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  1. Audioguru

    555 timer output clipped

    Instead of lowpass filtering a squarewave to make a lousy looking triangular waveform, why don't you make a good triangle waveform with an opamp as a comparator and another opamp as a real integrator?
  2. Audioguru

    Hello, can somebody help me with an240P

    Years ago, Philips invented the TDA7000 FM radio IC and many of its circuits and pcb are shown in Google Images. It was a superhet but oddly used low frequency opamps for its IF amplifier. It was tuned with a variable capacitor, variable inductor or a variable voltage. Its performance was poor...
  3. Audioguru

    Hello, can somebody help me with an240P

    An FM discriminator is only a tiny part of an FM radio. The Japanese one you bought is old and its datasheet says it is sold for maintenance only, not for new products.
  4. Audioguru

    Arduino + Audio Amplifier Board Help

    A speaker never has a resistor in series with it and it never has DC in it like yours will have if one of its wires is grounded. The DC causes the speaker cone to move toward one side making its sounds faint and causes a lot of heat in it.
  5. Audioguru

    Arduino + Audio Amplifier Board Help

    Your speaker (squeaker?) gets hot because it is tiny. Also it might not be loud enough. It looks like you have the filter at the output of the amplifier but instead it must be at the input. This audio amplifier has two bridged outputs. Then each wire of the speaker has its own amplifier and the...
  6. Audioguru

    Arduino + Audio Amplifier Board Help

    I like to hear speech with a cutoff at 15kHz or higher. Old deaf people cannot hear frequencies higher than 1kHz. Do you hear an old telephone well that cuts frequencies above 2700Hz? I looked in Google for Arduino text to speech and found many circuits. Here is one using an ordinary LM386...
  7. Audioguru

    Arduino + Audio Amplifier Board Help

    With a cutoff at 482Hz I doubt you will understand anything in speech. With a 1200Hz cutoff it is only slightly better but is still extremely muffled. Old fashioned telephones had a cutoff of about 2700Hz and the most common phrase was "What did you say?". AM radio has a cutoff of about 3500Hz...
  8. Audioguru

    Arduino + Audio Amplifier Board Help

    Vowels in speech are grunts and groans and reach about 3kHz. Consonants in speech are important for understanding and reach about 14kHz. Tea or fee? Sim or him? The words Failing and Sailing sound the same without hearing the high frequency consonants.
  9. Audioguru

    Arduino + Audio Amplifier Board Help

    The class-D oscillator in the PAM8403 is at 260kHz so it might beat with your PWM oscillator. Maybe the ebay amplifier uses a Chinese version of the PAM8403 that has a defect in it. Maybe the amplifier has a solder short on it.
  10. Audioguru

    Arduino + Audio Amplifier Board Help

    What is the part number of the audio amplifier IC?
  11. Audioguru

    Simple Uninterrupted Power Supply Circuit

    Energizer and a Japanese battery company recommend a trickle charge current of C/40 or less for good battery life. Your C/20 causes a long charging time and a fairly high overcharge current. The Ni-MH manual from Energizer shows that the battery voltage drops when fully charged which will cause...
  12. Audioguru

    Op amp problem ua741

    No, its inputs cannot deal with rail-to-rail input voltage swings since with a plus and minus 15V supply its minimum input voltage range is only plus and minus 11.5V. That is why its minimum supply voltage is plus and minus 5V. Its minimum output swing in to a 2k load is 3V less than each supply...
  13. Audioguru

    Microphone for low frequency recording use

    A horn to concentrate very low frequencies must be enormous.
  14. Audioguru

    Microphone for low frequency recording use

    A speaker has a resonant frequency where it is very sensitive which makes it sound "boomy" as a microphone. An electret mic does not show a resonant frequency and probably produces frequencies very low (lower than audio).
  15. Audioguru

    Op amp problem ua741

    The design of the 741 opamp is 50 years old and it was designed to use only a plus and minus 15V supply. The input common-mode voltage range does not include its input voltages being within 3V from the positive or negative supply but your input is at its negative supply of 0V where it does...
  16. Audioguru

    Squawk Box

    The C1390 is an old Hitachi 2SC1390 that is almost the same an many ordinary little transistors except its pins are in the Japanese sequence of ECB. European BC547 pins are CBE sequence and American 2N3904 pins are EBC sequence. I do not know the other parts you listed.
  17. Audioguru

    What's the name of this circuit?

    As the variable resistor resistance is decreased then the base current in the transistor will increase until the variable resistor and/or the base-emitter junction of the transistor will burn out. There is no such thing as "an LED having a harder leading edge". When the transistor's base...
  18. Audioguru

    Having trouble building circuit?

    The sloppy wiring mess caused the circuit not to work properly.
  19. Audioguru

    Non-inverting audio Op-Amp

    Are you attenuating the input so that you can feed it into the tape playback preamp? It won't work well because the tape playback preamp has frequency equalization.
  20. Audioguru

    Having trouble building circuit?

    Making an electronic circuit on a solderless breadboard is a tangled mess of wires all over the place.
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