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  1. Audioguru

    Can this be repaired by a complete novice please? Basic circuit repair?

    Notice the direction of the side with the writing on it is facing.
  2. Audioguru

    Is this possible to do?

    A phone that is on-hook draws zero DC current. The green LED in the Circuits-Today circuit draws possibly enough current for the system to be off-hook all the time. Then use a battery or isolated power supply to light the LED and hope that the base bias current for the transistor is low enough...
  3. Audioguru

    Will MOSFET be Replaced in the Future?

    "Gonna" is is informal English speech but in Italian it means "skirt".
  4. Audioguru

    Can this be repaired by a complete novice please? Basic circuit repair?

    I can see Q something 5252F on the 4-pins part. The QX5252F is common in most solar garden lights:
  5. Audioguru

    Now the Fun Begins

    The datasheet for a TIP127 shows that it is a power PNP darlington transistor. A BC547 is not a power transistor, is not PNP and is not a darlington. The circuit is very old and was probably designed before a power Mosfet transistor was invented.
  6. Audioguru

    class A push - pull amplifier ?

    Maybe that very old high radio frequency amplifier used little ferrite transformers in it.
  7. Audioguru

    Now the Fun Begins

    The opamps shown recently are missing the very important two resistors at the - input. The resistors set the amount of gain. Without the resistors the gain is a few hundred thousand at low frequencies and with severe distortion.
  8. Audioguru

    class A push - pull amplifier ?

    Anne, the very old book you found shows high radio frequency power amplifiers for a radio transmitter that must be designed properly to avoid interference with other communications and you must have a license to use it. I thought you wanted an audio power amplifier to drive a speaker. Audio...
  9. Audioguru

    MOSFET IC for 3.3v Signal

    The graphs on a datasheet are for a part that has "typical" specs. But many parts have minimum or maximum specs and you do not know which when you buy them.
  10. Audioguru

    Speaker/s project - for amplifier.

    A woofer + tweeter speaker is designed to ,play low distortion music. The severe distortion used for an electric guitar will overload the tweeter and maybe destroy it. The tweeter will have a capacitor feeding it. Cut a wire on the capacitor to stop the tweeter from playing high frequencies.
  11. Audioguru

    Speaker/s project - for amplifier.

    A 10" woofer with the physical tweeter produces most sound frequencies. The woofer produces low frequencies and the tweeter produces high frequencies. The woofer by itself might not produce the high frequencies from a guitar. Try it first before removing the tweeter. Do you know that a speaker...
  12. Audioguru

    Now the Fun Begins

    A laser can easily destroy your vision unless you limit its current and aim it away from people and reflective things.
  13. Audioguru

    Tips on how to cut a pcb

    I use a manual hacksaw with a fine tooth blade.
  14. Audioguru

    class A push - pull amplifier ?

    Distortion is produced by harmonics. The harmonics of 14MHz are at 28MHz, 42MHz, 56Mhz, 70MHz and higher that cause interference to licensed radio communication and will make your circuit illegal. A Metal case 2N2222 is expensive, rare and old but is still available as a replacement. Its...
  15. Audioguru

    class A push - pull amplifier ?

    The emitter resistor in the output transistor stage is never as high as 10 ohms, it is usually 0.1 ohms to 0.33 ohms. The resistors allow matching of the Vbe and current gains of the output transistors. Here is a simple class-AB amplifier using little transistors that are near their maximum...
  16. Audioguru

    routing 2 channel audio to 5.1 speaker system

    Good, then the TV audio source has a very low output resistance (opamps). Absolutely not! An inductor does that, for audio it will be huge. A resistor passes all audio frequencies, ultrasonic frequencies and many very high radio frequencies. The 25 dollars IC is a special very high frequency...
  17. Audioguru

    Just When I Thought it was Going to Be Easy

    You need only a single opamp. I have used many TL071 single audio opamps for hifi circuits but the TL081 is the same. Your original circuit used the TL081. You can make a unique sound. The TL071 and TL081 have a problem called Opamp Phase Inversion. If an input is driven within a few volts of...
  18. Audioguru

    Can BC548 be replaced by 2N3906 and 2N3904?

    The sequence of pins in a BC548 is CBE but the pins of a 2N3904 are EBC.
  19. Audioguru

    Just When I Thought it was Going to Be Easy

    If you want the original tone control range with a 20k pot then change the 22nF capacitor at it to 10nF.
  20. Audioguru

    Just When I Thought it was Going to Be Easy

    At maximum resistance, the 10k tone control cuts 727Hz a little (-3dB) and cuts higher frequencies more at -6dB per octave. A 20k tone control will cut 364Hz -3dB and higher frequencies at -6dB per octave. Good hearing can hear 20,000Hz.
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