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  1. audioguru2

    Electronic Stethoscope

    The electret material has long molecules that are made as a metalized diaphragm, back-plate or front-plate of the electret microphone. The electret material is heated and 50V is applied to it. When it cools, the 50V charge remains on it . Manufacturers say the charge lasts 10 to 25 years. 
  2. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Hi Roderick, Your inverter is smaller than it looks in your pics. ;D
  3. audioguru2

    9V battery & cap

    Sure the battery makes a lot of noise. It is screaming, "low-batt, low-batt, low-batt, low-batt" as loudly as it can. ;D [move] ;D ;D ;D ;D ::)
  4. audioguru2

    Electronic Stethoscope

    Hi Alun, What isn't true? Many articles in Google say that a voltage charge is placed in an electret material in the diaphragm, back plate or front plate. You can't measure the voltage charge because your meter will drain it away. I have also looked inside them and used the tiny FET transistor...
  5. audioguru2

    Electronic Stethoscope

  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Sasa, Welcome to our forum. ;D It sounds like your pot P1 is broken. Its slider's voltage should go smoothly from 0V to 11.2V then is amplified to 0V to 32V by the output amplifier.
  7. audioguru2

    Electronic Stethoscope

    The metalized film diaphragm of an electet mic is charged to about from 50V to 100V. As it vibrates by sound, its capacitance changes from a fixed plate and a FET transistor buffers the resulting AC voltage caused by capacitive voltage divider action. I said it was a high voltage because a...
  8. audioguru2

    Time division duplex led

    The display needs its lighted segments to have positive current and one or both of its common cathode wires need to be negative (usually grounded).
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    I said it before. Quote: "Q1 is supposed to conduct when the project is turned off and then it will immediately drop the output voltage to zero. The negative supply has low-value capacitors that discharge much quicker than C1, therefore Q1 becomes biased on." Maybe your C1 is defective and its...
  10. audioguru2

    Effects

  11. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Stanley, Your negative supply is fine. ;D Maybe your R17, R18 or P2 has the wrong value. :( Maybe your opamp U3 is damaged. :( Look at my sketch of the current regulator U3 section without any load current, and think about P2 turned down: 1) The opamp's inverting input pin 2 is 0V. 2) The...
  12. audioguru2

    i have a question

    The article explains pretty well how it works. D1 or D2 conduct if the input voltage exceeds the power supply voltage by a forward diode voltage drop (0.6V) and clamp the voltage at the output from exceeding +12.6V and -12V. R2 limits the current when the input voltage is too high. The 1/2W...
  13. audioguru2

    Effects

    There are similar projects in our Projects section.
  14. audioguru2

    Choice of op.amp. model

    The choice of a power amp IC depends on how much power you need and what is the impedance of your speaker. National Semiconductor, Philips and ST-Micro make hundreds of them. A few tutorials about opamps are in our Articles section. The positive and negative supplies need a bypass capacitor...
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Pigster, Welcome to our forum. ;D It sounds like the negative 5.6V supply comes up to its voltage too slow. Maybe R2 is burnt and has increased from 82 ohms. More info about R2 below. The negative supply connects to U2 which controls the output voltage. Q1 is supposed to conduct when the...
  16. audioguru2

    Electronic Stethoscope

    Maybe it is damaged. I recommend replacing it. Then how can you adjust the volume to match the sensitivity of your microphone and earphones? The circuit is designed for an electret microphone. It is a condenser microphone with a built-in high voltage charge and a FET transistor. R1 in the...
  17. audioguru2

    Choice of op.amp. model

    A 14 pin package is standard for ICs. 22 pins is not. If you need to null the input offset voltage then use a single opamp.
  18. audioguru2

    Electronic Stethoscope

    Hi UH, Welcome to our forum. ;D We have two Electronic Stethoscope projects, the 1st one doesn't work and the 2nd one does. Which one are you building? In the 2nd one, U1a has its input capacitively coupled so becomes a DC follower of its reference DC voltage on pin 3. Therefore the DC voltage...
  19. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Stanley, It sounds like the negative 5.6V supply at D7 isn't working. U3 is the current comparator and its output needs to be able to go to a negative voltage in order for D9 to pull the output voltage down when the current through R7 exceeds the current setting.
  20. audioguru2

    i need help extending the keys finder project. can someone help me out????

    Hi Logan, I purchased bags of tiny LEDs where the LED is about 0.05" in diameter and has flat leads coming out their bottom sides. They fit on a pcb with 0.1" leads spacing. They were red, yellow and green. They weren't bright white nor blue. I use them as low-voltage zener diodes. For a...
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