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  1. audioguru2

    Design of PC Speaker

    Hi Izach, A 1uF capacitor is much too low a value to feed an 8 ohm tweeter. It would cut frequencies below 20,000Hz. A 4.7uF capacitor would have a 4255Hz cutoff frequency.
  2. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, Metalized plastic film capacitors are self-healing. The metal film on the platic film is so thin that arcs caused by over-voltage just vapourises the metal where an arc occurs. ;D
  3. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, Thanks for doing an autopsy on your photo-flash capacitors that died. ;D It is interresting that they show signs of too much discharge current. They probably have a very low internal resistance and therefore their current must have been high enough when you shorted them that it...
  4. audioguru2

    How do you find the size of the cap if no label?

    I wouldn't re-use a cap without a label because you won't know its voltage rating. If it is defective and needs replacement then testing it will probably give a false reading.
  5. audioguru2

    5 minute timer where a mechanical motion is required

    Not in the Arctic in winter! ;D ;D Goooooooo? A brick can be used as a float for awhile.
  6. audioguru2

    Using multiple monitors - Help?

    Hi Stuee, My video distribution amplifier fed 6 RGB monitors. It could feed hundreds of monitors. I use Motorola triple video amplifier IC's which are obsolete now. Most semiconductor manufacturers make video or VGA distribution amplifier IC's and they are simple to use. ;D
  7. audioguru2

    Using multiple monitors - Help?

    Hi Stuee, I think the circuit is too simple to drive monitors. Its emitter-followers don't pull-up the signal, its 100 ohm resistors do but with signal loss. I built video distribution amplifiers for video conferencing systems. I used IC's developed for the application that had push-pull...
  8. audioguru2

    5 minute timer where a mechanical motion is required

    Hi Iceman, Adding salt to the water won't allow it to conduct enough elecricity to light-up low voltage lightbulbs. The darlington transistor that was shown will work well as a sensor for water that doesn't have salt added, but might not work if the water is pure or distilled.
  9. audioguru2

    Thermistor with op-amp

    If the pot was in series with the thermister, instead of being as part of the reference voltage, if it was adjusted to a low resistance then the thermistor would heat-up. It is best to keep the pot away from the thermistor. ;D
  10. audioguru2

    Thermistor with op-amp

    I think it allows the 68k resistor to reduce the current through the thermistor so it doesn't heat-up. Changing the reference voltage for the opamp with a variable voltage divider from the supply still allows the temperature threshold to be adjusted or to allow for differences between different...
  11. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Alun, A voltage full-wave voltage doubler for a 3A output would need 3 (or 4?) huge capacitors and powerful rectifiers. Another low-current doubler might be needed for the negative supply but instead a few resistors can have their values reduced.
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    Thanks, Mongseng. ;D It is best to keep with the modified project. Are you going to make it for 3A or 5A? ???
  13. audioguru2

    Outdoor Light Status Indicator

    Hi Ante, Gary doesn't say which LED he used. I have seen the tiny size of the bonding wire inside my clear LEDs and the case magnifies it. 10A! I wouldn't even put that much current through the dinky little SCR he used. Years ago I used that SCR to drive 40mA relays. ;D
  14. audioguru2

    Thermistor with op-amp

    Kevin, The opamp's output is saturated most of the time so it doesn't have any gain. The output doesn't change until the thermistor's voltage divider provides a voltage that reaches the Schmitt trigger threshold of the opamp. Then the opamp switches as fast as it can due to positive feedback and...
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    It will take me a few hours or days to redesign this project for your low-voltage transformer. Just about every resistor wil need to be analysed. :'( :'( :'(
  16. audioguru2

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

    Hi Thomas, A BZX79C5V6 zener diode is fairly temperature stable but you can use a TL431 reference if you want. You have a better way[/b[ to make the modified project cost less. ;D The output voltage of U1 is only 11.2V so will work fine with a cheap 18V/0.5W zener diode across it and a 1.8k/1W...
  17. audioguru2

    high voltage photo flash capacitor charger

  18. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Monseng, If a few resistor values are changed in the circuit then the 16V/5A transformer can be used and the modified project will deliver 15V at 3.5A. ;D
  19. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, Are you using a blinking LED that has a built-in blinking circuit and current-limiting ? What supply voltage are you using for the transistor and LED? What high voltage does the photoflash capacitor charge up to? Could you post a schematic of the capacitor charge voltage indicator...
  20. audioguru2

    Switching power supply

    Hi Ante, I always design circuits using manufacturers' guaranteed minimum specs and everything works fine. ;D I also still have my very first psu that has a BDY38 (I have its 1968 datasheet) silicon transistor replacing its original germanium AD149. I can hardly read the label on it since it is...
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