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  1. audioguru2

    0-30 Vdc Stabilized Power Supply

    You don't need to blow it up by seeing that it doesn't make 3V at 3A without overheating. You don't need to see that it doesn't make 30V at 3A. You don't need to see a very high amount of ripple on its output at any output higher than 25V and at 3A. Just pretend that it works very well.
  2. audioguru2

    Two PCBs off of one power source

    You added a 1M mixing resistor in series with a 0.22uF DC-blocking capacitor from the output of the effects circuit which is fine. I think the effects circuit must have a resistor from its output to the supply to simulate its speaker. The FRS volume control might not be able to adjust the volume...
  3. audioguru2

    Help With Ground Please

    To measure continuity you must remove the batteries. Then the negative supply will not be shorted to 0V and the positive supply will not be shorted to 0V.
  4. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Omni, Maybe you are afraid to make basic tests of the power supply at its max rated voltage, current and heating power because it will fail?
  5. audioguru2

    Electronic Stethoscope

    Hi Philip, Get the TL072CP. It is for mounting on a circuit board with its leads through holes. The "D" is a tiny surface-mount package which is difficult to solder. The "A" has very high spec's for the military. The datasheet describes these things.
  6. audioguru2

    Are datasheets important?

    Hi AN920, Of course a HF-switched, crystal-controlled and  Mosfet-output inverter is more modern but I was talking about this 500W inverter project that we have that came from the dark ages.
  7. audioguru2

    Electronic Stethoscope

    The pot is an ordinary volume control. Its resistance can be 2.2k, 5k or 10k ohms. It should have an audio-taper for it to be a volume control intead of having a linear taper.
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Omni, It is easy to make basic measurements of the power supply: Voltage Test: 1) Set the current pot to max and set the voltage pot for 30.0VDC at the output without a load. 2) Then connect a 10 ohms 100W resistor to the output. 3) Measure the output DC voltage and the output AC voltage...
  9. audioguru2

    Electronic Stethoscope

    One of our members, Dazza, used the Electronic Stethoscope-2 project to hear his unborn baby's heartbeat. The circuit has plenty of gain.
  10. audioguru2

    Are datasheets important?

    Hi AN920, If you were designing this 500W inverter, would you use a huge, expensive and poor tolerance non-polar 4.7uF capacitor with a 100 ohm resistor in its CD4047 oscillator, when the manufacturer of the CD4047 recommends using a minimum of 10k for the resistor? Each IC would make a very...
  11. audioguru2

    Timed Beeper...need help!

    Yes, surface mounted capacitors are capacitors. This site messes up "u" symbols. Look at the original project at RED Circuits to see that it is a 25uF electrolytic capacitor. The emitter-follower provides only about 2.3V to the piezo sounder when the 3V battery is new and less voltage when the...
  12. audioguru2

    3mm Jack Audio switcher

    A double pole switch has two completely separate switches with one toggle. Perfect for stereo. A double throw switch connects to the first terminal with it switched one way and connects to a second terminal when it is switched the other way. Perfect for selecting one of two signals. I am in...
  13. audioguru2

    Problem With Ultrasonic Motion Detector

    Go to www.datasheetarchive.com and get the datasheet for the CD4060 oscillator/counter. Connect a 2.56MHz crystal in its oscillator and take 40kHz from its divide by 64 output. Or use a 1.28MHz crystal and get 40kHz from its divide by 32 output. The CD4000 is a series of hundreds of Cmos logic...
  14. audioguru2

    white led

    5 LEDs in series need about 17.5V and the LM317 current regulator needs a minimum of 3.75V so a voltage more than 21.25V would be fine. Use an 18VAC transformer then the unregulated voltage will be 23.8VDC.
  15. audioguru2

    Problem With Ultrasonic Motion Detector

    Sorry, I haven't used old 74xx TTL logic ICs for many years. I used to have a TTL Cookbook that was very useful for connecting those very old ICs. The 7490 is probably explained on the internet. I have used CD4000 series Cmos and 74HCxx high speed Cmos ever since. They have dual divide by 10...
  16. audioguru2

    12v power supply?

    If you know nothing about electronics then use 8 AA alkaline battery cells in series. It will make 12V when the cells are new.
  17. audioguru2

    Are datasheets important?

    I have no respect for an engineer who made 7 mistakes on a simple inverter project.
  18. audioguru2

    Need sugestions about virtual ground or symetric supply for OPAMP

    The buffer opamps don't do anything. They are ordinary opamps that have a max output current of only 15mA peak. If the load capacitance is very high then the load is the 100 ohm resistors which overloads ordinary opamps.
  19. audioguru2

    Electronic Stethoscope

    I answered your Personal Message. I didn't know you posted the same questions here. U1a and U1b are a TL072 which is a dual opamp. It has two low noise opamps inside. Look at its datasheet. U1a is a preamplifier. U1b is a Sallen and Key 2nd-order Butterworth lowpass filter that cuts frequencies...
  20. audioguru2

    Need sugestions about virtual ground or symetric supply for OPAMP

    Hi Wellington, I use Microsoft Paint program to modify schematics. Your circuit has R23, R24, IC3B and IC3C that don't do anything.
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