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  1. audioguru2

    LM78XX & LM79XX questions

    No Kevin, The datasheets say that the regulator's output capacitor is used to improve its transient response. 1) If a load is suddenly applied to a regulator, its output voltage would drop suddenly because its high-gain amplifier is slow to react. The output capacitor supplies current to the...
  2. audioguru2

    Question from a student about amps

    We use Decibels because they measure a change in level logarithmically, like our hearing. Therefore the levels don't have many digits: +120dB is a voltage (level) gain of 1,000,000. -120dB is a loss to 0.000001.
  3. audioguru2

    LM78XX & LM79XX questions

    Hi Autir, This topic is never dead!  ;D The power transformer isolates your LM78xx and LM79xx circuit from the ground of your mains power socket. Same for a rectifier bridge. With the isolating transformer, the circuits have their ground terminal grounded if you wire the circuit ground to the...
  4. audioguru2

    Want to use LED Dot Matrix Board

    Instead of having a separate wire for each LED which would require 65 pins and 64 transistors to drive the LEDs, they are connected in common so that they can be multiplexed. Search Google for one of many LED Oscilloscope circuits.
  5. audioguru2

    4W FM Transmitter

    The J-pole is a funny looking antenna. Why not a high-gain Yagi?
  6. audioguru2

    4W FM Transmitter

    Hi Sasi, I don't know what is a "J-pole" antenna, and I am sorry I can't calculate range. This much RF power is very illegal. Many years ago I installed doctors' radio-paging systems in hospitals. Before installing "leaky cables" on lower floors and reducing the RF power, I needed an RF power...
  7. audioguru2

    detector prototype

    Hi Badai, 1) The project specifies using a microwave transistor and diode, you are using a general purpose 250MHz transistor and high frequency diode. 2) The DC gain of opamp A1 in the project is usually defined as the ratio of resistors R6 (1M) divided by R12 (220) if the circuit is driven from...
  8. audioguru2

    detector prototype

    Hi Badai, I couldn't find out anything about your AA215 diode. Your 2N2222 transistor will have gain up to at least about 60MHz, no gain at about 180MHz and lose more signal at higher frequencies. The VCO is an audio oscillator with no output at a very low detected signal level and a higher...
  9. audioguru2

    Electronic Stethoscope

    Here's another European little amp IC: http://www.fieros.de/philips/tba820m.pdf
  10. audioguru2

    Piggy-backed PC power supplies?

    Hi Alun, You will be causing a conflict with the two supplies: #1 PS senses that the voltage is too high but it is coming from the other PS, so #1 PS lowers its output voltage more and more. Then the other PS supplies the entire load current. The supplies must have exactly the same output...
  11. audioguru2

    OPTOCOUPLERS

    Can you trust that all your electrical outlets or the lamp with a triac are wired correctly? If one is wired backwards then its ground is really live. If it is connected to your computer then many Amps will flow through the connection until the fuse or breaker blows. Or maybe your grounded...
  12. audioguru2

    741 op amp

    An opamp desn't need a ground pin.
  13. audioguru2

    AM to FM convertor

    Yeah, your screwdriver adds 10pF to 20pF to the whole circuit. File a piece of hard plastic into the shape of a screwdriver shaft and glue it into the end of an empty plastic pen. I use a plastic tool for trimmers that has a plastic cup at the end that fits over the trimmer's screw. The cup has...
  14. audioguru2

    AM to FM convertor

    Hi Andbor, The FM radio makes a noise so maybe the project's tuning is close. Try tuning the project's trimmer cap slowly with a non-metallic tool, with the FM radio at each end of the dial.
  15. audioguru2

    Need help with a TV transmitter project.

    Hi Dazza, The blue things are probably inductors and should have an "L" number beside them. Their two dots probably indicate their value in uH. The problem is which way is up (or down) so that it might be brown and green which would be 15, or 51.
  16. audioguru2

    741 op amp

    The 8-pin package is standard, they have never had a 7-pin package. Many opamp circuits use the negative supply as ground.
  17. audioguru2

    OPTOCOUPLERS

    An optocoupler can "couple" a DC current (a transformer can't) as well as an AC current.
  18. audioguru2

    AM to FM convertor

    Hi Andbor, Aw, c'mon make the darn thingy and let us know what it does. Maybe it will work fine. It only has a few parts! I don't know what a suggestment or an MK484 is since I hate AM radio. There are lots of simple FM transmitter circuits that can be found here but our "Search Site" button is...
  19. audioguru2

    Electronic Stethoscope

    Hi Dazza, It is wonderful to hear that you are going to be a daddy!  :o  ;D The LM386 1/2W amp has been very popular over here. It is used in nearly every small radio or tape player, and wireless baby monitor that I have ever seen. I don't know what brands you can buy down under, but Philips...
  20. audioguru2

    AM to FM convertor

    Hi Andbor, We know exactly what a simple AM receiver will pickup and how a simple FM transmitter works. We don't see how the AM to FM Converter can possibly do what its author says it will do, "The capacitor C1 can be varied to receive different AM stations". I'm not going to build the thing to...
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