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  1. audioguru2

    0-30 Vdc Stabilized Power Supply

    Which schematic are you using? Years ago when I replaced the low voltage TL081 opamps with higher voltage MC34071 or TLE2141 I replaced the D7 zener diode with  two diodes so that the negative supply is only -1.3V. The 0V reference (zero point) for making measurements has always been the...
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Tintin, Now you say you measured 27VAC from your 24V transformer when its load current is low. Then it is cheap and has a high resistance so they made its voltage 27VAC instead of if it had low resistance and an output closer to 24VAC. Or maybe the voltage of your AC electricity is higher...
  3. audioguru2

    0-30 Vdc Stabilized Power Supply

    This project will not produce 30.0VDC at 3.0A with a 24V transformer. It might produce 25VDC at 2A with a lot of unregulated ripple.The transformer must be 28VAC or 30VAC at 4.2A. A 24V transformer will produce about 25VDC when it has a small load current which has a peak of 25V x 1.414= +35.4V...
  4. audioguru2

    0-30 Vdc Stabilized Power Supply

    A solderless breadboard has intermittent contacts that cannot handle the high currents of this project. The many rows of contacts and wires all over the place have capacitance between them that frequently causes a circuit like in this project to oscillate at a high frequency. In my career I...
  5. audioguru2

    acid_circuit

    Why are you using an old fashioned vented lead-acid battery? Most circuits today are powered by rechargeable Ni-MH or Lithium batteries that have no acid.  
  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    Every opamp has an input offset voltage error. Single opamps like the recommended MC34071 and the TLE2141 have input offset voltage adjustment pins. The project uses trimpot RV1 to null the offset voltage but your MC34072 does not have offset adjustment pins. Since your MC34072 has two opamps...
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    The Chinese power supply uses relays to switch the transformer voltage into voltage ranges so that the output transistor does not get too hot. I do not know if any parts are overloaded and I do not know how good or bad is its regulation. Its LM741 opamps were designed 50 years ago (!).
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    Your photo of a no-name-brand Chinese power supply does not show any specifications and does not show its schematic and parts list. The photo shows its 30VDC output when its current is zero. The defective Greek kit and Chinese copies do that but cannot produce 30VDC at 3A. Instead they produce...
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    This project has been copied and is available for a very low price on ebay, Banggood and Amazon.              But it has all the problems of the original kit from Greece. Many parts are overloaded and fail soon. It does not produce 30VDC at 3A. It looks like the Chinese people who copied it...
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    The original project had many overloaded parts including the power transformer. It used TL081 opamps but your TL071 opamps are simply TL081 opamps selected fo low noise (audio applications). Their absolute maximum supply volyage is 36V but this project with a 24VAC transformer produces about...
  11. audioguru2

    0-30V 0-3A Latest Data Discussion

  12. audioguru2

    0-30 Vdc Stabilized Power Supply

  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    Since it was years ago I do not remember which page of which thread has version 6 or 7. I have the schematic and parts list of version 6 here:
  14. audioguru2

    Build A Wooden Portable Speaker Box

    The speaker drivers look tiny, 2 inches or 3 inches in diameter like a cheap clock radio? No bass. The PAM8403 amplifier IC produces 3 Whats with high distortion into a 4 ohm speaker per channel or 2 Watts at less but still audible distortion when the supply is 5V. Have you heard the Bose...
  15. audioguru2

    0-30V Stabilized Power Supply

    The TLE2141 opamp has PNP input transistors so that the outputs work with an input as low as 0V. Then you must pull the input down and not let it float up. Your multimeter pulls the input of the opamp down. The maximum input bias current for a TLE2141 opamp is 2.1uA that tries to pull the input...
  16. audioguru2

    0-30V Stabilized Power Supply

    The middle opamp in Liquibyte's schematic is the 11.2V reference because it uses a 5.6V zener diode and it has a gain of 2 times. The voltage setting pot R27 is simply a voltage divider that feeds 0V to 11.2V to the non-inverting input pin 3 on the opamp on the right side. The gain of this opamp...
  17. audioguru2

    0-30V 0-3A Latest Data Discussion

    I cannot remember my fix for the "on" voltage spike. If you remove the negative supply then you will not be able to limit shorted output current less than about 0.43A since the transistor that replaces the diode cannot go lower than its max saturated output of about 0.2V. 0.2V/0.47 ohms= 0.43A.
  18. audioguru2

    0-30V Stabilized Power Supply

    Nand, Simply calculate the amplitude of the 120Hz (or 100Hz) ripple that will be produce when the load draws 3A. It won't be regulated with that much ripple.
  19. audioguru2

    0-30 Vdc Stabilized Power Supply

    You must change the values of the parts that try to produce volts and amps outputs higher than you will get. You can calculate the maximum regulated output voltage, maximum regulated current and maximum heat produced by the transformer then try adjusting the calibration pots to see if they will...
  20. audioguru2

    0-30V Stabilized Power Supply

    Audio amplifiers do not need a voltage regulator or a current regulator. A car radio amplifier is powered directly from the car battery with no voltage regulator but the low current radio parts might use a simple little voltage regulator. 14V at 6A is 84W!  One amplifier produces a maximum...
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