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  1. audioguru2

    RCA audio Line voltage?

    Hi Dave, There isn't a standard because how loud is loud? One manufacturer doesn't care about working with something from another manufacturer. Most music sources for home stereo equipment have a line output of 100mV to 300mV RMS for the loudest. That is 283mV p-p to 848mV p-p. Car amplifiers...
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Hana, Welcome to our forum. ;D R7 must be about 0.47 ohms. Use two 1 ohm resistors in parallel if you want. Good. Q4 should be two power transistors in parallel. Q3 is a small transistor.
  3. audioguru2

    Audioguru FM Tx

    Hi Walid, The jFET in an electret mic makes a pretty good constant current sink but it isn't extremely high impedance. I measured my mic with 10k as R1 and their total resistance was 3.33k ohms. Therefore the mic alone is 5k ohms. The preamp transistor Q1 in that transmitter has a total input...
  4. audioguru2

    Doubling 7805 regulator current is effective?

    Switching regulators are nice and cool. But they are very complicated.
  5. audioguru2

    Led display Digital Voltmeter question

    I don't see a calibration adjustment to make the meter read 1.999V max on its lowest range. The datasheet for the IC shows it with a 199.9mV max lowest range. For the lowest range to be 1.999V max, then R3 should be disconnected. For 19.99V max, R3 should be 111,111.11 ohms. For 199.9V max, R3...
  6. audioguru2

    5 second delay System

    No I don't know what you mean. Nobody is there but stereo sound is playing for the mice or flies to hear. But you don't want them to hear the sound live, you want them to hear the sound with a delay. You don't say why you have stereo sound playing for nobody to hear it. You didn't say why you...
  7. audioguru2

    5 second delay System

    Hi Clue, Your computer can do it but it might need a second sound card: 1) Inputs go to your sound card that digitizes the signals. 2) Store the digitized signal in RAM. 3) A second sound card converts it back to stereo audio and you play it with a 5 seconds delay. One cassette recorder then 5...
  8. audioguru2

    Doubling 7805 regulator current is effective?

    Hi Wellington, If you parallal three 7805 regulators, they each will have a slightly different output voltage, so the one with the highest voltage will take the entire load then current-limit and its voltage will drop down to where the next lowest voltage regulator will begin to work, etc. Lousy...
  9. audioguru2

    Led display Digital Voltmeter question

    The list for R3 in the project is wrong and is backwards: 1) How can the meter measure 0V to 2V when R3 is zero ohms? The input would be shorted. 2) You have R3 as 1.2k and the project shows 1M for R4. So with 12V into the 1M to 1.2k voltage divider, the meter's input gets only 0.01428V.
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Grs, The opamps have very high resistance FET inputs so yes you can use 100k pots: 1) Their wiring should be shielded so it doesn't pickup mains hum radiated from the transformer or the mains cord. 2) Multiply the values of R17 and R18 by 10.
  11. audioguru2

    Audioguru FM Tx

    Correct. The drain of a jFET is a high impedance current sink like the collector of a transistor. But the signal modulates its constant current. The constant current becomes only a little higher when a lower resistance of R1 increases the voltage at the drain of the jFET. No. The signal...
  12. audioguru2

    Audioguru FM Tx

    Hi Walid, An electret mic should have about 0.5mA through it. For its FET transistor to have some gain the load/powering resistance should be as high as possible but still allow a few volts across the mic. So with a 9V supply, a 0.5mA current and about 5V across the mic the powering resistor...
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Rufinus, Check the values of R17, R18, R19, R20, R21 and P2. Check that C8 and Q3 aren't shorted. Swap U3 with another opamp. What is the voltage of the negative supply?
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Rufinus, U3 controls the current regulation. If the two end terminals of the current adjustment pot P2 are reversed, then you will have low current when it is turned up and high current with the LED off when the pot is turned down.
  15. audioguru2

    Transfer funtion

    Hi Baok, Did you look at the graphs of a diode's transfer function in its datasheet? The 1N4148 has graphs with extremely low and medium currents where the transfer functions are perfectly straight lines. I attach the graph where its current is pretty high for such a small diode. The datasheet...
  16. audioguru2

    Problems with my 555 circuit

    The max current rating for an ordinary LED is only 30mA. The output current of an ordinary (not the Cmos one) 555 is more than 200mA. Without something to limit the current then the LED or 555 will be damaged. Maybe you are lucky that your battery cannot supply enough current to cause damage by...
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Grs, Welcome to our forum. ;D The 24VAC transformer in this project has a voltage too low for the circuit to have a regulated output of 30VDC at 3A. It will probably be about 25VDC max. Then if you turn up the voltage adjustment pot further the output will have ripple. An ordinary and cheap...
  18. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    Hi Sarma, I know about remote voltage sensing at the load so that the feedback causes a power supply to produce an accurate voltage at the load without the voltage drop of the connecting wires. This project is smart because it has the current sensing resistor R7 outside the voltage sensing...
  19. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    Hi Sarma, I have seen too many circuits posted that are built on a breadboard with thin long wires all over the place. Some are clipped together with intermittent alligator clips. They cannot work properly.
  20. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    Hi Roomi, Datasheetarchive.com doesn't list the darlington. It would overheat by itself so at least two are needed. The driver transistor and a couple of resistors might not be needed.
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