinking of implementing this https://www.instructables.com/id/Electronic-Stethoscope-With-MEMS-Microphone-and-Re/
I apologize for lot of questions. take your time
The mic circuit I posted at Aaron Cake's site uses a dual opamp. One opamp is the preamp and the second opamp is a lowpass filter. The "stethoscope head" shields the mic from background sounds.
Your recording sounds like the first speech has the opamp clipping like crazy, increasing the supply voltage will make only a small improvement. Turn down the gain when the sounds at the mic are loud.
If you need high gain for weak sound levels then you need an automatic volume control (AVC) like is used in a sinewave generator circuit that uses a Jfet to adjust the gain. Adafruit has a mic with preamp and auto-gain control.
Hello audio guru, i appreciate your reply.The mic circuit I posted at Aaron Cake's site uses a dual opamp. One opamp is the preamp and the second opamp is a lowpass filter. The "stethoscope head" shields the mic from background sounds.
Your recording sounds like the first speech has the opamp clipping like crazy, increasing the supply voltage will make only a small improvement. Turn down the gain when the sounds at the mic are loud.
If you need high gain for weak sound levels then you need an automatic volume control (AVC) like is used in a sinewave generator circuit that uses a Jfet to adjust the gain. Adafruit has a mic with preamp and auto-gain control.
EDIT: The circuit might be clipping on loud sounds because it is overloaded. An opamp cannot properly drive a speaker or headphones, a power amplifier must be used like the LM386 in my mic stethoscope project at Aaron Cake's site.
The mic circuit I posted at Aaron Cake's site uses a dual opamp. One opamp is the preamp and the second opamp is a lowpass filter. The "stethoscope head" shields the mic from background sounds.
Your recording sounds like the first speech has the opamp clipping like crazy, increasing the supply voltage will make only a small improvement. Turn down the gain when the sounds at the mic are loud.
If you need high gain for weak sound levels then you need an automatic volume control (AVC) like is used in a sinewave generator circuit that uses a Jfet to adjust the gain. Adafruit has a mic with preamp and auto-gain control.
EDIT: The circuit might be clipping on loud sounds because it is overloaded. An opamp cannot properly drive a speaker or headphones, a power amplifier must be used like the LM386 in my mic stethoscope project at Aaron Cake's site.
Hello audio guru, i appreciate your reply.
I understand your explanation but my only surprise is why a chestpiece diaphragm movement is causing so much loud spl to clip opamp? isn't it very feeble?
Also my goal is to amplify heartsounds significantly loud and i'll be using only earphones. so will your popular circuit can serve my purpose? yes i would be interested in AVC, but are there any chips or circuits i could use for my prototyping? thanks in advance
hey AG,Most opamps are spec'd driving a load no less than 2000 ohms. What is the impedance of your headphones? 32 ohms for each ear then in mono (both ears in parallel) the load is 16 ohms which is much too low for an opamp to drive.
This 2.2K over here, or that one over there?2k2 is far too low for 9v supply.
hello colin, thanks for replying2k2 is far too low for 9v supply. It should be 22k to 47k. I make electronic stethoscopes for safe cracking and you can also use a piezo diaphragm
Hello AG,Your distorted recording has the amplifier clipping like crazy. All amplifiers clip when they are trying to produce more output level than is possible. You need an auto level control or compressor circuit but some circuits react too slowly then the distortion comes before they cut the level down. Maybe you have the mic touching and moving on the chest.
When I tested my electronic stethoscope I mounted the mic on a peanut butter jar plastic lid then the lid touched the chest and blocked background noise and the mic was not touching the chest. I was able to use an LM386 power amplifier and loudspeaker without having any acoustical feedback howling. My heart sounds were loud and the amplifier was not clipping.
Bose provides no spec's on their expensive headphones like frequency response, maximum power and impedance. They just say important things like the PRICE, color and weight.
The TL071 circuit has a 100k gain control labeled VOL. With the 100k trimpot set to 100k then the gain is 1+ (100k/2.2k)= 46.5 times which is good when you talk in a normal conversation level about 5cm away from the mic. With the trimpot set at half rotation then the gain is 23.7 times and you would need to talk a little louder or hold the mic closer to your mouth. With the trimpot turned down all the way then the gain is only 1 and if you scream very close to the mic then you might not be heard. Then why change the 2.2k to 22k??were you talking about the 2.2k in the tl071 circuit? if i increase the resistor value from 2.2k to 22k the gain drops drastically right? correct me if i'm wrong
when you said piezo diaphram, were you talking about piezo based microphone or sensor?
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