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  1. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, Your 555 timer circuit looks OK but I don't see a local supply bypass cap that most electronic circuits need, and as described in the 555's datasheet. Try adding a 0.1uF ceramic cap and a 10uF electrolytic cap near the 555 from its supply pin to its ground. 1) What is the timer's...
  2. audioguru2

    Reduce output Voltage of Power Supply

    Hi Robert, I just bought a bunch of 5V/2A wall-wart switching supplies for only 2 bucks each! Their label says, "Output: 3.0-36VDC. Preset for 5V". So they probably have a voltage control inside. Maybe your supplies have a voltage control too. Forget about a resistor voltage divider. Ohm's Law...
  3. audioguru2

    Turn the lamp On & Off gradually...

    Changing the frequency of the AC feeding a lightbulb won't change the brightness one bit. Just like the variable frequency DC motor speed control project that we have that doesn't work. A transistor doesn't work with AC that has ground as a center voltage. You need a huge variable resistor in...
  4. audioguru2

    AM RECIEVER

    The IF frequency of an AM radio is nearly 100 times higher than the highest modulation frequency, so amplitude variations between any two consecutive cycles of the IF would be neglegible. The loudness is the amount of variation in the entire envelope of the IF carrier, at a very slow audio rate...
  5. audioguru2

    lm741 schematic diagram

    Kevin, You probably won't get zero volts output with the same input voltages. Like most old opamps, the 741 has a high input offset voltage of up to 10mV (and a high input offset current, too). Without feedback, the voltage gain of 100,000 or more will slam the output hard against a power supply...
  6. audioguru2

    Transformer ratings?

    Hi Ante, I know. ;D Kevin started talking about 120VAC and I should have corrected him but I just continued his discussion. He, he. Take an amplifier with Kevin's 120V/50VCT transformer to The Philippines and plug it into 230VAC. Even in far away Sweden you'll hear the big Ka-Boom! 8) ;D
  7. audioguru2

    AM RECIEVER

    No Kevin, I don't know why you don't believe me, but this is how AM modulation works: ) A radical change in the amplitude of an AM modulated carrier indicates a change in loudness (or volume) of its modulation and occurs in its demodulated output. 2) If you AM modulate a carrier with a high...
  8. audioguru2

    AM demodulator diode

    Hi Kevin, As I pointed-out in you other post about AM demodulation, a modulated AM carrier has equal positive-going parts and negative ones. Therefore the modulation cancels itself. Rectification of the carrier will produce an amplitude-changing single-polarity DC voltage that is the modulation...
  9. audioguru2

    AM RECIEVER

    Hi Kevin, If you look at a modulated AM carrier on a 'scope, you will see that the positive-going parts of the modulation equal the negative ones. Therefore if you filter it, the modulation cancels itself and you are left with nothing. If you rectify the modulated carrier with a diode, the...
  10. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, While you are lookin' for the schematic, which IC is it using? I can't read its label.
  11. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, Please answer my questions so that I can help you: 1) On your timer circuit, what does the "start" button connect to. The timer circuit that you posted doesn't have a start button. 2) When you push the button, does the relay activate?
  12. audioguru2

    AM RECIEVER

    Hi Kevin, Nope. Changing the capacitance load of a signal won't change its frequency. Besides, at low AM radio RF and IF frequencies the few pF of diode capacitance is neglegible. An AM radio's demodulator is simply a rectifier of the 455KHz IF frequency.
  13. audioguru2

    Transformer ratings?

    Hi Kevin, Nope. You forgot about times when the mains is 125V and the transformer is lightly loaded. The capacitors and transistors will go: Ka-Boom! 8) 8) ;D
  14. audioguru2

    Transformer ratings?

    Hi Kevin, We don't always get 120VAC on the mains. At home and at work, the voltage varies from 115V to 125V. You also don't get a voltage out of a transformer that is the same as its rating. Since a transformer's windings have resistance, its output voltage changes with loading, so a 50VAC...
  15. audioguru2

    AM demodulator diode

    Hi Kevin, AM is Amplitude Modulation, which is a fixed carrier (RF) frequency whose amplitude (AC voltage) is changed at an audio rate. 100% modulation occurs when the modulation causes the carrier's amplitude to change from zero for half the audio wave to double on the other half of the audio...
  16. audioguru2

    AM RECIEVER

    Hi Kevin, An AM receiver doesn't have a modulator, it just has a simple AM detector rectifier. Prateek wants to make an AM radio. Hi Prateek, Use a Google search to find an AM radio circuit. You may have a problem finding its coils and transformers.
  17. audioguru2

    Electronic Stethoscope 2

    Hi Steven, What is cir-am002gif? What circuit, what other stage, what other circuit and what other part? What will be complete? Del's burglar alarm? ??? ???
  18. audioguru2

    circuit help

    Hi Steven, My Electronic Stethoscope-2 project is here: http://www.electronics-lab.com/projects/science/019/index.html It uses the LM386 for a headphones/speaker amp, but has reduced gain because it has a separate preamp. circuit. That's correct, to increase the gain of the LM386 by 10 times...
  19. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, Where is your "start" button connected on the timer circuit? That simple timer will activate the relay when power is applied to the circuit until it times-out. Dangerous. A 555 timer circuit won't do that. Your 4001 timer circuit has 4 gates but you are using only one of them. The...
  20. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, Is the 555 relay driver's output voltage activating? If it isn't working, please post its schematic. Charge your battery. Maybe your relay isn't closing because the HV driver circuit 's current is reducing the battery's voltage below the relay's minimum turn-on voltage. Use a 9V relay...
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