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  1. audioguru2

    0-30V Stabilized Power Supply

    The original circuit has many overloaded parts. Its transformer voltage is too low so its output at 3A is 25VDC, not 30VDC. We modified this project so that it is reliable and produces 30VDC at 3A. We showed a simple change that allows its output current to be 5A.
  2. audioguru2

    0-30V Stabilized Power Supply

    But R21 is supposed to be 10k and it connects pin 2 of U3 to R7. When current-setting pot P2 is minimum then R21 has a max of 0.5uA (for an MC34071 opamp) to 2uA (for a TLE2141 opamp) of input bias current which makes pin2 a max of 5mV to 20mV, not 95mV. This input bias current in R21 turns off...
  3. audioguru2

    0-30V Stabilized Power Supply

    R7 is 0.47 ohms so with 95.5mV across it the load current of the project is 203mA which is 28 times too high. The current should be only 5.6mA in R4 plus 1.2mA in P1 plus 0.56mA in R6. Check the few connections along the output of the project for a connection to something that is wrong. The...
  4. audioguru2

    0-30V Stabilized Power Supply

    Hi Fikic, With no load on the project, the output pin 6 of U3 should always be high at about +24V to +28V. So it does not reduce the output voltage through D9 and it does not turn on Q3 to light the LED. The slider of the current adjusting pot P2 applies a small positive voltage to the (+)...
  5. audioguru2

    0-30V Stabilized Power Supply

    I know that your circuit works wrong. I explained how it is supposed to work so you can fix it. 1) U3 works wrong so double-check that its inputs are not connected backwards or shorted together. 2) Make sure that the output pin 6 of U3 is not shorted to ground or to -1.3V. What is the voltage of...
  6. audioguru2

    0-30V Stabilized Power Supply

  7. audioguru2

    0-30V Stabilized Power Supply

    Of course it didn't work without C1. That is normal. it regulates the output current by reducing the output voltage which reduces the output current according to Ohm's Law. The LED should turn on only when it is reducing the output voltage. That is normal. The output voltage of U3 drops when it...
  8. audioguru2

    0-30V Stabilized Power Supply

    Your circuit has no output power maybe because you connected the collector and emitter of an output transistor or the driver transistors backwards. U2, Q2 and the output transistors are an amplifier that can have a load of 3A and the output voltage will drop only 5mV (0.005VDC) which is caused...
  9. audioguru2

    Variable supply using LM317 with 32Vrms transformer rating

    The datasheet for the LM317 shows that it reduces its max output current as the voltage across it increases above 15V. So if the input is 35V and the output voltage is very low then the max output current could be as low as about 200mA. With 15V across it and 1.5A of current then the little...
  10. audioguru2

    Power Amplifier for Guitar

    Resistance reduces DC current. Impedance basically reduces AC current from an AC signal. The guitar pickup with the Jfet has an output resistance of 6.8k ohms. If it drives an amplifier with an input impedance as low as 6.8k ohms then the signal is divided so that half of it is thrown away. You...
  11. audioguru2

    Power Amplifier for Guitar

    Since the OP cannot bias a simple transistor properly then I don't think he can use an opamp. The preamp for a guitar pickup must have a high input impedance of at least 1M ohms. His microphone premp did not have a high input impedance and your inverting opamp also will not have a high input...
  12. audioguru2

    Power Amplifier for Guitar

    In the other thread you posted the completely wrong schematic of a microphone preamp that will not work with a guitar pickup. I fixed it so it will work as a microphone preamp. It uses two little BC109 or BC549 transistors. I also posted the very simple schematic of a guitar pickup preamp that...
  13. audioguru2

    New to electronics

    I get datasheets from www.datasheetarchive.com . I can select a manufacturer. A 2N3055 is in a steel case and has a max allowed internal temperature of 200 degrees C. An MJE3055 is in a plastic case (T) and has a max allowed internal temperature of 150 degrees C. Their max allowed currents are...
  14. audioguru2

    0-30V Stabilized Power Supply

    That is normal when there is a load on the output of the power supply. When you turn down the current-setting pot then the current regulating circuit reduces the output voltage to keep the output current at the setting of the current adjustment pot. The LED lights to warn you that the output...
  15. audioguru2

    audio amplifiers

    I don't know why people use class-A audio amps. They waste a very high amount of power by getting hot especially when they are not playing. Some "odd" people add a class-A load to the output of an OPA034 opamp to "reduce" its 0.00008% distortion. They are crazy since 0.05% or less distortion...
  16. audioguru2

    0-30V Stabilized Power Supply

    When you turn the current adjust pot P2, measure the output voltage of opamp U3. It should stay high at about +22V so it cannot cause D9 to reduce the voltage at the input of opamp U2. Maybe D9 is leaking and possibly caused by light shining on it. Look at the datasheet for a BZX85C5V6RL, it is...
  17. audioguru2

    0-30V Stabilized Power Supply

    I didn't look at your pcb but the schematic is correct. But zener diode D8 has only 5.6mA in it so i specified a BZX79 one that is tested at 5ma. You used a BZX85 zener diode that is tested at 45mA and it might have poor regulation at only 5.6mA.
  18. audioguru2

    0-30V Stabilized Power Supply

    Here is my schematic and parts list for the 3A project again:
  19. audioguru2

    0-30V Stabilized Power Supply

    Maybe c8 is shorted.
  20. audioguru2

    0-30V Stabilized Power Supply

    Opamp U3 is a comparator. It compares the voltage at its inputs and its output is either high at about +24V or low at about -0.6V. When its output is low then it reduces the output voltage through D9 until the current is the same as the setting on the current-setting pot P2. It also turns on Q3...
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