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  1. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Ta, You have the collector and emitter of Q2 reversed. Its collector should connect to the positive unregulated 31.8V supply. Q2 might be destroyed since it had a high power in its base-emitter junction that isn't designed to handle power. U2 also might be destroyed since it probably got too...
  2. audioguru2

    3dB point or pole

    Hi Walid, A 3 dB point is the frequency that the stage's output is down -3dB from the output at much lower frequencies. -3dB is half power or 0.707 times the voltage. A pole is an RC lowpass filter caused by the "Miller capacitor" of a transistor's collector-base capacitance. Opamps have a...
  3. audioguru2

    0-30 Vdc Stabilized Power Supply

    If you have a big heatsink and the current regulator works, they shouldn't burn in this modified circuit. I never smelled a burnt metal one. Aren't you using transistors with the metal TO-3 case? Yes.
  4. audioguru2

    Led display Digital Voltmeter question

    MP, Intersil also have an improved one, also with guaranteed stability like Maxim's. Which one did you try and are people complaining about Intersil's old original one?
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Ta, Your negative supply is fine. Let's fix the output voltage without a load when it is 19V instead of zero: 1) With the voltage pot turnsd down to zero, the slider's voltage is 0V, isn't it? 2) Then the input pin 3 of U2 is also 0V, isn't it? 3) Since the output voltage is 19V, then the...
  6. audioguru2

    LIGHTENING STRIKES

    I would add a few more zero's. ;D
  7. audioguru2

    BASIC FEEDBACK THEORY QUESTION

    No Kevin, Differential inputs are used so that they can be exactly the same, for very low input offset voltage and drift. Also the differential inputs allow negative feedback to be applied, resulting in cancellation of any non-linearity and distortion between the amplifier's input and output.
  8. audioguru2

    OFFSET NULL ADJUSTMENT

    Hi Bjorn, Audio amplifiers without an offset adjustment use a balanced differential input with an input offset voltage of a very small amount. They use a capacitor on their negative feedback to ground voltage divider so that the amplifier has a gain of only 1 at DC, and the input offset voltage...
  9. audioguru2

    BASIC FEEDBACK THEORY QUESTION

    Hi Walid, The differential input voltage is the voltage between inputs, and if the amplifier has an infinite gain would be zero when negative feedback is applied. ;D
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Ta, Your project has a few problems. Maybe its -5.6V supply section isn't working. Isn't the voltage of pin 4 of U2 -5.6V with and without a load?
  11. audioguru2

    Replacement of two components

    Yeah, unlike an accurate single frequency crystal, a ceramic filter for an FM IF is wideband, about 180kHz. You don't need an inductor, a 100k resistor will provide plenty of isolation. Your BB143 substitute has a very low capacitance and probably won't work in this circuit. A BB809 has much...
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    Then your pots are OK. If you have the output voltage adjusted for 30V without a load then with a 30 ohm load (1A) what voltage does it drop down to when the current pot is set to max? With a 30 ohm load, when you adjust the output voltage upwards, is there a point where the voltage doesn't...
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Sallala, Welcome back! ;D You are going to end up with a power supply that works very well.
  14. audioguru2

    Led display Digital Voltmeter question

    Maxim's improved IC is much more stable than Intersil's original one. ;D
  15. audioguru2

    calculator to TV remote conversion

    Hi Shri, You can use the keypad matrix from a calculator but not much else.
  16. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Ta, It sounds like you have a bad pot. Measure the voltage on its slider when you turn it. The voltage should change smoothly and proportionately from zero to about 11.2V. Another bad pot? Maybe your pots are from the same bad batch. Try another manufacturer. ;D
  17. audioguru2

    Replacement of two components

    Full deviation for an FM station is plus and minus 75kHz, so 1/9th is only 8.3kHz which is possible by shifting the wideband ceramic filter's frequency. The varicap operates at about 4.5V in this circuit, right where the BB143 that you recommend has a sharp bend in its capacitance curve. It...
  18. audioguru2

    cd4541 rc timing calculation

    Thanks, MP ;D
  19. audioguru2

    Problem with my breadboard

    If your circuit operates at high frequencies, have you included the breadboard's capacitance between tracks, and the inductance of its jumper wires into your simulation?
  20. audioguru2

    Silly Question

    The other row is completely electrically separate from the 1st row. Use it if you need something else switched. ;D
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