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  1. Audioguru

    Can I re-use old components?

    If the input signal level is very low from a microphone, phono cartridge or tape head then use metal film resistors for reduced noise. For line level the tiny noise from carbon film resistors will not be heard. EDIT: Don't buy the parts from ebay.
  2. Audioguru

    Problems with sound circuit on a toy train

    You Tube uses cookies to play something that you watched before. Pretty girls at the beach?
  3. Audioguru

    Calculating Battery Usage

    You might assume that the battery is lead-acid and its 50Ah is 5A for 10 hours. It is easy to calculate the total average current since you were given the duty cycles. Fudge the discharge time a little lower since the transmit is higher than 5A. 30 hours?" No Way! Two batteries in parallel will...
  4. Audioguru

    DC-DC Converter

    On another website Joe Wu was trying to attach his images to links at the All-About-Circuits website but they also did not work.
  5. Audioguru

    why is this comparator triggering on falling edge?

    The datasheet for the TL08x and TL07x opamps says that the input common mode voltage range is -12V to +15V when the supply is +15V and -15V (so the inputs do not work properly when within 3V from the negative supply). They do not say that then the output suddenly goes positive like this:
  6. Audioguru

    Can I re-use old components?

    The silicon transistors should be fine. Polyester, ceramic and polycarbonate capacitors should last forever. Tantalum and electrolytic capacitors should be replaced with the same types as the originals. 15nF, 47nF, 3.3nF and 220nF are probably polyester type capacitors. Use 2% metal film for the...
  7. Audioguru

    LED VU/PPM-meters -metering scales and their use

    Correct.
  8. Audioguru

    LED VU/PPM-meters -metering scales and their use

    Some of my electronic recorders have an LED display of level that is calibrated so that the highest levels are when they produce overload distortion. I have a "VU" meter with microphone in my family room with a range of 50dB and it is not calibrated, but the highest LED shows very loud levels...
  9. Audioguru

    A simple one with LED strip

    There is a huge city in China where they make only fake electronics. Most is sold on ebay, Alibaba and Amazon. How do you know if something there is real, fake or poor quality? Digikey and Newark do not sell that junk.
  10. Audioguru

    Can I re-use old components?

    I have many old electronic products that I take parts from. I do not re-use an electrolytic capacitor that has a bulged top and I do not re-use high power switches that have tarnished silver contacts that do not conduct low currents. I always bought switches and IC sockets with gold plated...
  11. Audioguru

    A simple one with LED strip

    The quality of an LED strip determines how long it lasts. A cheap no-name-brand LED strip made with a manufacturer's rejected LEDs and sold on ebay might last one week. A good one will last for 50000 hours which is 11.4 years worth of nights.
  12. Audioguru

    TDA 7000 FM radio can't tune in any station

    The article has an error, it says the LM386 power amplifier is set for a voltage gain on 20 and wrongly says it is 40dB. A gain of 20 is actually a gain of 26dB. A voltage gain of 40dB is a gain of 100.
  13. Audioguru

    Passive low-pass filter

    A capacitor at the output of an amplifier (across the speaker) is a short circuit to high frequencies and many amplifiers blow up when driving a short circuit. Audio is AC. A polarized capacitor is used only with DC and it, the amplifier or both might blow up when it is fed the AC from an...
  14. Audioguru

    Passive low-pass filter

    An active crossover filter avoids the problems of passive filters at the speakers. The resistance of the inductor in a lowpass passive filter ruins the damping of resonance from the amplifier and the result is a bongo drum at one frequency.
  15. Audioguru

    Help with powering a circuit board

    A 5V charger does not have a regulated voltage. It might be 10V or more when it has a low current load that might blow up your screen.
  16. Audioguru

    Passive low-pass filter

    A filter is connected to the input of the amplifier, not the output. 1k ohms in series with a 1uF capacitor to ground reduces high frequencies but is too simple to cutoff anything. 160Hz will be reduced a little (-3dB), 320Hz will be reduced a little more, then more gradual reduction of higher...
  17. Audioguru

    TDA 7000 FM radio can't tune in any station

    The capacitance between the wires and rows of contacts on a breadboard causes problems when a circuit uses a frequency higher than a few kHz. FM radio is ten thousand times higher. The TDA7000 IC is very old and had very poor performance. I can buy a cheap Chinese radio for $1.00 at The Dollar...
  18. Audioguru

    Huming sound in homemade bluetooth speaker

    Your photo of the wiring shows ordinary wires all over the place. Your schematic shows two wires for each speaker but only a single wire at the amplifier input that might have its shield disconnected so this wire is an antenna that is picking up 50Hz mains hum that is all around you. The shield...
  19. Audioguru

    Huming sound in homemade bluetooth speaker

    The Chinese amplifier already has bridged amplifiers for both its stereo channels. That is how it produces 15 Whats (10 Watts) into 4 ohms per channel when powered by only 12V. The hum comes from the inputs (maybe unshielded wires or a ground loop) or from the power supply. Does the hum go away...
  20. Audioguru

    LED project, heat dissipation

    It is illegal to modify lighting on motor vehicles in Canada to prevent do-it-yourselfers from getting the brightness, viewing angle and color wrong. I hope that you will never be driving in front of me at night, or on a corner when I drive past.
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