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  1. audioguru2

    FM WAVE PROPAGATION

    I never heard of a capacitor that has its polarity marked backwards, but I guess anything is possible.
  2. audioguru2

    fm tranismiter

    Hi Mp, Thanks, I completely forgot about that one. I have an NE572 stereo one in my stock that I could try. Philips' "Compandor Cookbook" is full of applications for them: http://www.semiconductors.philips.com/acrobat/applicationnotes/AN176.pdf
  3. audioguru2

    fm tranismiter

    Hi Kevin, My FM transmitter circuit badly overmodulates when a loud sound or talker is too close to its microphone. I made its preamp gain high enough to pickup conversations about 2m away. I built the original circuit of a defective transmitter to see everything that was wrong with it and when...
  4. audioguru2

    0-30 Vdc Stabilized Power Supply

    That's what I used, a 25W one is much smaller than that.
  5. audioguru2

    fm tranismiter

    Sorry, Sasi. I don't have the circuit of my old cable TV amplifier anymore.  :'(
  6. audioguru2

    SUPRA Model STV-2128MS Schematic

    Hi Rhonn, Do you guys have Pontiac TVs? He, he. That's what I drive. Is Daewoo still in business? When they nearly went bankrupt I think General Motors bought them. GM imports some new little Korean cars this year but I don't know if Daewoo or some other company makes them.
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Thomas, If you can't get a powerful 0.47 ohm resistor, use a 0.39 ohm one and change the other parts around the current-set pot to match. I bought a 25W aluminum-clad resistor and was amazed at its tiny size. I thought it would smoke for sure since at what extremely high temp does nichrome...
  8. audioguru2

    SUPRA Model STV-2128MS Schematic

    A SUPRA is a Toyota car!
  9. audioguru2

    FM WAVE PROPAGATION

    Exploding tantalum capacitors are worse than electrolytics. Molten metal spits all over. Ouch!  ;D
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Blacque, To use a range switch, you use a fixed main resistor and in parallel with it a high-value pot and a bunch of series connected scaled resistors in series. The switch shorts the resistors one at a time to change the range. Use a make-before-break switch to keep the current from...
  11. audioguru2

    OPTOCOUPLERS

    Hi Prateek, Optocouplers provide electrical isolation: 1) You connect the output of your computer directly to the gate of a Triac to turn on and off a mains-powered lamp. But the ground wire of the lamp and the Triac are accidently connected to 220VAC instead of to the neutral wire of the mains...
  12. audioguru2

    Designing feedback amplifier

    Hi Yousef, NOT TRUE! The single-supply opamp has its input biased at half the supply voltage so that its input and output can swing equally both positive and negative with respect to half of the supply voltage. The opamp's input and output are capacitor-coupled to allow this. The "half supply"...
  13. audioguru2

    fm tranismiter

    Hi Sasi, If you could find a cheap cable TV amplifier that isn't overloaded all the time like most of them, an antenna could be connected to its output. In the olden days, my cable had about 78 channels and the cable company gave just barely enough signal for one TV set. When you added a...
  14. audioguru2

    fm tranismiter

    Yeah, You got the correct IC, I got the wrong one! Those guys at Maxim must have tin ears. The high-value cap at pin 3 will cut high audio frequencies, and the circuit doesn't have pre-emphasis capacitors across R3 and R4. An FM radio receiving a transmission from that transmitter will probably...
  15. audioguru2

    fm tranismiter

    Hi Sasi, That 60W RF amp in our projects section doesn't even say what frequency it amplifies. Since it mentions QRP which is for ham or amateur radio, and it has a very high-value tuning cap and a coil with a core, it is probably for short-wave, certainly not for the FM broadcast band.  ...
  16. audioguru2

    OPTOCOUPLERS

    The coupling of a 4N25 optocoupler and many others are guaranteed to be at least 100%, so it has pretty good "efficiency". Its output switches off in 2us, so it can have its emitter (LED) modulated with any audio frequency and low-speed data as signals.
  17. audioguru2

    Shut off timer

    Hi Falsh, Welcome to our forum. I would just take a cheap LED alarm clock and replace its beeper with a small audio isolation transformer. Then I would rectify and filter the beeping pulses into a DC voltage that I would feed to a Triac that switches the electrical outlet for the lamp to the...
  18. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Blacque, Good idea, but I would just use an ordinary marked pot and a range switch.
  19. audioguru2

    AAA Battery Charger

    Hi Smart, The battery cell capacity is 250mA/hrs. The recommended charge is 7 hrs at 50mA, which is 350ma/hrs. 350/250 = 140%. You charge for 40 percent more than its capacity. The air inside the battery compartment won't heat like the battery unless there is very little air and it is sealed...
  20. audioguru2

    fm tranismiter

    Hi Alun, The old CA3140 is too noisy for a high gain microphone preamp. There are lots of different low-noise audio opamps you could use.
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