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  1. Audioguru

    Circuit design

    The input voltage to the first opamp never goes positive, then its output also never goes positive. Its input is 0V or is driven negative. All the circuits shown on Google use an inverting opamp that produces a positive output when the input capacitor causes its input to go negative, or biases...
  2. Audioguru

    Beginner question : 555 timer pin 4

    An LM317 must have an input capacitor and an output capacitor, you have none. An LM317 should have a resistor between the output and its ADJ pin of 120 ohms but yours are much higher and variable. The output of an LM293 comparator can drive to ground but is disconnected when it goes "high". It...
  3. Audioguru

    Amplifier the smartphone headphone port voltage

    Feed the headphones output from the phone into the input of a more powerful amplifier. Then the IR LEDs might be destroyed.
  4. Audioguru

    Speaker power (wattage) and consumption

    Many amplifier and speaker manufactures lie about their maximum allowed power ratings. They makeup the power numbers to be 2 times to 10 times the truth. A car amplifier advertised to produce 200W really produces only 15W per channel for a real total output power of 60W. The output power rating...
  5. Audioguru

    Li-ion battery pack

    That charger has many functions that you pay for but you will never use. It has a 5A output that might explode your battery. You did not tell us what battery cells you used that the charging current should match. A 4S pack will overpower the drill and might release its magic smoke.
  6. Audioguru

    18650 Under voltage protection

    Many videos on YouTube show fake 18650 lithium cells with FIRE in their name sold on Chinese websites.
  7. Audioguru

    old telephone bell

    Does anybody know the telephone ringer voltage and frequency in Austria? An old North American telephone had two bell heads and the electromagnet hammer toggled between them. I cannot remember if the frequencies of the two bell heads were different to make a musical chord. Here is a photo:
  8. Audioguru

    what is the different between speaker wire and power wire

    At home I use 16 ga stranded copper lamp cord wire. I tried 14 ga but it made no difference to the sounds. 10 ga wires are train tracks.
  9. Audioguru

    old telephone bell

    I worked with telephone systems in Canada in the '80ies. The ringing was 90VAC at 20Hz. The ringer mechanically resonated at the 20Hz and 50Hz or 60Hz probably will not make it work. Other countries used different voltages and frequencies, but since you did not fill in your location then we are...
  10. Audioguru

    Simple multitester

    Your very old circuit might not work when the silicon PNP transistors are damaged by avalanche breakdown of the reverse biased emitter-base junctions since the supply voltage of 9V is too high without having protection diodes. The maximum allowed reverse emitter-base voltage is shown on the...
  11. Audioguru

    dangling emitter circuit?

    Beware of analog circuits from a computer engineer in India. The circuits Gallery website even has a door intercom with only one amplifier! Two paralleled mics and two paralleled speakers. You talk and your voice is heard at the outside door and severe acoustical feedback howling at your...
  12. Audioguru

    Where to get 4 pin to 2 pin 3.5mm adapter

    A 4 pins 3.5mm plug has mic, left earphone, right earphone and ground. Instead of trying each pin to see which one is mic then I would cut off the 4 pins plug and replace it with a 2 pins plug. The mic is probably an electret type (not a dynamic type) and the car stereo is probably expecting an...
  13. Audioguru

    6v to 12v conversion for toy car

    if the car moves slower than when it was new then maybe the 6V battery needs replacement.
  14. Audioguru

    Need to build a circuit + Power supply check plan for me

    Pin 7 of the opamp is its positive power supply pin. Yours is disconnected. None of your parts have numbers like R1, R2, R3 etc and the part number of the voltage regulator is not shown. The stripboard is missing the very old and obsolete BC109 transistor.
  15. Audioguru

    auto scan fm radio problem

    It might be a copy of the scanning FM "radio" I bought for $1.00 at the Dollar Store. It uses a Chinese copy of a Philips TDA7088 FM radio IC that does not work well. The radio came with earphones and a battery so the actual radio was free.
  16. Audioguru

    Theory/reality mismatch in a transistor circuit

    Exactly. It probably is not 3.8mA, it depends on the current gain of the transistor when it is saturated and the actual forward voltage of the LED and the tolerance of a few other parts.
  17. Audioguru

    Theory/reality mismatch in a transistor circuit

    How do you know the base current when an unknown current feeds the LED? Beta is when a transistor is an amplifier with plenty of collector to emitter voltage. Here the transistor is saturated so beta does not apply and the collector current is usually 10 times the base current.
  18. Audioguru

    Theory/reality mismatch in a transistor circuit

    The first photo shows a 1k resistor parallel with two 10k resistors, not three 10k resistors.. The second photo shows a white or bright green LED, then it is not 1.63V, instead it is 3V or 3.2V at the low current.
  19. Audioguru

    I need user manual

    Amazing if it still works because it is exactly as old as me. But I still work pretty well, better than when I was younger.
  20. Audioguru

    Need to build a circuit + Power supply check plan for me

    I use a red pencil and mark an "X" where I cut the tracks. I also make straight lines, not scribbles.
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