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  1. Audioguru

    Connecting a vintage microphone to a PC

    When people are communicating on a system that cuts high speech frequencies like most consonants have, then to be understood they must repeat what they say over and over and use synonyms like Charlie, Foxtrot and Zebra to replace saying the letters C, F and Z. Words beginning with S like Six get...
  2. Audioguru

    Connecting a vintage microphone to a PC

    How can a microphone that cuts off the important consonants sounds in speech create clear voice reproduction? Consonants easily reach 14kHz and without them speech is just vowels with no meaning. Half of a telephone or walkie talkie conversation is, "What did you say? (Six, or fix)?"
  3. Audioguru

    Want to make an Electromyography amplifier circuit.

    Why didn't you learn about them in college or university?
  4. Audioguru

    Want to make an Electromyography amplifier circuit.

    Look at the datasheet of the AD620 instrumentation amplifier and all other instrumentation amplifier ICs. They usually show an ECG circuit that is almost the same as what you want. The INA106 differential amplifier datasheet shows two opamps added to it to make it an instrumentation amplifier...
  5. Audioguru

    Piezo Control voltage source

    The input of the signal conditioner opamp must have D1 and D2 to prevent a high voltage from the piezo from zapping it.
  6. Audioguru

    Want to make an Electromyography amplifier circuit.

    The datasheet for the TL072 and most other opamps shows that its maximum output current is 11mA. If you want the output to have a peak voltage of 5V then the current at high frequencies into the 5 ohms of R2 must be 5V/5 ohms= 1000mA which is 91 times higher that is possible. Why such a low...
  7. Audioguru

    Connecting a vintage microphone to a PC

    The microphone input on a pc is designed for an electret mic which is a condenser mic with its 48VDC stored permanently in its electret material. The mic has a Jfet impedance converter inside that must be powered with the +5V on the mic jack. The current is very low, about 0.5mA. Your antique...
  8. Audioguru

    Piezo Control voltage source

    This is the corrected input protection circuit:
  9. Audioguru

    Want to make an Electromyography amplifier circuit.

    Your schematic has a few serious problems. The 5V supply is too low for a TL072 and it needs an additional negative supply or it should be biased at half a higher supply voltage. Its datasheet shows that its inputs do not work if their voltage is within 4V from a supply voltage. Your inputs are...
  10. Audioguru

    Piezo Control voltage source

    Your signal is attenuated to 1/50th by the first opamp in the VCA. If you switch it to Linear then U1D amplifies it back up 50 times.
  11. Audioguru

    Piezo Control voltage source

    The first opamp in the VCA is a mixer with an input impedance fairly low for a piezo transducer of 100k ohms and no gain. The output of this opamp is 1/50th the input level. It feeds either a pair of Mickey Mouse log transistors (affected by temperature) or a linear opamp with a voltage gain of 50.
  12. Audioguru

    Piezo Control voltage source

    Won't back-to-back zener diodes act like ordinary diodes and limit the input voltage swing to only +/- 0.65V?
  13. Audioguru

    Piezo Control voltage source

    I forgot. You probably do not need RS because the current from a piezo transducer is very small. The input of the opamp must be biased with a resistor to ground if you have +/- supplies. This resistor is the load for the piezo and it determines the highest voltage produced when the piezo is hit...
  14. Audioguru

    Piezo Control voltage source

    The datasheet clearly says the max allowed input voltage is +/- 15V or the supply voltages. What value is your input resistor to ground? Please post your schematic.
  15. Audioguru

    Piezo Control voltage source

    Do it like this:
  16. Audioguru

    Audio amplifier recommendations

    A speaker with a power rating of only 3W is small (no bass) and is cheap (poor quality). It might survive 3W but only for a moment, if it is asked to make a long duration tone then it might be destroyed since the peak power or very distorted power of a 3W amplifier is 6W. A speaker rated at 10W...
  17. Audioguru

    help about this diode

    Measure its forward voltage with the "diode test" on a multimeter. If the measurement is 0.5V to 0.6V then it is a silicon rectifier. If it is 0.15V to 0.3V then it is Schottky.
  18. Audioguru

    30W and 4x8W audio amplifier circuit?

    I have never used a class-D amplifier, all my hifi amplifiers are class-AB. The latest class-D amplifier ICs switch at hundreds of kHz and have very linear PWM so that their noise and distortion cannot be heard and can be barely measured so sure they are hifi.
  19. Audioguru

    Piezo Control voltage source

    You can label your circuit anything you want, it is your circuit. Yes, if the 100k feedback resistor is changed to a 100k pot then it controls the gain from 1 to 11 times. If the piezo is hit hard enough to produce a voltage higher than the supply voltage then the opamp might be destroyed...
  20. Audioguru

    PWM frequency generator for LED's

    A 1kHz PWM frequency will not cause an old fashioned incandescent light bulb to flicker at high shutter speeds but since LEDs turn on and off extremely quickly then you should not PWM the LEDs for a high shutter speed video.
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