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  1. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi No Worries, At a DC current of 3A, a 6800uF filter capacitor of a 60Hz mains that is full-wave rectified produces a ripple voltage of 1.85V peak which is a fluctuating loss of voltage which might cause hum at the output. If the mains frequency is 50Hz then the peak ripple voltage is 2.2V. Use...
  2. audioguru2

    Re: coaxial cable and GHz frequency

    Hi Eplanet, For you to measure the current from the power supply that powers your LNB you need its schematic and parts layout.
  3. audioguru2

    hydroxy gas power supply/separating oxygen and hydrogen from water

    Hi Steven, Are your batteries rated at 7A and 9A or at 7Ah and 9Ah? Ah is ampere hours. According to The Battery University on the internet, a SLA battery rated at 9Ah can supply 0.45A for 20 hours or 1.8A for 5 hours. It might not be able to provide 9A.
  4. audioguru2

    Re: need help asa

    The trimmer capacitor in the oscillator circuit tunes the transmitter's frequency. The trimmer capacitor at the output RF amplifier is tuned for a peak at 100MHz (the farthest range). When it is peaked at 100MHz (the middle) then the transmitter still works pretty good at 88MHz and at 108MHz...
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Mayhem, Of course Q2 and Q4 should have a base-emitter voltage drop of 0.7V to 1.2V when there is a load. They are emitter-followers. Yours must be shorted from base to emitter. Opamp U2 has an open-loop voltage gain of about 200,000 so it should amplify the small error to keep the output...
  6. audioguru2

    Re: need help asa

    Turn the trimmer capacitor with a plastic screwdriver with an FM radio tuned to the middle of the FM band near the transmitter. You will hear acoustical feedback howling when it is tuned to the radio's frequency. I have a cheap Sony Walkman FM radio that is overloaded by my FM transmitter and...
  7. audioguru2

    Re: need help please..

    R7 must be a potentiometer and is adjusted for a null in your voice that goes to your speaker. Your station's output audio amp is connected to its slider. Look at the datasheet for the TDA7052A to see how to connect its DC volume control at pin4. I think the gain is max (+35.5dB) when pin 4 has...
  8. audioguru2

    Electronics Hobby Projects and Circuit Applications

    Many of the projects were stolen from Red Circuits and are also here in our projects section.
  9. audioguru2

    Re: need help please..

    With a log pot, when the control is turned from max to half-way then the audio level drops -20dB so it sounds attenuated. With a linear pot turned from max to half-way the audio level drops only -6dB so it sounds almost the same. At the low end the log pot adjusts the low level volume. The...
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    U1 is an 11.2V voltage reference. The opamp has a gain of 2 and it multiplies and feeds the 5.6V zener diode D8. U2 is the main amplifier for the voltage regulator. It has a voltage gain of 3.074. It has a variable input voltage. U3 is the current regulator. It compares the voltage drop across...
  11. audioguru2

    white led

    If the LEDs are actually all 3.0V and divide the current equally then each 33 ohm resistor will have a voltage drop of 0.99V. Then if the battery is max at 13.55V the power transistor has a voltage drop of 13.55V - 9V - 0.99V= 3.56V. It will dissipate 3.56V x 0.96A= 3.4W. Any power transistor...
  12. audioguru2

    Re: need help please..

    The pot is supposed to be 22k. 20k to 50k will be fine and 10k and 100k might work.
  13. audioguru2

    Re: need help please..

    There is a big difference if you use the wrong type of pot as a volume control. Steal a volume control log pot out of an old radio or cassette player.
  14. audioguru2

    Re: need help please..

    A log potentiometer is a volume control. If you use a linear pot then most of the volume change will be at its low end and from half to max will make very little difference in volume.
  15. audioguru2

    hydroxy gas power supply/separating oxygen and hydrogen from water

    You must learn how to measure current with your meter. It must be connected in series with the load to measure the load current. Instead you were measuring the max shorted current from your battery. Of course it dropped slowly as the battery was being discharged. You need to connect the leads...
  16. audioguru2

    white led

    Hi Pier, The circuit has 300mA, not 960mA. A 2N3055 power transistor can dissipate up to about 70W if it has a huge heatsink. Why do you have battery-powered LEDs in your room? Don't you have electricity? Or do you live in a tree? ::)
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

    The TLE2141 opamps can also be used. Go to www.farnell.com and click on the flag of Brasil. But they also don't have either opamp. Maybe they can order them for you. They are in many countries. The Canadian/American one has EVERYTHING.
  18. audioguru2

    1.2 V PWm Signal

    That is a good PWM circuit. I made it for my electric model airplane but I used more modern and faster MC33172 dual opamps instead. I used a frequency of about 2kHz because I like to hear the motor whine. Connect it to your Zetex IC like this:
  19. audioguru2

    telephone transmitter again not working??

    If you power the telephone transmitter from a battery then it will either stop the phone from ringing or it will be destroyed by the high ringing voltage.
  20. audioguru2

    1.2 V PWm Signal

    There is no Mosfet. The 200k resistor is inside the Zetex IC. It is the collector load of the new transistor. A BC547 transistor is fine. The output of the LM324 goes up to about 7.8V when the supply is 9V and up to 4.8V when the 9V battery is nearly dead. So the base resistor should be about...
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