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  1. Audioguru

    Back to the Breadboard

    The original schematic posted today uses a Jfet-input TL082 dual opamp which has an extremely low input current. I do not know why it is a dual instead of a TL081 single one. The older NJM4558 dual opamp uses ordinary input transistors with 2500 times more input bias current which reduces the...
  2. Audioguru

    Back to the Breadboard

    1) If the voltage divider measures only 3.8V then your 9V battery is almost dead at only 3.8V x 2= 7.6V and its voltage will continue dropping. Maybe the opamp is defective and is drawing a high battery current? 2) If pin 3 reduces the voltage at the end of the 1M resistor to 0V then either the...
  3. Audioguru

    Back to the Breadboard

    Pin 3 on a single or dual opamp is the + input that must be fed the half supply voltage produced by the 2-resistors voltage divider then fed it through the 1M resistor. The switch has nothing to do with it since the input capacitor blocks any DC from the switch.
  4. Audioguru

    The Final Act

    Amazon sells clothing and a few cheap electronic parts with no specs and frequently they do not even know who made the junk. I buy most reliable electronic parts from Digikey or Newark and if I order before 8:00PM it is delivered to me in Canada the next morning.
  5. Audioguru

    Whistle responder circuit

    My daughter bought a "keys finder" whistle detector. It was triggered by almost any sounds and was useless. This very simple circuit will probably do the same and even be triggered by its own beeper.
  6. Audioguru

    The Latest Build

    In You Tube videos, guys on the other side of the world carry around the solder on the dirty tip of their overheating cheap soldering iron. ebay ads say the connections are welded, not soldered.
  7. Audioguru

    Amplifer improvement advice please

    The Hackaday schematic is completely wrong.
  8. Audioguru

    Overheating resistors in guitar amp

    42V input and 16V output wastes 26V and produces a current of 79mA in the 330 ohms resistor. It heats with 2.05W. A 2.5W resistor will get very hot.
  9. Audioguru

    Back to the Breadboard

    Here are the input and output of your circuit:
  10. Audioguru

    The Latest Build

    It sounds good. Did your dog eat the knobs off the pots?:)
  11. Audioguru

    Regulated 12v Supply, Hum reduction

    Most power supplies use a full wave rectifier bridge that produces 120Hz, not 60Hz. Then one or two of your rectifier diodes do not work.
  12. Audioguru

    The Coffee Sip Tip

    Old fashioned 60/40 tin/lead solder takes time to harden. Newer 63/37 tin/lead solder hardens immediately then motion does not affect the solder joint. Usually rosin-core solder is used. Lead-free solder is completely different so I have never used it since I do not eat tin/lead solder.
  13. Audioguru

    Does the capacitor turn the polarity of the voltage

    Absolutely not! There is no positive voltage since the positive output from the bridge rectifier is at ground (0V). Then the bridge rectifier output is a negative voltage that is filtered with C2.
  14. Audioguru

    Back to the Breadboard

    101 is 10 followed by one zero= 100pF. 102 is 1000pF which is 1nF. 103 is 10nF. 104 is 10nF which is 0.1uF. 105 is 1uF.
  15. Audioguru

    Back to the Breadboard

    The new capacitors are 10nF which is 10000pF. They cut all high frequencies when the gain pot is a high resistance.
  16. Audioguru

    Op Amp Substitute?

    The perfboard photo in the Instructable shows one CD4093 IC with 14 pins and 4 logic gates in it but only 2 of the gates are used. It also shows one dual opamp with 8 pins but only one of the two opamps is used.
  17. Audioguru

    Op Amp Substitute?

    The Instructables circuit does not use a CD4094 and needs only 2 of the 4 logic gates in one CD4093. The 2 unused gates in the CD4093 are not properly disabled.
  18. Audioguru

    Op Amp Substitute?

    The minimum supply for your Japanese NJM4558 is 8V which a 9V battery will soon drop below. Texas Instruments recommend a minimum of 10V for an RC4558.
  19. Audioguru

    Op Amp Substitute?

    The circuit in the video produces noises, not theremin music. The squarewave output will sound like a variable-pitch buzzer. A theremin hand-distance volume control is missing. I think static electricity in winter will destroy that very simple circuit. The output volume control badly has DC in...
  20. Audioguru

    Back to the Breadboard

    You reduce the resistance of the gain pot which reduces the gain by "turning its knob counter-clockwise". The gain pot is a variable resistance from zero ohms to 500k ohms. When the pot resistance is zero then the opamp gain is 1 (the input level is the same as the output level). When the gain...
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