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  1. audioguru2

    Laser Link Communicator

    You can't use 10 ohms to replace a 68 ohm resistor, you risk burning-out the laser diode. Since you can't use the proper NTC, the laser might drop-out when the ambient is cool and burn-out if hot. The photo-diode is backwards in the receiver's schematic, the pcb layout of it is correct.
  2. audioguru2

    Mosfet Latching

    The TL072 dual opamp is so popular in stereo equipment that it costs less than a 741 single opamp. It is low noise, low distortion and wideband. I have used it for about 20 years.
  3. audioguru2

    Mosfet Latching

    The circuit you posted has an LM324 operating at only about 91Hz. The LM324 is low-power and old, so is even slower than a 741. It has trouble above about 5kHz.
  4. audioguru2

    What does it mean when the voltage lower it self up?

    You connected the capacitor backwards. Its negative wire is marked with a minus sign. Replace it and connect the new one the right way around. The new capacitor should have a 25V rating. Don't forget that the 7806 needs at least an 8.5V input, so the 6VAC when rectified and filtered is too low...
  5. audioguru2

    PSpice

    A Spice model of their TL072 opamp is sitting on the website of Texas Instruments for anyone to have. http://www-s.ti.com/sc/psheets/sloj067/sloj067.zip
  6. audioguru2

    What does it mean when the voltage lower it self up?

    A capacitor is designed to block DC current. Your circuit has a capacitor blocking DC current from the rectifier to the regulator. My circuit has the positive terminal of the rectifier connected directly to the input of the regulator. Your circuit has a capacitor blocking DC current from the...
  7. audioguru2

    What does it mean when the voltage lower it self up?

    Look at the huge difference in the wiring of your circuit that doesn't work, and my circuit that works. I don't know what is 1, 2, 3 terminals on your regulator so I copied its pic from its datasheet:
  8. audioguru2

    What does it mean when the voltage lower it self up?

    If you can't post a simple schematic then how can we help you? I use Microsoft Paint to draw all my schematics. With the Shift key depressed, the mouse makes perfectly straight lines. It can copy and paste stuff from other schematics. I copied and modified this tiny schematic and your circuit...
  9. audioguru2

    PNP and NPN replacements

    All Hartley oscillators feed the inverted signal from half the center-tapped coil to the transistor's base. This circuit has the other half of the coil as the collector's load through C3, since the RFC coil is a very high impedance (inductive reactance) at the operating frequency.
  10. audioguru2

    What does it mean when the voltage lower it self up?

    Hee, hee. ;D We speak geek-talk! ;D
  11. audioguru2

    Mosfet Latching

    Hi Alun, Ha, your boosted-output 741 circuit was used with gain in a Korean (Goldstar, now called LG Electronics) speakerphone that I had to install and service in 1980. It had the worst pcb that I've ever seen. The copper was poorly stuck on the pcb with rice stuff. Users all complained about...
  12. audioguru2

    What does it mean when the voltage lower it self up?

    A 7806 regulator needs at least 8.0V on its input to provide voltage regulation when it has a load. Look at its datasheet! The 7VDC input is much too low. If you used 12VAC from the transformer, the rectified and filtered 15.5VDC would allow the regulator to work properly, but it might get hot...
  13. audioguru2

    Mosfet Latching

    I don't use a formula, I just never use a lousy old 741 opamp. I used one as an audio amp in 1965 and it sounded so bad, I never used one again! ;D Over the years I've seen and heard many audio amps with 741 opamps. I think I can recognise their terrible sound. An LM358 or LM324 low-power opamp...
  14. audioguru2

    BJT biasing formulas

    Hi Autir, I don't have formulas; just Ohm's Law, the transistor's datasheet and experience. Your 2nd circuit won't work because the current gain and base-emitter voltage of any certain transistor is different for each one, and change with temperature changes. For the 1st transistor circuit, I...
  15. audioguru2

    What does it mean when the voltage lower it self up?

    How can a 6V regulator IC have a 7V output? It's busted or you have it connected backwards. Please attach your schematic. I also don't know what is a "feedback load resistor", but a 7806 regulator should have a +6V output (within 5%) without any load. It should also be cold without a load. I...
  16. audioguru2

    4017 Problem

    I guess the gain of an AND gate is so high that it would be a nightmare to try to bias the thing to a linear region.
  17. audioguru2

    Amplified Ear help!!!!

    I've used a FET as a voltage-controlled-attenuator. I had a car radio with a cassette recorder that attenuated the signal with resistors then used an ordinary biased diode as a current-controlled-attenuator. It sounded fine. ;D
  18. audioguru2

    Mosfet Latching

    A 100mV input to an opamp with a gain of only 10 results in an output of only 1V. Far from 10V or 20Vp-p clipping. When an opamp's output exceeds its max slew-rate, its output ramps and looks and sounds like a triangle wave. The typical slew-rate of a 741 opamp is only 0.5V/us. A TL071 opamp is...
  19. audioguru2

    12 volt battery charger

    Wouldn't it be easier to trickle-charge the battery over the winter? ???
  20. audioguru2

    Radar Detector

    A radar or laser detector will just give an alert that you have already been "clocked", to allow you to slow down so you don't run over the cop who is waving you over to the side of the highway. You don't need an alert. If the cop is standing in the middle of the highway, that's his problem...
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