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  1. audioguru2

    LM317 circuit doesn't supply enough current (only 20mA)???

    Hi CRE, It doesn't matter if you are a newbie or an oldtimer, all ideas are welcome here, and you've had some good ones. You can't get dangerous with an LM317 because they are "newbie-proof"! 1) Current-limiting. If the output gets shorted or a load goes wrong and tries to draw too much...
  2. audioguru2

    seeking parabolic mic circuit

    Hi Steven, In your LM386 circuit the electret microphone will be more sensitive if you change its supply/load resistor R1 to 10K. The LM386 amp will be a lot more sensitive if you add a 10uF cap between its pins 1 and 8.
  3. audioguru2

    what is noise??

    Hi Eie, If you switch between two inputs that have a different DC voltage, you will hear a "pop" noise, or see a flash on a video screen. Even if you switch between two audio sources that are capacitively-coupled and are grounded by a resistor, if one signal is positive at the moment when you...
  4. audioguru2

    LM317 circuit doesn't supply enough current (only 20mA)???

    Hi CRE, Good point! ;D But even those tiny surface-mount LM317's are good for 500mA, because they have a heatsink tab! I have used little 78xx regulators in a small TO-92 package and they are good for about 100mA. It doesn't make sense to measure a current of only 20mA through a load that...
  5. audioguru2

    "Soft" LED Chaser w/ acceleration?

    Hi CRE, The RGB 3-colour LEDs that I've seen point their colours in different directions. I don't know what type of lense would combine them. Using separate LEDs, my fader has all colours together and I can drive them harder because they remain cooler. I have nearly finished a "6V" ultra-bright...
  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Tom, Welcome to our forum. It is wonderful that your projects work well with outputs up to 25V. Did you connect them as positive and negative supplies? Their output voltages will probably reach a volt or two higher if you replace R15 (1K) with 100 ohms. You can increase the value of C1 to...
  7. audioguru2

    ATX power supply

    Hi Vedran, Do not short the MOV! It is normally open circuit but limits voltage to its rating during high voltage spikes. It never completely conducts like a short. NTCR1 should be easy to find. It is connected in series with the mains neutral wire. Sorry, I don't know what it looks like.
  8. audioguru2

    big ear, fm transmitter.

    But the LM386 IC will be a fairly good battery-powered headphones amp, especially if you use a quiet preamp with it if you don't like its hiss. There are some headphones amp projects on the web called Headbanger and Super-Headbanger. They are battery-powered and use LM386 ICs. They are rated...
  9. audioguru2

    ATX power supply

    Hi Vedran, A MOV is for overvoltage protection from spikes, there is not a capacitor inside, its symbol just looks like a capacitor with a circle around it. The PS should work fine without it until lightning strikes your mains, or until your refrigerator turns off making a voltage spike. A...
  10. audioguru2

    ATX power supply

    Hi Vedran, You wrote "221J", which would make it a 220V 5% MOV. It would safely limit voltage spikes on the 115VAC side of the circuit, which is half the circuit when 230VAC is used. Its diameter determines its power handling ability. ;D Since your PS doesn't work without it, it's too bad that...
  11. audioguru2

    simple tv channel circuit

    Hi Laurent, Have you ever seen a TV's schematic and parts list? It has thousands of special parts that you won't be able to get. A TV's tuner, IF strip and demodulators aren't simple because they need high gain which requires special shielding, and many special tuned circuits that you must align...
  12. audioguru2

    big ear, fm transmitter.

    Hi Steven, It's good that you got your LM386 amp to work. The only thing I recommend for headphones is to add a 1K resistor across the output (where the speaker is connected now) to charge its output cap so if you ever plug the headphones in with the power already turned on, you don't hear a big...
  13. audioguru2

    "Soft" LED Chaser w/ acceleration?

    Hi CRE, My "mood light" circuit smoothly dims the LEDs from almost off to full brightness, not with a linear ramp but logarithmically using a bootstrap circuit. I recently bought some "ultra-bright green" LEDs selected from a catalog and passed over the counter in a sealed bag. They were...
  14. audioguru2

    Question from a student about amps

    Hi Amplifier, Welcome to our forum. Your questions are easily answered: 1) The increase or decrease in logarithmic (to the base of 10) amplitude of a signal or voltage increases or decreases 10 times the actual amount for each doubling of distance along the graph. The amplitude is measured...
  15. audioguru2

    heavy duty batteries

    Hi again Evil, If you put those expensive lithium cells in your son's Game-Boy, then found it a month later under his bed still turned-on and the battery dead, you might cry! ;D ;D I just noticed that Energizer is owned by a razor blade manufacturer. Duracell is owned by the other razor blade...
  16. audioguru2

    ATX power supply

    Hi Vedran, A Metal Oxide Varistor (MOV) is a voltage surge arrestor that quickly limits a voltage to its rating. Its effect on AC voltages is similar to two back-to-back zener diodes. Its small size limits the amount of time it can withstand an overvoltage condition without damage, so it is used...
  17. audioguru2

    "Soft" LED Chaser w/ acceleration?

    Hi CRE, It makes a big difference which IC you use. You need to select the IC to fit your application and supply voltage. An ordinary CD4xxx IC operates with a supply voltage from 3V to 18V but very poorly below about 5V and can use signals up to around 2MHz. A high-speed 74HCxx IC operates with...
  18. audioguru2

    Car battery..........

    Hi Yourwins, Are you trying to protect your wiring from melting or causing a fire by limiting the current to 30A? Why not do the same as car manufacturers, use a 30A fuse or breaker and a label that says, "Do not exceed 30A".
  19. audioguru2

    non logic level multiplexar

    Hi Ldaniel, Hey, aren't you near that volcano mountain in Usania that blew its head off? Did you see it happen? And you're surrounded by a few other beautiful dormant volcanos? Neat! I don't think you need a unity gain amplifier to follow the multiplexer, since the input impedance of an A/D is...
  20. audioguru2

    "Soft" LED Chaser w/ acceleration?

    Hi Christoph, I have made many chaser projects. Firstly, the output current of an ordinary 4017 is too low to drive LEDs brightly, unless you use a high supply voltage that will cause a 4017 to exceed its max output power. Therefore you will need to use output transistors. The transistors have...
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