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  1. audioguru2

    Electronic Stethoscope

    Hi Prateek, The TL071 and TL072 are very common and cheap in North America. They have been used in audio equipment for about 20 years. A TL071 costs a little more than a 741. A TL072 dual costs less than a 741. An LM833 dual is also low-noise, and costs a little more than a 741. Can you get...
  2. audioguru2

    Primary current waveshape

    Hi Bakr, Your transformer is a high-Q resonant circuit that probably "rings" at a very high frequency. You can take advantage of this (like a TV's HV supply and a car's spark coil) by tuning the transformer to the oscillator's frequency with a capacitor in parallel with the primary. Around 22nF...
  3. audioguru2

    Electronic Stethoscope

    Hi Doctor Emad, I am sorry to hear that your corrected circuit doesn't work properly yet. The first thing that should be done is to use shielded cable to the microphone. It is very important. Non-shielded wire would pickup a lot of mains hum that can overload U1 due to its high gain. Whenever I...
  4. audioguru2

    Low-pass Filter?

    Hi Mark, It is good that you are from The Phillipines because Ronnie (called Rhonn, and his handle here is Kasamiko) is also there. He helped me fix this 500W inverter and he has many inverter circuits. His e-mail address is on this schematic of the fixed inverter that he drew.
  5. audioguru2

    Low-pass Filter?

    Hi Mark, Welcome to our forum. Are you from St. Phillips Island, The Phillipines or Philadelphia? I'm up here in Canada, no snow here, yet. The 500W inverter that is mentioned above is a fix to a defective one in our Projects section. A member has reported that the fixed version works very well...
  6. audioguru2

    Low-pass Filter?

    Which project did I redesign from scratch? Just simple little fixes, that's all. The power supply project has only 1 additional output transistor added, plus 2 emitter resistors to balance them. Same circuit, but with proper parts selection. No redesign. What about the 500W inverter project...
  7. audioguru2

    oscope to tv

    Hi Absolution That's right, the 'scope's picture wasn't very bright since its tiny dot must "paint" the whole screen. It was much brighter when I made the picture smaller. I used a constant current source transistor instead of a simple resistor for the vertical sweep, and the picture was...
  8. audioguru2

    Low-pass Filter?

    Sure MP, a) My heart is fine and I don't need this
  9. audioguru2

    Electronic Stethoscope

    Hi Guys, As a review, I have posted analysis of faults with this project and my corrections in the Theory Section of this forum, here: Opamp or Power Amp? http://www.electronics-lab.com/forum/index.php?board=15;action=display;threadid=1630 Low-pass Filter...
  10. audioguru2

    Extra Parts

    Hi Guys, In another post we have discussed that components of a project are not needed but someone disagreed. This circuit consists of 741 opamps U2 to U4. U3 is "supposed" to buffer the output of U2 from the loading effect of R11 which is 2.5K. R9 is "supposed" to limit the current from the...
  11. audioguru2

    Low-pass Filter?

    A simple error was made on the original schematic since the junction of C3 and R7 should be connected to pin 6 of the opamp. Then it will be a Sallen and Key Equal Component Butterworth Low-pass Filter. Do you think that C3 should have twice the value of C4? Only if the opamp has a gain of 1...
  12. audioguru2

    Low-pass Filter?

    Hi Guys, In another post we have discussed why this part of a project doesn't work as a low-pass filter that is described in the project's text, and produces severe distortion and noise. The original part of the schematic is on the left side, and I re-drew it on the right side to make it easier...
  13. audioguru2

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

    Hi Chester, I'm glad that the current regulator works great now. Yeah, I'm sorry that I mis-read your post, but maybe you did too. The voltage regulation is actually quite good, dropping 40mV (not 5mV as you say) and I bet that it is much better if you measure right at the regulator's output...
  14. audioguru2

    Schematics Variable current 12v 60A to 0A

    Hi Ante, Your prize will make "only" 16M colours, and its white will be much better than a white LED.
  15. audioguru2

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

    Hi Chester, Your rectifiers have a higher voltage drop than I expected. Aren't you using a 10A or more rectifier bridge module? With the regulator set to 29.99V it loses voltage regulation when its output drops to 28.95V with a 1.2A load. I'll bet that the output has a lot of ripple. The...
  16. audioguru2

    Electronic Stethoscope

    Hi Prateek, How is the level of the heartbeat signal? It is easy to change. As I said before, the 741 is a lousy, old and noisy opamp, especially for a low-level microphone preamp. A modern low-noise opamp, like a TL071 will be much better. Actually, I would use a dual, TL072 for U1 and U2 in...
  17. audioguru2

    part replacement

    Hi Black Wing, A TL072 (Texas Instruments) will work fine. It also has FET inputs, low distortion and lower noise. Same pin-out.
  18. audioguru2

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

    Hi Ante, Good point! If your power supply isn't reliable with its patrts operating well within their ratings, it is dangerous to your health and to your load.
  19. audioguru2

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

    Hi Chester, Welcome to our forum. On your website I like your propclock and big sparks. Good luck with your 15KW sine-wave inverter project. This 30V/5A lab power supply: If your custom-wound transformer produces 28VAC with a light load, then 44V-rated opamps are almost at their limit. Just...
  20. audioguru2

    oscope to tv

    Hi Absolution, I have done it and it worked well. I don't know about yours, but my country uses the simple NTSC television standard. If yours is PAL or SECAM, then it will be a lot of trouble. Of course I used the tuner and sync separator from a TV. Do you want to make almost a whole TV that is...
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