Search results

  1. audioguru2

    0-30 Vdc Stabilized Power Supply

    Maybe you have the base and emitter pins of Q4 connected backwards. With Q4 removed then the output comes from R16. But the current through R16 is very low and might not be enough current to light the LED when the output is shorted.
  2. audioguru2

    bjt / jfet / mosfet as input in audio amplifier

    This is a common high input impedance preamp for a guitar that uses a Jfet:
  3. audioguru2

    infrared alarm

    You can use an IR detector IC like is used in TVs and DVD players. One 555 drives a couple of IR LEDs at the ultrasonic frequency of the IR detector (36kHz to 56kHz) and the second 555 modulates the first one to produce bursts of ultrasonic pulses as shown in the datasheet for the IR detector IC.
  4. audioguru2

    transistor biasing

    The beta of a 2N3904 doesn't change more than 3 times from its spec'd minimum of 100 to its spec'd maximum of 300. So if the base bias voltage divider has a current of 10 times the typical base current then the divider current is still 5 times the minimum base current which is fine.
  5. audioguru2

    transistor biasing

    The datasheet for a 2N3904 has a curve of its typical input impedance (its hfe x its internal emitter resistance). At 1mA its input impedance is only 3.9k ohms when its emitter resistor is bypassed for very high voltage gain. Its base current is typically 4.3uA so the biasing voltage divider...
  6. audioguru2

    transistor biasing

    Low current in a transistor does not cause bias drift. Improper design does. The worst possible way to bias a transistor is to ground the emitter and feed current to its base with a resistor from the positive supply. Each transistor has a different current gain so some will be saturated and...
  7. audioguru2

    0-30V Stabilized Power Supply

    A dual supply is two supplies. Make two. Maybe you want a dual polarity supply which has plus and minus outputs. Then simply make two of this project. One for plus and the other for minus.
  8. audioguru2

    Program launch: "Get Paid to Publish your Project!"

    It is a "gentleman's agreement" that you will not publish your project elesewhere. It will be too expensive to sue you if you break the agreement but you will probably be banned from here. I submitted a few projects here when there was a contest. I did not win but it doesn't matter because I am...
  9. audioguru2

    Found good projects

    The schematics are simply stolen from other websites. Some work and others do not work. Most of the audio circuits are from www.redcircuits.com and work properly. The Simple Inverter circuit is also here and it does not work. The Opamp Radio also does not work.
  10. audioguru2

    0-30V Stabilized Power Supply

    Each output transistor will have a max current of 778mA. At this current their minimum current gain is 60 so the driver transistor must supply 117mA and will need a heatsink. A TIP3055 is too slow for the driver and its minimum current gain is too low. Use a BD139 transistor instead. 
  11. audioguru2

    0-30 Vdc Stabilized Power Supply

    It sounds like you made the original circuit that has many problems. A few years ago we discussed why a BD139 transistor works better than a TIP31. Why don't you make the latest corrected version that is talked about in this forum and its shematic and parts list have been posted many times?????
  12. audioguru2

    0-30V Stabilized Power Supply

    One guy used this project to power a high frequency (hundreds of kHz) switching power supply. The electrolytic capacitor C7 on the output blew up due to the high ripple current in it. A film capacitor will not blow up and your low PWM frequency will be gentle to a film output capacitor.
  13. audioguru2

    Quick Heaters

    Your numbers are wrong. 4V at 500A is 2,000W. But a big soldering gun uses only about 100W.
  14. audioguru2

    Advanced Battery Technologies

    A calcium battery?? Lithium-polymer is much better. Since you are talking about calcium, when I was a teenager I became crippled. I could barely walk and could not run fast anymore. The doctor chopped off a calcium deposit on a bone in my ankle and then I was fine. The scar is barely visible...
  15. audioguru2

    5000 watt stereo amp

    I think the project is a joke. You need only about 100W RMS per channel in your home to be very (extremely?) loud. 5kW is used at an outdoors rock concert. The people up close are deafened.
  16. audioguru2

    0-30V Stabilized Power Supply

    The voltage-setting pot adjusts the output voltage from 0.0V to 30.0V. The current regulating circuit adjusts the current by using U3 and D9 to reduce the voltage at the input of U2, exactly the same as the voltage-setting pot.
  17. audioguru2

    0-30V Stabilized Power Supply

    Your power supply project has a fault. The voltage is supposed to be adjusted down to 0.0V. Since the current regulation causes the voltage to correctly go down to 0.0V then since it reduces the voltage from the voltage-setting pot to 0.0V then your voltage-setting pot does not produce a low...
  18. audioguru2

    0-30V Stabilized Power Supply

    The circuit works perfectly with TLE2141 opamps. Since your minimum output voltage is 1.1V then maybe your voltage-setting pot goes down to only 1.1V/3= 0.358V (the output amplifier has a gain of  3.074).
  19. audioguru2

    0-30V Stabilized Power Supply

    Which opamp do you have for U2? In the latest circuit the opamp must be an MC34071 or TLE2141 which have inputs that work at 0V and have outputs that go down to 0V. Ordinary opamps will not work at 0V.
  20. audioguru2

    help with an idea

    The transmitter is transmitting all the time so its battery will not last long unless it is huge. The receiver will be receiving all the time and will also need a huge battery unless you make it "sleep" most of the time then wake up for a moment when it tries to receive a signal then it sleeps...
Top