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  1. audioguru2

    BJT biasing formulas

    R5 provides negative feedback at lower audio frequencies. At 10kHz and above, C4 bypasses it for high voltage gain and high distortion but you can't hear the 20kHz to 30kHz distortion harmonics. Here they are:
  2. audioguru2

    Class D amplifier Applications

    Good ones sound very good, nearly hi-fi.
  3. audioguru2

    Question on the Plants Watering Watcher circuit

    Hi Satty, Welcome to our forum. ;D The circuit of the Plants Watering Watcher-2 produces a logarithmic output so it shows a very wide range of moisture levels. It would be difficult to make it linear, so use your microcontroller to convert from logarithmic to linear. I have removed its blinking...
  4. audioguru2

    Telephone Ring Circuit

    Hi Aan, Are you making an intercom with phones? I don't know if phones in your country are the same as mine. My phones need a 90VAC/20Hz signal across tip and ring to activate their ringers.
  5. audioguru2

    Sound Level Indicator

    It blocks DC so that IC1a has a DC gain of 1 like a follower with its DC output voltage averaging +2.5V, but allows an AC gain of 101. If R6 is connected to ground then the DC gain of the opamp would be 101 and its output would be saturated at near +5V, because R2 and R3 bias its input at...
  6. audioguru2

    BJT biasing formulas

    Hi Walid, Negative feedback reduces a transistor's voltage gain and distortion and increases its bandwidth and input impedance. Where gain is more important than low distortion or wide bandwidth like in a child's toy walkie-talkie then a CE is added. If a current source is used as the collector...
  7. audioguru2

    a high pass filter question

    Hi Walid, An opamp or transistor can't drive 160 ohms but they can drive 1.6k or 16k. A 10uF cap costs more and is bigger than a 1uF cap. A 0.1uF cap might cost even less. If the R is too high and the C is too small then the input of the next stage must be a very high impedance which might...
  8. audioguru2

    Comparator usage.. Help!

    Your power supply should have a 100uF bypass capacitor across it. The max input offset voltage of an LM393 is only 9mV. Yours is much more so it must be bad.
  9. audioguru2

    Comparator usage.. Help!

    The 1M vaue of the pot is way too high. If the comparator has its max rated input bias current of 250nA then at 2.5V the error is 0.175V. Maybe your comparator has too much input bias current. Replace it to see. Even the input resistance of your voltmeter will load down the voltage of the 1M...
  10. audioguru2

    Telephone Ring Circuit

    It has a capacitor-coupled mechanical ringer or a capacitive-coupled ringer IC that drives a speaker. Here they are driven by a 90VAC/20Hz ringing signal. When a phone answers the ringing then the phone draws DC current from the phone line. When the PBX detects DC current then it stops the...
  11. audioguru2

    Telephone Ring Circuit

    Hi Aan, The PBX's I worked with in Canada used ordinary single line phones and used a 90VAC/20Hz ringing signal. Old systems used relays to connect the ring generator to the line, but newer ones used triacs.
  12. audioguru2

    Comparator usage.. Help!

    Hi Salvatore, Welcome to our forum. ;D You didn't attach your schematic showing all resistor values so I am just guessing. The comparators don't have an output transistor that pulls up, an added resistor must do it. If the hysteresis resistor has a value too low then it will load-down the output...
  13. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Hi Steven, It Sort-of works! ;D How many Watts is the light bulb rated for? You said it wasn't fully bright so it was glowing at less than its rated power. Your voltmeter is calibrated to read sine-waves unless it is "True RMS", so it probably shows a higher voltage that is actually there...
  14. audioguru2

    Problems with my 555 circuit

    I think his voltage source is a secret. A windmill! 0V when it is calm and 100V during a hurricane.
  15. audioguru2

    Problems with my 555 circuit

    Sorry Bob, I thought you were the guy who tried to blow up his 555 and LEDs.
  16. audioguru2

    Problems with my 555 circuit

    Hi Bob, You still didn't say what is your supply voltage. The output low of a 555 can't go to a negative voltage. It goes to almost ground. Look at the datasheet for the 555. With a 20mA load connected to ground, the output high goes to 1.4V less than the supply voltage. With a 20mA load...
  17. audioguru2

    How I can make a headphone amplifier

    The old LM324 has crossover distortion, is noisy and cannot produce max output above only 6kHz. It is too old and lousy for good audio. The old LM358 is a dual version of the old quad LM324. They might make a fuzz geetar sound if you like it.
  18. audioguru2

    Can't find this part....

    I entered the part number in Google and got many links with datasheets.
  19. audioguru2

    How I can make a headphone amplifier

    Get a TL072 dual opamp. Then the 1st one can be the non-inverting opamp with a gain of 1 and a 1M input resistor to ground and the 2nd can be the preamp.
  20. audioguru2

    Problems with my 555 circuit

    If your battery was strong enough then the LEDs and the 555 are burned out. The resistors limit the current. You still don't say how many volts is your power supply or battery. The resistors and capacitor values cause the 555 to oscillate at 10Hz. The resistors cause one LED to be on 19 times...
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