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  1. Audioguru

    120VAC --> 12V LED chip

    The 31V LED module has fifty 1W LED chips in it. The instructions written in horrible Engrish say to use the LED chip to rub thermal paste on your back. Each chip is about 3V so they must have rows of 10 LED chips in series and the 5 rows are in parallel.
  2. Audioguru

    120VAC --> 12V LED chip

    21.3mA x 31V= 0.66W which is much less than the 50W maximum power of the LED. 21.3mA is good for an ordinary little LED.
  3. Audioguru

    120VAC --> 12V LED chip

    A 50W LED will need a massive heatsink. If only one LED is used in that simple circuit then it will flicker on and off at 30Hz.
  4. Audioguru

    FM transmitter hack

    That is a great way to break the law and cause radio interference to anybody nearby who is listening to an FM radio station or to their low power FM transmitter. Good luck trying to find the "black box" that reduces the signal strength since yours is different to the Instructable.
  5. Audioguru

    need help with fm transmitter

    An ordinary FM transmitter transmits from 88MHz to 108MHz. Its coil is about 100nH with 5 to 9 turns of wire on a 3mm inside diameter former. But this circuit uses a lower value coil so its turns are fewer and its frequency is much higher. Do you have a radio that will receive it? C7 is not...
  6. Audioguru

    Different Pass filters for different speakers.

    A quick look at the datasheet of the TDA2030A shows that its maximum allowed output current is 3.5A peak so that its maximum output power to a 4 ohm speaker is 22W if the supply voltage is 36V. But the maximum allowed output current for an opamp is only about 0.02A then its output power to a 4...
  7. Audioguru

    Need help building a speaker.

    You neverconnect a capacitor across speaker terminals because it will be a dead short at high frequencies to the amplifier and the amplifier might be destroyed if it does not protect itself by limiting the very high current or muting itself. The high frequency levels will not be reduced anyway...
  8. Audioguru

    Circuit with piranha leds

    The datasheet for the CR2032 battery shows that is designed to produce a very low current (0.19mA) for a long time (1300 hours). Then its capacity is 240mAh. If it is loaded with a normal or higher LED current then it craps out very early.
  9. Audioguru

    Need help building a speaker.

    Build a speaker? You mean to put together a magnet, a moving coil and a cone? Or do you want to make a sound system with an amplifier and a tiny speaker? The tiny speaker in the tiny box will sound awful.
  10. Audioguru

    Bluetooth Speaker Amp - Replacing Analog Pot wth Digital Pot

    The datasheet for a digital pot shows how to use it.
  11. Audioguru

    Bandpass filter help

    The lousy old LM358 and LM324 opamps have poor slew rate which causes trouble with frequencies above 2kHz. Instead use a more modern opamp that works fine up to 100kHz. Gain is the amount of voltage amplification. An active filter needs only a certain amount of gain so that it has sharp and...
  12. Audioguru

    Choosing a transistor

    Don't just look at the graphs on a datasheet because they show parameters that apply only to a "typical" device. Most parameters have a range of values that is shown as minimum and maximum in the text of the datasheet because each transistor is different and you cannot buy the exact value for a...
  13. Audioguru

    XR2206 DIY signal generator kit.

    My oscilloscope is 54 years old and I made it as a kit. It is analog and shows a very clear waveform. Many digital 'scopes show a staircase instead of a smooth ramp or sinewave.
  14. Audioguru

    Choosing a transistor

    In high school I was taught about simple electricity, not electronics. I read electronics magazines and learned many things then I designed and made many electronic devices with the details from the datasheets. In university I was taught all the details and about the datasheets that I already knew.
  15. Audioguru

    Different Pass filters for different speakers.

    Wrong. Except at very low levels, a healthy human ear hears from 20Hz to 20kHz perfectly. Old people like me (72 years old) have high frequency hearing loss that is corrected with my hearing aids. Different speakers have different sensitivities then you adjust the volume controls on the...
  16. Audioguru

    Different Pass filters for different speakers.

    Where does this active crossover circuit have only one output? It has 3 outputs, high to the tweeter amplifier, mid to the midrange amplifier and low to the woofer amplifier. The Aliexpress TDA2030A amplifier costs only $0.74US and produces an output of only 2W into an 8 ohm speaker when...
  17. Audioguru

    Not HoWo - Series, parallel, RC low pass

    Your tutorial says that the series RC are "across the input" and the output is "taken across the capacitor only". Which means that they are a voltage divider. As the frequency becomes higher then the impedance of the capacitor drops which reduces the levels of the high frequencies. Is that clearer?
  18. Audioguru

    Circuit with piranha leds

    An LED is not a very hot simple length of tungsten wire (incandescent light bulb), instead it is a diode whose current must be limited by your circuit. CR2032 battery cells are small then can produce only a fairly low current for a very short time. AAA cells can provide much more current for a...
  19. Audioguru

    Choosing a transistor

    Almost every transistor has a voltage rating shown on its datasheet that is higher than 30V so thinking about 3V or 5V is silly. A transistor used to turn on an LED or a motor must be able to provide enough current. If it needs 3A then you select a transistor rated on its datasheet for maybe...
  20. Audioguru

    Not HoWo - Series, parallel, RC low pass

    The capacitor in a simple lowpass filter is not in series, instead the resistor is in series so that the capacitor to ground can cut high frequencies. The higher is the frequency then the lower is the impedance (AC resistance) of the capacitor. A speaker is NEVER fed with a series resistor and...
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