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  1. audioguru2

    TL072S SIP JFET OP AMPS

    Nice find, John. ;D A perfect Japanese copy of an American IC in a Japanese case.
  2. audioguru2

    white led

    A 5mm white LED is an ordinary one with a max current of 30mA. 20 of them at 30mA makes a load of 600mA on a 6V supply.
  3. audioguru2

    audioguru fm transmitter

    Film/foil capacitors are at least 60 years old and are huge. The modern metalized plastic film caps are small and inexpensive.
  4. audioguru2

    white led

    You forgot to say what the LEDs must do. Drive 20 white LEDs at the same time continuously? Blinking all at the same time? In a chaser/marquee mode? You forgot to say how you will power the LEDs. 6V battery, 12V battery, AC-DC adapter, or powered from a solar panel?
  5. audioguru2

    Newbie Help and Questions

    Hi GNX, Welcome to our forum. ;D A breadboard has many loose wires. Solder the wires directly to the jacks and switches. Your SPDT switch will select between two mono signals. Use a DPDT switch for stereo. Your mute switch will short the signal source which might cause damage to the source...
  6. audioguru2

    ringing detection circuit

    They block signals that have a peak-to-peak voltage of less than 15.6V such as tones and connection clicks. Then the ringer doesn't falsely ring. The ringing signal in Canada and in  the US is 90V RMS which is 255V peak-to-peak.
  7. audioguru2

    LM308 maximum ratings

    Hi Walid, 1) This very old opamp has input transistors with an extremely high current gain. 2) Therefore they have a very low breakdown voltage. 3) So the inputs have back-to-back protection diodes between them to conduct when the differential input voltage exceeds about 0.6V. 4) If the...
  8. audioguru2

    transistor as a switch

    The output transistor passes the load's high current. Its driver transistor operates at a much lower current, just the base current of the output transistor. An emitter-follower  transistor with a high current has a higher Vbe than a transistor with a low current.
  9. audioguru2

    TL072S SIP JFET OP AMPS

    Hi Zap, I hope the replacement dual opamp works in your circuit. It doesn't have FET inputs so maybe its input bias currents will be too high. Its slew rate is as low as an old 741 that has trouble above only 9kHz.
  10. audioguru2

    Urgent help for a transmitter

    Hi Almans, Both your schematics don't show any parts values so we don't know if they will or ill not work. The 2N3906 looks odd and the coil L1 is missing a tuning capacitor in your second circuit.
  11. audioguru2

    Urgent help for a transmitter

    You changed the transistors but you forgot to tell us which ones you used. You forgot to show your pcb so we can see if the wiring is short enough for 100MHz. At 100MHz, a wire is an inductor. If the wire is longer than about 3mm then the inductance is too high. Wires side-by-side have...
  12. audioguru2

    TL072S SIP JFET OP AMPS

    The TL072 dual opamp comes in an 8 pins DIP package, not 9 pins and not SIP. I have used thousands of TL072 opamps but i have never heard of anTL072S. Maybe the "S"version is the one that Toshiba copied but made a mistake and they all oscillated. Maybe the "S" version is the one that Toshiba...
  13. audioguru2

    Sound Level Indicator

    Hi Jon, Yes the LM3915 has a range of only 30dB. But I designed the circuit to have an additional 20dB of automatic gain control. For low level sounds, the input is indicated directly on the LEDs of the LM3915. For low level sounds, the Rhi voltage of the LM3915 is set by the voltage divider...
  14. audioguru2

    transistor as a switch

    No. It is about 1.3V, not a percentage of the supply voltage. The output of a 555 has a darlington emitter follower to pull its output high. It is two base-emitter junctions in series. 0.6V + 0.7V= 1.3V.
  15. audioguru2

    LM308 maximum ratings

  16. audioguru2

    IC controlled emergency lamp with charger

    Hi Walid, Without the diode a 555 will not have equal charge and discharge times. The capacitor charges through R3 plus R4 which is a higher resistance that the discharge resistance of only R4 by itself. With the diode then the capacitor begins charging slowly by R3 plus R4 until the voltage...
  17. audioguru2

    Sound Level Indicator

    Hi Jon, My circuit is very sensitive since it indicates a pin dropping on the floor fairly far away. It indicates that my quiet refrigerator is running. It indicates that I am breathing quietly. Its range is probably from 45dB to 95dB. If you have it as sensitive as 30dB then it would show...
  18. audioguru2

    Simple Unipolar Stepper Driver

    A power darlington transistor has double the base voltage of a regular transistor. Then another diode must be added to the existing ones. I would just use TIP31 transistors and an LM317 adjustable regulator to set the base voltage for them all.
  19. audioguru2

    0-30 Vdc Stabilized Power Supply

    It would be a lot different from this circuit. It would have more than 500W of heating to be cooled.
  20. audioguru2

    Simple Unipolar Stepper Driver

    I haven't seen a stepper operating from a current-limited higher voltage. Maybe the current in the inductance builds up faster when the voltage is higher. But it seems to be a huge waste of power in the current-limiter. There are many ways to reduce the width of the pulses so that overheating...
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