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  1. Audioguru

    Rechargeable LED pairs - how do these work?

    The 12V adapter probably has a 4.5V output. If the LEDs are white then they probably use 3.0V and 1.5V is thrown away in a series current-limiting resistor.
  2. Audioguru

    Appropriate power supply for 3 LEDs

    An LED is not an incandescent light bulb with a fixed voltage rating. Instead it is a semiconductor and a "3.2V" LED could be 2.8V to 3.6V. If you want it to operate at 20mA then you must calculate its resistor value properly at its minimum and maximum voltage. If the supply is 5.0V and the LED...
  3. Audioguru

    Design of a transistor curve tracer

    It does not matter if the positive input or the negative input of an opamp "is up" but the feedback usually is negative feedback. You wrongly show three opamps with positive feedback that does not work. I have worked in electronics all my life and have never seen or used a curve tracer.
  4. Audioguru

    Resistors for IR LED's not working?

    Yes, a mistake was made about the IR LEDs or photo transistors. I am glad you didn't mistake them for candy and ate them.:)
  5. Audioguru

    Upper frequency limit of an oscillator

    When I fire up my LTspiceXVII it warns me that the version is four hundred plus days old. But the last time I updated it screwed up really badly but works fine the way it is now.
  6. Audioguru

    Resistors for IR LED's not working?

    Maybe the LEDs are not IR LEDs. The LEDs are in a clear case so their color could be white or blue and have a forward voltage too high for the multimeter to measure or too high for two in series to light from only a 5V supply.
  7. Audioguru

    What to Do With a Lot of Salvaged Speakers?

    The impedance at resonance of many 8 ohm speakers is 40 ohms so having two in series produces no damping at resonance. The damping factor of a modern amplifier is more than 400 so its output impedance is less than 8/400= 0.02 ohms. Then the speaker does exactly what the amplifier signal does. A...
  8. Audioguru

    Resistors for IR LED's not working?

    Your IR LEDs are burned out because: 1) They show a forward voltage of infinity on your diode test. 2) Their current limiting resistor has no current in it.
  9. Audioguru

    What to Do With a Lot of Salvaged Speakers?

    Correction to what I previously typed: 2) Connect two speakers (especially the same kind) in series to the output of a modern low output impedance amplifier and tap the cone of one. The resonance will be damped only a little.
  10. Audioguru

    Upper frequency limit of an oscillator

    Most of us build a real circuit and don't know about in a simulation you can use the .IC statement where you can specify asymmetrical starting conditions which kicks it to begin oscillating.
  11. Audioguru

    Resistors for IR LED's not working?

    In the photo I see clear and black LEDs. Are some of them 2-legged photo-transistors or photo-diodes and not IR LEDs? The connections should be properly soldered together, not just twisted.
  12. Audioguru

    Resistors for IR LED's not working?

    Doesn't your multimeter have a "diode test"? Mine shows the forward voltage of a diode or LED at a very low current. Maybe you burned out your LEDs by connecting the current meter wrong.
  13. Audioguru

    Upper frequency limit of an oscillator

    The values in a simulation are identical and there is no noise to start oscillations. One resistor or capacitor must have a different value than the other one and the circuit might need to be "kicked" to get oscillations started.
  14. Audioguru

    What to Do With a Lot of Salvaged Speakers?

    It is simple to hear a "bongo drum" resonance of a speaker or with two speakers in series: 1) Tap the cone of a speaker that is disconnected. It makes a "bong" resonant sound. Then short it or connect it to an idling modern amp (not an old amp that has vacuum tubes) and tap its cone. It makes a...
  15. Audioguru

    400ma bipolar 12v 2 ohm drain

    Why are you tampering with your car's pollution controls?
  16. Audioguru

    Upper frequency limit of an oscillator

    Maybe it is built on a solderless breadboard and its stray capacitance between all the rows of contacts and wires and inductance of its many long wires prevent the very low value capacitors and very high value base resistors from working properly. Make it with a compact pcb layout using...
  17. Audioguru

    What to Do With a Lot of Salvaged Speakers?

    A speaker has a mechanical resonance frequency that increases when in an enclosure. The sound level increases at resonance. The extremely low output impedance of a solid state amplifier (0.04 ohms or less) damps the resonance creating no peak in the response. Connecting speakers in series...
  18. Audioguru

    What to Do With a Lot of Salvaged Speakers?

    Many years ago I bought a pair of Radio Shack Minimus 7 speakers. They used a long throw 4" woofer and a dome tweeter and sounded very good. Bose probably copied them. The cheap little speakers used in a TV are too small and are not long throw for good bass and there are no tweeters for good...
  19. Audioguru

    Identifying parts of the FM kit

    I think it is an old Sony IC with no datasheet available anymore. Use a more modern IC instead. Its C11 might be a 10.7MHz crystal filter.
  20. Audioguru

    What to Do With a Lot of Salvaged Speakers?

    Bob, you are correct. The little Chinese speakers have a very tiny decimal point that cannot be seen so the 10W speakers are actually 1.0W and the 5W speakers are 0.5W.
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