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  1. audioguru2

    ATX power supply

    Hi Vedran, The FryGuy has an interesting way to get lots of power. I don't like to short together the outputs of power supplies without resistor or diode isolation. They won't have exactly the same output voltage so the higher one will "hog" the load current. I also don't like to short the...
  2. audioguru2

    big ear, fm transmitter.

    Hi Steven, Please post Jaycar's schematic for their parabolic mic circuit when you get it.
  3. audioguru2

    ATX power supply

    Hi Vedran, The 230V/115V selector might not be an expensive switch but is probably just a wire with a jack that plugs onto a pin. The pins should be marked. You are correct. The schematic shows a separate 5V supply that powers PS-ON, which should measure about 4V. It is powered from the...
  4. audioguru2

    ATX power supply

    Hi Ante, Do you think it is C4 on the schematic that has blown? I have never seen a ceramic cap marked 221J before, even a little 220pF cap would be marked 221Z5U or 221COG. A 220nF ceramic cap is usually marked 0.022. I think it is a 220V 5% MOV, which would be Z2 on the schematic. Maybe...
  5. audioguru2

    square wave to sine wave converter

    Hi Kevin, The circuit that you posted is a common Wien Bridge Oscillator, that produces a sine-wave by using positive feedback around the 1st opamp by the bandpass-filter of the equal RC networks (the Wien Bridge). The 1st opamp's negative feedback resistors of R3, R4 and the FET give it a gain...
  6. audioguru2

    big ear, fm transmitter.

    Hi Steven, I hope you don't have to make a complicated digital frequency synthesized transmitter just to match today's digital radios.
  7. audioguru2

    big ear, fm transmitter.

    Hi Steven, A digital radio relies on the excellent carrier frequency stability and accuracy of radio stations. Your transmitter's frequency probably drifts due to temperature and supply voltage changes so its signal drops-out. Use an analog radio with AFC.
  8. audioguru2

    Led Display Digital voltmeter problem with 200mv scale

    Maxim-ic's improved (at no extra cost) IC guarantees a 000.0V reading with 0V input and its accuracy is guaranteed to be plus or minus 1 count, which is 0.1mV. It is actually better than that but can't display it. Its noise and temperature drift are guaranteed to be 15uV or less, but most IC's...
  9. audioguru2

    Led Display Digital voltmeter problem with 200mv scale

    Hi Karter, Welcome to our forum. Did you use Maxim-ic's improved IC or Intersil's old one? Did you use metal-film resistors that are very stable, or ordinary carbon-composition or carbon-film ones that are unstable?
  10. audioguru2

    heavy duty batteries

    Hi M. Junior Evil, "Heavy Duty" battery cells are lousy and use old carbon-zinc technology. They have a very low capacity and current driving ability and self-discharge (then leak) in about 1 year even if not used. Alkaline battery cells are much better, especially at high currents. The ones I...
  11. audioguru2

    Pages take forever to load?

    Hi Mixos, Thanks for fixing the PHP errors, you are doing a fine job. ;D Before when I clicked on this site or navigating within, my browser would say, "Web-site found, waiting for reply", and a long wait. But it doesn't do that anymore, instead lately it says, "Connecting to http.....", and a...
  12. audioguru2

    3V LED Chaser project

    Hi Andrew, A transistor multivibrator usually works fine with a supply voltage of 6V or less. Above 6V the transistors would need diodes in series with the emitters to protect their b-e junctions from reverse overvoltage breakdown. But the output high-going switching time of a transistor...
  13. audioguru2

    Pages take forever to load?

    The PHP errors are fixed, but now navigating around this site is very slow.
  14. audioguru2

    Beginers OPAMP question

    Hi Kevin, Please forget about collector resistors, beta and "emitter elements" when discussing opamps. An inverting opamp circuit simply consists of an opamp, a feedback resistor and an input resistor. The charactristics of an opamp are that it has an enormous voltage gain, differential inputs...
  15. audioguru2

    Electronic Stethoscope 2

    Hi Steven, I am sorry to say the circuit won't work the way you changed it: 1) You have the volume control connected to pin 7 of the TL072 which is the output of its 2nd opamp, but that opamp's input at pin 5 is not connected to anything. For your "big ear", you don't need the low-pass filter...
  16. audioguru2

    Electronic Stethoscope 2

    Thanks Steven (Sparky), I look forward to reading about and seeing pics of your big sparks!
  17. audioguru2

    Electronic Stethoscope 2

    Hi Steven, A few people have built it and reported in these posts that it is successful. This one doesn't work because it has wires shorting or in the wrong place.
  18. audioguru2

    Electronic Stethoscope 2

    Hi Manny, Welcome to our forum. I am sorry that your 2nd project didn't work. We can troubleshoot it with voltage measurements, etc. if you wish.
  19. audioguru2

    3V LED Chaser project

    Hi Guys, I knew it would happen. When my daughter saw my "6V" Ultra-bright Blue LED Chaser, she liked it and took it to match the red 3V LED Chaser that I gave her a while ago. Her friends want the red ones and will probably want the blue ones too. Luckily, my local electronic surplus parts...
  20. audioguru2

    Problems with headphones... static?

    Hi Steven, I typed this text, highlighted it then clicked the Marquee button. Now I typed this text, highlighted it then clicked the Marquee button twice, to see if it would scroll twice as fast. ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D...
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