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  1. audioguru2

    regulated 12 v dc and 500 mA current o/p

    Hi Absolution, The datasheets for the 78xx and LM317 show that a PNP power transistor can be used as a "booster" for more output current.
  2. audioguru2

    Sine wave inverter

    Hi Absolution, When you say "tapping at the collector", do you mean to add a capacitor to ground to form a simple single-stage low-pass-filter, creating a maximum of 90 degrees of phase shift? If your bridged amplifier is fed with a square-wave, its output with that simple filter will be a...
  3. audioguru2

    Opamp or Power Amp?

    Hi again Guys, Perhaps the author of this audio amplifier meant to use an LM386 1/2W power amplifier IC instead of a 741 opamp, but forgot and called the LM386 a 741 by mistake. Then later realized that the pin numbers were wrong for a 741 and changed them. The LM386 has advantages in this...
  4. audioguru2

    Opamp or Power Amp?

    Hi Guys, In another post we have discussed why this part of a project doesn't work at all, or produces severe distortion and noise. This audio amplifier's input is near line level, and its output load is an earphone, 8 ohms or more, from a cell phone, home stereo or Walkman. Why doesn't this...
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Zwieke, That is an excellent cap that is perfect as C1 in this project. Google quickly found "BC Components" and their datasheet shows that pin 1 is positive and pin 5 is negative. The bottom view is here:
  6. audioguru2

    Electronic Stethoscope

    Thanks Doctor Emad, Your new construction will prove that the corrections work well. The same corrections that were discussed nearly one year ago by other members at the beginning of this thread. They "saw" the errors like I did, but also didn't build it to prove it.
  7. audioguru2

    Electronic Stethoscope

    This original circuit doesn't work here, and doesn't work on the original author's web site. The same complaints about it are there too. Why not make a simple correction to make it function and make a few more corrections and changes to make it improved? The professional doctors who use it don't...
  8. audioguru2

    Electronic Stethoscope

    That's right, his circuit "worked", but not very well.
  9. audioguru2

    Electronic Stethoscope

    Hi Doctor Emad, The original project has some errors that you can easily correct on your circuit: 1) Connect pin 6 of U2 to the junction of C3 and R7. 2) Use an LM386 for U5 and swap its pins: pin5 is output and pin6 is +9V. Do not connect pin 7. The LM386 has built-in feedback and biasing to be...
  10. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    Hi Asciiwhite, Ask Hammond for a sample, but you offer to pay to ship the heavy thing. They are in Guelph, Ontario, Canada. Once they gave me an expensive telco hybrid transformer.
  11. audioguru2

    need help in fm transmitter

    Hi Keile, Didn't you install a trimmer cap? It is very important and the author's PCB shows a value range from 5pF to 40pF. It is used to tune the transmitter's FM frequency. Did you jump here from another post about remote control? This simple circuit's FM frequency changes as the battery runs...
  12. audioguru2

    Electronic Stethoscope

    Hi Emad, That is good that you modified the original circuit to make it work fine. You are clever to change it so that U5 is properly biased and powered. How is its noise level? Where did you add a 2.2K variable resistance? What impedance are your earphones?
  13. audioguru2

    need help in fm transmitter

    Hi Keile, Of course the 28p cap affects the parallel resonant circuit, but may have a value that is much too high. What is the total range of values of the trimmer cap "Tr" that is in parallel with it? Have you seen the many FM transmitters in the "RF Circuits" of our Projects Section? Click on...
  14. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    Hi Asciiwhite, Newarkinone, or worldwide Farnell, has a nice Hammond 182H15 toroid with that rating. It has a 117/234V dual primary and 15/30V dual secondary. They also may have others. Hi Inferno, You are correct.
  15. audioguru2

    high voltage resister devider

    Hi Ante, You are correct. The 48uA here is only 1/100th of the current (5mA) that a Ground Fault Interrupter is required to trip at, to prevent electrcution.
  16. audioguru2

    high voltage resister devider

    Hi Ante, I also thought of using the 10M meter as part of the voltage divider, but rejected it since it would be a serious and lethal hazzard if the meter's leads became loose during HV operation. :o Hi Steven, You must be certain that your meter's input resistance is 10M or my calculation...
  17. audioguru2

    LM317 Variable power supply

    Sure MP, But you forgot that the IC's die heats 50 degtees C above the ambient temp of a nice and comfy 25 degrees, so the die's temp is 100 degrees (not 75) which is pretty close to its limit. Don't enclose it! Are you going to make a custom transformer to give exactly 3.0VDC above the output...
  18. audioguru2

    high voltage resister devider

    Hi Sparky Steven, With your meter showing 240V, and if its input resistance is 10M (look it up, it is in parallel with your 10M measurement resistor), then your actual high voltage is a whopping 47,760V! ;D ;D ;D
  19. audioguru2

    high voltage resister devider

    Hi Steven, Good insulation, you'll not have any arcing on that stack. ;D If your digital multimeter has a 10M ohm input resistance, then the voltage that it shows is only 1/2 of what it actually is. ::) I'm sorry, but your math is wrong. 100 times 28.3V is not 28.3KV. It is only 2.83KV. But...
  20. audioguru2

    LM317 Variable power supply

    Hi MP, OOOps, sorry, I forgot. You are probably using a fan or dry ice to cool your over-heated LM317. Then 1/2A output is easy.
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