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  1. Audioguru

    Transistor Analysis

    You need to allow for the awful +/- 30% (!) tolerance of the resistor values inside that transistor.
  2. Audioguru

    MC34071

    The power supply is similar to the one that I fixed and I used MC34071 opamps. The TLE2141 opamp designed by Texas Instruments works the same as a MC34071 and is still made in a through holes package. The NJM5532 will not work in that circuit because its common mode input voltage range does not...
  3. Audioguru

    LM358 to make FM Audio Receiver

    Why do you think the power will be increased if you add more 2N4401 and 2N4403 transistors? Show how they would be connected. How loud do you want the radio to play? A cheap clock radio produces about 0.5W. An LM386 powered by a 9V battery produces 0.45W before clipping distortion becomes bad...
  4. Audioguru

    Power Dissipation Across A Transistor In Cutoff

    It is simple to calculate the base current. Don't you know that the base-emitter voltage for a modern silicon transistor is about 0.7V? Don't you know Ohm's Law? The datasheet says the range of the resistance in series with the base and the range of input voltage needed for the transistor to...
  5. Audioguru

    Transistor Analysis

    That transistor has a 10k resistor in series with its base. It saturates not very well (0.3V) when its input voltage is 1.8V or 2.5V. If the input voltage is higher then it will saturate better.
  6. Audioguru

    How to test a transmitter circuit?

    I chatted about that circuit a few minutes ago, maybe on another website and maybe by someone else in your school. It was also posted 12 years ago and did not work. I fixed it with 4 improvements: 1) Its audio transistor was not biased correctly saturated when the battery is new and was cutoff...
  7. Audioguru

    Power Dissipation Across A Transistor In Cutoff

    The datasheet for every transistor shows how much base current is needed to cause it to fully turn on (saturation). Since it is PNP then the base voltage must be a base-emitter voltage drop more negative than the emitter voltage for it to turn on.
  8. Audioguru

    Can anybody explain about how bjt works??

    An emitter resistor adds negative feedback, reducing the voltage gain and reducing non-linearity (reducing distortion).
  9. Audioguru

    Transistor Analysis

    This must be a little BCxxx European transistor since its base current is 1/20th the collector current for saturation. Most little 2Nxxxx American transistors specify a base current that is 1/10th the collector current for saturation. hFE is not used for saturating a transistor. Power...
  10. Audioguru

    LM358 to make FM Audio Receiver

    An LM358 is no good for audio because it was made to have very low power consumption then its output transistors do not have enough idle current which causes crossover distortion, hiss noise and poor high frequency slew rate. An LM358 has trouble with normal audio frequencies above 2kHz. The...
  11. Audioguru

    Led Flashlight Help

    A cheap Chinese "super heavy duty (carbon-zinc)" battery that is leaking in its package after sitting on a store shelf for months is not what I call a normal battery. All 24 very bright LEDs in my cheap torch are still fine but its on-off switch sometimes makes a poor connection.
  12. Audioguru

    Finding a good soldering iron....

    I have used multi-core flux in 63/37 solder all my life and I have never washed off the flux after soldering. All my circuits, even ones made 55 years ago are still fine.
  13. Audioguru

    Vacuum in a Can

    I think my tummy has a vacuum when I am hungry.:)
  14. Audioguru

    Fm receiver circuit .

    The schematic is missing a solder dot at the base of T1. It should be obvious that T1 operates as a common base amplifier since C1 grounds its base. T1 is a variation of a Colpits oscillator. Signals do not go up and down. T1 is never turned off, it oscillates all the time. As the FM signal...
  15. Audioguru

    Dynamic mic amp as clap switch

    Sorry, I do not have time to teach you the basics of transistors.
  16. Audioguru

    Dynamic mic amp as clap switch

    A CD4027 has two flip-flop circuits inside. It has low output power but it can drive a transistor or Mosfet for lots pf power. What will it drive? There is no such thing as an electric mic. Maybe you have an electret mic that is a condenser mic with 48V stored in its electret material, and a...
  17. Audioguru

    LM358 to make FM Audio Receiver

    Do you know Ohm's Law? Voltage divided by resistance = current? Assuming that the speaker is 8 ohms and you want a peak voltage of 3V in it then the current is 3V/8 Ohms= 375mA. The datasheet for the LM386 power amplifier shows that it can produce a little more than 375mA but the datasheet for...
  18. Audioguru

    Finding a good soldering iron....

    Thanks for your offer but you are on the other side of the world (between Beijing and Ronne Ice Shelf?) from me. It looks like you are in Australia, MATE!;)
  19. Audioguru

    Finding a good soldering iron....

    For years I used Ersin 63/37 multicore (British?) and it worked very well and I liked the aroma of its flux. I was running out so I bought Kester 60/40 but I do not like its behaviour. Now I have MG Chemicals 63/37 rosin core but its flux does not work as well as the Ersin.
  20. Audioguru

    Dynamic mic amp as clap switch

    During the clap sound, the relay will flip and the sound that is still occurring plus its echo will cause the relay to flop back to the original position and maybe this will cause the relay to flutter a few times. You need a flip-flop circuit that latches at the beginning of a sound. Your first...
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