Dr.VPot
Member
hello colin, thanks for replying
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
AG,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??
ANY amplifier will clip if its input signal level is too much causes the output to try to go higher than is possible. An LM386 has a gain of 20 times but it can be 200 times if a capacitor is added between pin 1 and pin 8.
Your recordings had some very loud sounds like you were rubbing the mic in your hand or scraping the mic on the floor. When I hold my mic mounted in a lid on my chest then it does not move and does not produce those noises.
A piezo transducer picks up vibrations like from a guitar, piano or car engine. It makes a poor microphone.
If you look at the picture, my mic is not in contact with the chest piece, but as you said it pics up the rubbing on the diaphragm pretty louder. but why is it not picking up heartsounds? that's my question. both rubbing and heart sounds are produced from the same distance from the mic. it doesn't clip with rubbings or movement but its clipping the heartsounds when i put the chest piece on my chest. can you reason with that? do you think low frequencies are getting clipped?
Also can you show your chest piece in the jar lid? it would be of great help.