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  1. audioguru2

    alarm circuit using lm555

    The 555 is wired completely wrong. I corrected it. The thyristor makes the buzzer buzz continuously until its power is turned off. The buzzer buzzes at its own frequency. The 555 is supposed to be a timer to allow you to exit before the alarm goes off. I added a transistor as a gate to stop the...
  2. audioguru2

    4 watt fm transmitter

    Hi Frobnic, Welcome to our forum. ;D We have two "4W FM Transmitter" projects. Which one? I think it is the simple one with only 2 transistors. I don't think its output will be 4W unless you use a 16V supply and the output transistor gets extremely hot. The oscillator transistor will also get...
  3. audioguru2

    12 V DC to a 220V AC Inverter AMplfier Design

    Your inverter will be about 80% efficient. So 150W to the load and 38W of heating. Get a transformer rated for 188VA or its amps is 188/12= 15.7A. The higher peak current in the Mosfets is only momentary.
  4. audioguru2

    problem in oscillator part

    RF circuits at high frequencies must be made with very short wires to reduce capacitance between parts. Also long wires have too much series inductance for high frequencies. I used stripboard and other people have made a pcb. All semiconductor manufacturers make a low dropout 5V regulator like...
  5. audioguru2

    schematic sansui au-2900

    It looks like a big amplifier but wow, it has an output of only 15W per channel.
  6. audioguru2

    LM338/LM318 Not enough power. Vref drops!

    Maybe you got counterfeight ICs. Please post your circuit's schematic. The LM338 is a voltage regulator with a rock-solid output voltage without oscillations. It doesn't need a huge output capacitor but needs to have a small one as shown on its datasheet. The LM338 should pass about 9A before...
  7. audioguru2

    3 Channel Spectrum Analyzer - question

    One LM3900 has all four opamps inside. They are different from "ordinary" opamps. If ordinary opamps are used then the circuit will need to have some small changes. We can answer your questions here. The circuit's schematic has errors. The errors will cause mal-function and might cause damage...
  8. audioguru2

    transistor off

    The datasheet shows the current stays at about 33A if the drain voltage changes from 3V to 25V. It is a "typical" Mosfet so the gate voltage is only 5.5V instead of 10V.
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    Before you said the output was +33V with Q1, and 0V without Q1. What is the putput voltage and what is the voltage of pin 6 of U2 when the voltage pot is turned? Also, what is the voltage of pin 6 of U3 when the voltage pot is turned?
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Good. The zener diode and resistors are 5% so it is fine. The slider of P1 connects through R8 and R9 to pin 3 of U2 which should change from 0V to 11V when the pot is turned. Does the output voltage go from 0V to about +32V when the P1 pot is turned? Did you find out what was wrong with Q1?
  11. audioguru2

    0-30 Vdc Stabilized Power Supply

    You said pin 6 of U1 changes from 0V to 9.9V when turning the voltage pot. That is wrong. Pin 6 of U1 should remain at 11.2V and the slider of the pot should change from 0V to 11.2V.
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Eggy, If you remove Q1 then the circuit should work properly. Q1 quickly reduces the output voltage to zero when the project is tirned off, so that the output voltage doesn't rise. Pin 6 of U2 should be about 1.4V higher than the output voltage without a load. U2 and the output transistors...
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Eggy, Welcome to our forum. ;D Q1 is not supposed to make the output voltage high. It is supposed to make the output voltage zero when the project is turned off. Q1 does not have a positive supply. Maybe the base of Q1 or one of its base resistors is shorted to the positive supply. Then Q1...
  14. audioguru2

    Slow E-Lab!

    Hi Ante, I agree that this site is extremely slow. It has been variably fast and slow for a few weeks but now it is so slow that many times I think it doesn't work anymore.
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Re-calculate and replace every part in it. If it is set to 10A and the output voltage is set low or it is shorted then the output transistors must dissipate 420W. Use 6 output transistors on huge heatsinks with fans, use 3 driver transistors, add a pre-driver transistor and make many resistors...
  16. audioguru2

    problem in oscillator part

    I used American parts for my FM transmitter. Can you get American parts in your country? This is the schematic with parts numbers for my FM transmitter:
  17. audioguru2

    transistor off

    A Mosfet turns on with a voltage between its gate and its source. When it is turned on then a current flows fbetween its drain and its source, the amout of current depends on the Mosfet (they are all different, even it they have the same part number), the gate to source voltage, the load...
  18. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Steve, The project is a kit. It overheats and does not have 30V/3A output. I don't know what the kit maker does about complaints to them about the kit. We leave the original project in case somebody has built it and for us to talk about it. If somebody builds the improved version and updates...
  19. audioguru2

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

    Hi Boco, Welcome to our forum. ;D We have another long thread about our 0V-30V/3A power supply project. It had problems so I suggested a few improvements to fix it. I have posed my suggested parts list many times in the other thread. 5A is not much more than 3A so the improved circuit is the...
  20. audioguru2

    Salt-taster

    Hi Walid, An LED is a semiconductor. Semiconductors have a wide range of forward voltage, and it changes with current. The red LED that I use has a range of forward voltage from 1.5V to 2.4V at 20mA. Mine were all made at the same time and have a forward voltage of 1.75V at 20mA.
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