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  1. audioguru2

    Transistor base current

    A 741 opamp is 42 years old and was not made for quality, it was made to be the first opamp with an internal frequency compensation capacitor. Its spec's are at a supply of plus and minus 15V, not with lower voltages. Its output has poor response above only 9kHz at full output (28V p-p). It is...
  2. audioguru2

    0-30V Stabilized Power Supply

    Glen, That old version of this power supply project was made years ago when OPA445 high voltage opamps were available. Its 30VAC transformer makes about 31VAC without a load and the rectified peak voltage on C1 is 42.4V. Two of the opamps also have the -5.6V supply so their total voltage is 48V...
  3. audioguru2

    0-30V Stabilized Power Supply

    The original project has many errors. Changing the opamps to MC34071 or TLE2141 opamps with a max allowed supply of 44V fixes only one problem. The tiny poorly cooled Q2 transistor will melt! The overloaded transformer might melt or catch on fire. Many of the resistors get too hot. The main...
  4. audioguru2

    0-30V Stabilized Power Supply

    The version with the OPA445 high voltage opamps is an old version. Use the latest version that uses more common MC34071 or TLE2141 opamps.
  5. audioguru2

    Projects for a newbe

    I don't like schematic drawing software that makes a negative image with a black background. Also ones that have a grid of dots all over the schematic. Also ones that have only one line for each junction dot instead of up to four lines for one junction dot.
  6. audioguru2

    0-30V Stabilized Power Supply

    Connect the (-) wire of the fan to one 12V wire of the transformer. Connect the anode of a diode to the 12V tap on the transformer. Connect the (+) wire of the fan to the cathode of the diode. The current rating of the diode must be at least the current rating of the fan. If the fan hums or...
  7. audioguru2

    0-30V Stabilized Power Supply

    Hi Sing, Rectify the 12VAC tap on your transformer with one diode and listen to see if the fan hums. If it hums then filter the rectified 12V to get 16V then reduce it to 12V with a resistor in series with the fan.
  8. audioguru2

    UPS

    An old monitor with a cathode ray tube (picture tube) used about 100W or 100VA, not 600VA. A new LCD monitor uses about 20VA.. An adapter for a load of 10W could have a wrong voltage of 1V or 1000V. An adapter rated at 12V/1A might work or might not work since every monitor is different.
  9. audioguru2

    Projects for a newbe

    MS word is used for text, not for schematic diagrams. MS Paint program is good for schematics. I use it all the time to copy and paste parts from other schematics and datasheets.
  10. audioguru2

    0-30V Stabilized Power Supply

    hi sing, I don't know which transformer you have. A 28V transformer is  29.5V without a load. Then its peak voltage is 41.7V which is reduced to 40.3V by the full wave rectifier. You need something  (an LM317HV) to reduce the 40.3V down to 12V for the fan. The voltage limiter will have 40.3V -...
  11. audioguru2

    0-30V Stabilized Power Supply

    The U1 opamp has a max output current of about 20mA. A fan draws a lot more current. The 11.2V from U1 can drive a power darlington transistor which will have an output of about 9.4VDC. The power darlington will get very hot and will also need a pretty big heatsink. Or you can use an LM317HV...
  12. audioguru2

    0-30V Stabilized Power Supply

    What is a "cooler"? Is it a heatsink? Why? U1 opamp operates with a load current of 5.6mA in the new version and dissipates only 300mW so it is just a little warm.  I do not know what you are asking.
  13. audioguru2

    0-30V Stabilized Power Supply

    we had a thread about fixing this power supply project that was about 155 pages long but it got deleted when this site crashed. The same questions over and over and over and ....
  14. audioguru2

    0-30V Stabilized Power Supply

    This power supply circuit is very simple. I fixed it so that it meets its spec's and is reliable. I use LTspice IV software for analysing audio amplifiers but have never used it on this power supply. I never built this power supply.
  15. audioguru2

    0-30V Stabilized Power Supply

    The output voltage of U1 should be +11.2V. The slider of the voltage setting pot should go from 0V to +11.2V. U2 and the output transistors form an amplifier with a voltage gain of (56k/27k) + 1= 3.074 so the 11.2V input to U2 creates 34.4V at the output if the unregulated supply voltage is high...
  16. audioguru2

    0-30V Stabilized Power Supply

    The LED lights and current regulation happens when U3 detects the voltage across R7 caused by load current is more than the voltage set at the current regulation pot. 3A in 0.47 ohms causes a voltage of 1.41V. The slider of the current setting pot should go from almost 0V to +1.41V.
  17. audioguru2

    0-30V Stabilized Power Supply

  18. audioguru2

    0-30V Stabilized Power Supply

    Do you mean that the problem where the output voltage was always -0.5V is fixed because a 741 opamp was burned? I don't know what you are asking. It is normal for the output voltage of U3 to be +30V when it is not regulating the current. The output voltage of U2 is about 1.5V higher than the...
  19. audioguru2

    audio amplifiers

    Most of the amplifiers on Rod Elliot's site use class-AB and a few use class-A. The class-A amplifiers waste a lot of power making heat.
  20. audioguru2

    0-30V Stabilized Power Supply

    The original project used a 24v/3A transformer. Without a load on the project the transformer will probably be 25v and have a peak voltage of 35.4V then the rectifier bridge will reduce it to 34v which will be the positive unregulated supply. since opamps U2 and u3 also use the negative -5.6V...
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