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  1. Hero999

    74188, 74287, 74288, 74387

    It is annoying when that happens. I often ask another question and only before I bother to do something.if they reply. Never mind the datahseets are now here for anyone else that wants them, until the forum crashes again and we loose all the posts.
  2. Hero999

    schematic search

    There are several ways of doing it. File splitter is good because the files can be all joined back together using a batch file or the copy command - no additional software is required for the recipient. UNIX (Linux, BSD, Mac OS X etc.) has a split command that comes with the OS and the files...
  3. Hero999

    Response to: A power source for simple LED projects

    If you're answering someone's question, you should respond to the appropriate thread, not create a new one, otherwise we have no idea what you're talking about.
  4. Hero999

    schematic search

    Why can't you simply split the file into three parts or host it somewhere else?
  5. Hero999

    schematic search

    1) Don't derail someone else's thread, create your own. 2) Use good English - you obviously need to work at this. 3) Give as much information about your question as you can. 4) Bear in mind that we won't do all the work for you, make the effort to learn yourself and help us to help you.
  6. Hero999

    Virus warning

    Hang on, the warning indicates that the virus is on your Documents and Settings folder on your computer so it might not be the site. I suggest you scan your hard drive for viruses and see if that helps.
  7. Hero999

    Virus warning

    It looks like it's the advertising Java script based software used to create all those nasty pop-up links. It might be a virus or it could be a false alarm. Either way, if it really bothers you, get ad-blocking software or disable scripting for this site and you should no longer receive this...
  8. Hero999

    Water level detections system

    It depends on what you want to do, if you just want to turn a pump off when the tank is full you could just use a float switch but if you want to gauge the level of the fluid in the tank something more complicated is required.
  9. Hero999

    JFET Mic Pre Advise Please

    Good, the voltages and currents are within the expected ranges. Q1's drain current is 2.2mA. a bit higher than I predicted but it's reasonable. The drain voltage is 17.3V which is roughly equal to 36-2.21*8.5 and is perfect as it's nearly dead on half the supply voltage. This means that your...
  10. Hero999

    JFET Mic Pre Advise Please

    Where did you get 0.06 from? I assume, it's the value of R3. You haven't included the voltage between Q1's drain and source in your calculation. The current through Q1 is dependant on the gate-source voltage, the lower the gate voltage (relative to the source) the lower the current. The value...
  11. Hero999

    JFET Mic Pre Advise Please

    The drain should ideally be biased at half the supply voltage to allow as greater swing as possible. In practise it doesn't have to be exact, it just needs to be far enough from either of the supply rails to avoid clipping. For example if the drain is biased at 2V, the negative cycles will clip...
  12. Hero999

    Parametric Interaction

    I don't think it's practical to use ultrasonics unless it's narrow bandwidth i.e. voice only or  you use digital compression. How many ultrasonic transducers can you buy that have a the 20kHz bandwidth required for single side-band AM?  Most transducers have a sharp resonant peak. That's a...
  13. Hero999

    New Spam

    Closing the high voltage section might increase spam in other areas. I think the same is also probably Sell/Buy electronics - Job offer/requests section.
  14. Hero999

    Parametric Interaction

    How about posting a link so we know what you're talking about? I've done a quick Google and couldn't find it. I'm not doubting that it exists, I've seen it before, I'm just not going to click on ever link on every page of results to find it.
  15. Hero999

    JFET Mic Pre Advise Please

    Using a Darlington is good because the gain is higher, (normally 10,000 without looking at the datasheet) meaning the input impedance will be higher. Why have you insisted on a non-standard value  (8k5 isn't even an E192 value) for R1, is it merely because you have it in stock? As mentioned...
  16. Hero999

    Parametric Interaction

    The details of how to do it are probably a trade secret so I doubt you'll be able to find a schematic anywhere.
  17. Hero999

    JFET Mic Pre Advise Please

    I thought it was supposed to be a pre-amplifier? The bottom transistor is set up as a constant current sink, albeit not a very good one. The trouble is the current will be 63mA which is far too high for a pre-amplfier and will melt a small signal transistor. It might not be this bad, he did...
  18. Hero999

    JFET Mic Pre Advise Please

    Why would you need to swap it round? I don't think you understood me: you only need to clamp the negative pulses, the JFET's gate behaves like a forward biased diode when the gate voltage is higher than the source, which will clamp any high voltage positive spikes. The output impedance needs to...
  19. Hero999

    JFET Mic Pre Advise Please

    What does the xlr grounding pin do? If 49.9R is recommended then use it. What load is the pre-amplifier driving? It needs to have a significantly higher impedance than 4.02k, as a general rule of thumb, it should be at least ten times higher otherwise the gain will be reduced significantly...
  20. Hero999

    JFET Mic Pre Advise Please

    Disclaimer I'm no expert with discrete JFET amplfiiers. Just a few things I've noticed about your circuit: The gates of both transistors are biased at 0V which will bias them too far on. Ideally Vgs should be kept negative and should never exceed the 0.6V turn on voltage which will probably...
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