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  1. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Aergotic, I always design circuits for "worst case" conditions because you don't know what the current gain of your transistors will be, just a range of current gain. If your transistors have the lowest minimum guaranteed gain, you still want the design to work, and reliably. The project's...
  2. audioguru2

    Additional Information

    Hi Nab, 1) The absolute maximum input voltage of the counter is its supply voltage. If you power the 741 opamp from +15V then its output voltage will swing up to about +14V and feed about +13.4V through D1 to pin 14 of the counter, damaging it. 2) The project is designed for an opamp like the...
  3. audioguru2

    4W FM Tx

    Hi Knownothing, I guess you built this project: http://www.electronics-lab.com/projects/rf/001/index.html Sure, it will have temperature problems if its antenna is the wrong  impedance or length, or if the whole circuit isn't "aligned" (tuned) properly. Use its minimum supply voltage of 12V and...
  4. audioguru2

    Our Site Doesn't Open

    Hi Mixos, Wow, your site is now really fast and has lots of improvements. Thanks a lot!  ;D ;D
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi  Blacque, Sure, make your own darlington with a couple of BC557's. Make certain the 2nd one turns-off with a 100K resistor from its base (and the emitter of the 1st one) to its emitter (the positive supply). Use a 1M resistor from the base of the 1st one to the positive supply, and a 470K...
  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Blacque, You are correct, the high-value resistors and darlington transistor are needed to keep the existing LED dimmed. Our vision's response to brightness is logarithmic so even a tiny current in an LED is obvious. What's wrong with PNP circuits? Can't you read upside down?  ;D ;D
  7. audioguru2

    AAA Battery Charger

    Hi Smart, Sorry, I was mistaken when I said that. I thought the diode was with the opposite polarity. The 555 charges the capacitor through the 55K resistor in series with the diode for about 550ms. The cap is discharged by the 19K resistor for 209ms.  I don't know how you figured a discharge...
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Blacque, Sure, use the existing spare TL081 to drive the current meter. You could drop-down the positive supply voltage to 5-10V (it doesn't need to be accurate) with a 2-resistors voltage divider, and use the 5.6V negative supply. A bypass cap at the positive terminal of the TL081 would be...
  9. audioguru2

    fm tranismiter

    Hi Sasi, Oh! It is my circuit. When I saw a great big round electrolytic capacitor on your pcb for C4, I thought it would bypass R5 completely at all audio frequencies, causing high gain and distortion, without pre-emphasis. Adding a through hole above the "8" will fix the pcb by allowing for a...
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Blacque, Welcome to our forum. You have some good meters and a good idea to measure current. An external current meter will have a voltage drop and ruin the good voltage regulation of this project. R7 is outside the feedback loop so has no effect on output voltage. Sure, amplify the 1.41V up...
  11. audioguru2

    25 Khz oscillator

    Hi Kevin, Good, you got your transistor doing something, but the whole circuit still has problems: 1) Where are your phase-shifting filters? You have two very low-impedance (at 25KHz) caps in series without any phaseshift. 2) What about the opamp output overloading problem caused by the 64 ohm...
  12. audioguru2

    Our Site Doesn't Open

    Hey, I finally got in! I don't believe that it actually allowed me in. Let's see if I can surf.
  13. audioguru2

    fm tranismiter

    Hi Sasi, It would have much more output power and melt the little 2N3904 at the output, and the 2N3866A would also get hot and help drain the battery quicker. Using either a 2N3866A or a Mosfet would damp the output tuned circuit so they would just cause a very high supply current. Maybe if the...
  14. audioguru2

    25 Khz oscillator

    Kevin, I don't see how it can be an oscillator, operate as high as 25KHz nor have a sine-wave output. The capacitive reactance of its "104" capacitor (0.1uF?) is only 64 ohms at 25KHz so would seriously overload the output of the opamp if it had an output, and the 10M resistor across it is so...
  15. audioguru2

    fm tranismiter

    Hi Sasi, You have a nice pcb design. ;D Which schematic? It appears to have a very high gain distorted preamp without any negative feedback or pre-emphasis. ???
  16. audioguru2

    Our Site Doesn't Open

    Our new server didn't last very long did it? :'( :'( I wonder how long it will last this time. ???
  17. audioguru2

    Designing feedback amplifier

    The voltages around an opamp are not imaginary, they are tried and proven!
  18. audioguru2

    fm tranismiter

    Sometimes I get excited which makes me speak loudly and get too close to the microphone! ;D
  19. audioguru2

    Designing feedback amplifier

    Kevin, What are you talking about? Forget about PN junctions, new Cmos opamps don't even have any PN junctions. Besides, an opamp is an extremely high-gain complete amplifier, not just a transistor. Since its gain is almost infinite, negative feedback keeps its inputs voltages nearly the same...
  20. audioguru2

    Designing feedback amplifier

    Hi Yousef, No, no, no, no! Opamps don't need two power supplies. Single supply opamp circuits work exactly the same as dual supply circuits:
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