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  1. audioguru2

    0-30V Stabilized Power Supply

    The BD139 driver transistor Q2 will probably burn up. Also U2 will not be able to drive Q2 hard enough. R7 will need to have much less resistance and be much bigger. T1 and C1 will need to be much bigger.
  2. audioguru2

    0-30V Stabilized Power Supply

    The OPA445 high voltage opamps were used about 5 years ago. Today they are available only sometimes (Digikey has some today) and are very expensive (nearly $12.00US each). The new version has a choice of two inexpensive opamps that are available at many places in North America and maybe in Europe.
  3. audioguru2

    JFET Mic Pre Advise Please

    Most modern condenser mics have a balanced 600 ohms output so using fets at the preamp is useless. An input transformer in the preamp might pickup hum and has poor low and high frequency response. A transformer saturates at high levels. Input transformers might not be available anymore (remember...
  4. audioguru2

    JFET Mic Pre Advise Please

    Condenser mics are balanced and are fed 48VDC to polarise the diaphragm. Dynamic mics are also balanced. A mic preamp used an input transformer about 30 years ago but now they use an electronic circuit.
  5. audioguru2

    final year project

    Hi Hazel Anne, Many of your words are not English so we don't know what you are talking about. The output current from a piezo sensor is much too low to charge a battery.
  6. audioguru2

    0-30V Stabilized Power Supply

    Opamp U3 is the current regulator. The 0.47 ohm resistor R7 develops a voltage across it due to the load current in it and this voltage feeds the (-) input of U3. The (+) input of U3 is fed a variable voltage set by the current regulation pot. When the voltage from R7 is higher than the voltage...
  7. audioguru2

    JFET Mic Pre Advise Please

    Origionally, the circuit had a high output current so it could drive a fairly low inpedance load. Now its current is much less so it cannot drive a fairly low impedance load. Its input impedance is 10M ohms so why ruin it with an input transformer?
  8. audioguru2

    0-30V Stabilized Power Supply

    The current regulation simply reduces the output voltage to satisfy Ohm's Law.
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    A big knob has a large diameter so your hand can turn it easily a lot or a tiny amount. Because you can turn it a tiny amount then a fine tuning pot is not needed.
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    I would never use a separate fine pot. It would always be in the wrong position. Instead I would use a big knob for accurate leverage.
  11. audioguru2

    12V DC ==> 500 V &/OR 1000 V the best topology to this design?

    Again you forgot to say how much current. A car battery can supply 4000W (333.3A) for about 1 minute then the electrolyte boils and the battery blows up. What will you use 500V at 6.4A for?
  12. audioguru2

    bug detector

    The circuit had many errors. Some errors were fixed in the forum but other serious errors remained. I guess the project was deleted because it didn't work.
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    The two output transistors each must have a 0.33 ohm/2W resistor in series with its emitter to allow the transistors to equally share the current. The other ends of the emitter resistors are joined at the output of the project. They are shown on the latest schematic and described in the latest...
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

  15. audioguru2

    Are these two circuits equal?

    I think that if you are going to use a voltage regulator in a car then you should use one that is designed to be used in a car. I use the little LM2931 but there are many others and some are bigger with higher power dissipation and current ratings.
  16. audioguru2

    0-30V Stabilized Power Supply

    It doesn't have current limiting. Instead it has current regulation (constant current source) which is more exact. Ohm's Law says that the voltage must be reduced for the current to be regulated when the load resistance is reduced. For example if the voltage is set to 30V and the current is set...
  17. audioguru2

    Are these two circuits equal?

    The datasheets for the regulators show capacitors to keep them from oscillating,  not inductors. Their error amplifier has a high gain to keep the output voltage from changing. A regulator that works properly regulates its output voltage so inductors are not required.
  18. audioguru2

    12V DC ==> 500 V &/OR 1000 V the best topology to this design?

    You make no sense because you forgot to say how much current. You forgot to say if the waveform is square-wave, sine-wave or a modified square-wave. Are you making a simple high voltage circuit to make a Xenon bulb flash for a little camera? Please say all these details.
  19. audioguru2

    opamp roll-off

    According to the occasional PM's I get from Kevin, he is a human living in Texas. Maybe he didn't learn electronics in University like some of us.
  20. audioguru2

    opamp roll-off

    Low frequency opamps like the LM358 dual and LM324 quad use low power supply current which causes poor performance at higher frequencies. Their low current also causes 3% crossover distortion. I have never used a high frequency opamp. Most ordinary audio opamps perform very well up to 100kHz.
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