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  1. audioguru2

    0-30 VDC Stabilized Power Supply 0.002-3 A

    What will you use to drive the 10 output transistors? 5 or 10 driver transistors that are driven from 5 opamps. Do you really need 30A? For what?
  2. audioguru2

    Connecting a 5w, 12vdc amp to a 12vdc telephone intercom system

    Acoustical feedback howling occurs when the microphone (in the handset) can hear its amplified output from the speaker and the sound goes around and around making a feedback howling sound. It is stopped in a cheap speakerphone by using half-duplex which is allowing the sound to be transmitted or...
  3. audioguru2

    Current monitor/sensor

    Of course the transistors will not work when you need them to work if you use resistors to limit their current. Also the current will still be fairly high and the added resistors will get hot. Why not use Mosfets instead? They use NO base current. When the battery is dead or is missing then the...
  4. audioguru2

    IC for shutter-speed tester

    If the IC is bad then it might damage the power supply. Then the damaged power supply might burn down your house unless it is fused.
  5. audioguru2

    IC for shutter-speed tester

    www.radioshack.com does not list an LM339 IC. Maybe some US stores still have some. I hope the one you found is a real one and not a cheap Chinese fake one. Look at the datasheets of the LM339 at www.datasheetarchive.com where they have an entire list of manufacturers who make it. Find the...
  6. audioguru2

    Blink LED using FM radio

    Many circuits on that website are wrong, especially this one that might NOT be an FM radio. Its transistors are connected with positive feedback that might cause them to oscillate and cause radio interference to a REAL FM radio. Or T2 is saturated and T1 is cutoff and they stay like that. Maybe...
  7. audioguru2

    IC for shutter-speed tester

    The "N" is the type of package. The LM339 in your photo was made by National Semiconductor and has pins so its package is called "N". I do not know what Radio shack sells because they are gone from Canada. Make sure it is in a package that fits in your IC socket. 
  8. audioguru2

    http://servicemanuals.pro - FREE

    It is not free. I pay $5.00 then discover that they do not have the service manual I need?
  9. audioguru2

    Component identification

    It is a surface mount ceramic capacitor without its value marked on it.
  10. audioguru2

    Sonos ZP-100 Custom Robinette Box for Headphones

    50W RMS into 8 ohms is a signal voltage of 20.0V RMS. 100W RMS into 4 ohms is a signal voltage of 20.0V RMS and the headphones will sound exactly the same as with 8 ohms. Maybe the Trueplay equalization for their speakers boosts high frequencies that the headphones play too loudly.  
  11. audioguru2

    Connecting a 5w, 12vdc amp to a 12vdc telephone intercom system

    Your schematic shows a 620 ohms resistor not a 620k ohms high resistance resistor. if it is replaced with 300 ohms then it makes only a little difference.
  12. audioguru2

    Connecting a 5w, 12vdc amp to a 12vdc telephone intercom system

    Of course the input ground pin 7 and the output ground pin 8 both must connect to 0V on the power supply. But if the pins are connected together and a long wire connects them to the power supply then the variable high current from pin 8 in the resistance of the wire affects the 0V on pin 7 which...
  13. audioguru2

    DC-DC converters

    With the inputs in parallel then they work perfectly. Did you connect the outputs of two in parallel? Why? The output of one has a maximum current of 3A. If you need more current then you need a more powerful circuit. You also cannot connect the output of the 5V one in parallel with the output...
  14. audioguru2

    Current monitor/sensor

    No, the opamp and transistors are a follower. 0V input gives 0V output at the 0.5 ohm resistor. +1V input gives +1V output at the 0.5 ohm resistor. +10V input gives +10V output at the 0.5 ohm resistor producing a current of 20A. 220 ohms between the emitter of the BD139 and the bases of the...
  15. audioguru2

    0-30V Stabilized Power Supply

    Motorola/ON Semiconductor and Texas Instruments opamps are available everywhere. I buy them from Digikey and Newark. Newark has recently been bought by Farnell who have warehouses all over the world. Go to their website and click on the flag of your country or a neighbouring country. The very...
  16. audioguru2

    0-30V Stabilized Power Supply

    Your meter might need a completely separate supply with its own power transformer and filtering. A 741 opamp has a design that is 47 years old and it will not work in the improved circuit. It might work in the original Greek circuit or the Chinese copy of the circuit if the transformer voltage...
  17. audioguru2

    0-30V Stabilized Power Supply

    ebay cannot even spell the word "meter" correctly, they say it is a motor. Their very cheap meter might not be able to measure its own supply, instead it might need a separate power supply or battery like most meters. The Greek kit and the Chinese one cannot produce 30VDC at 3A and its main...
  18. audioguru2

    0-30 VDC Stabilized Power Supply 0.002-3 A

    The kit from Banggood is a copy of the original kit from Greece with a couple of parts changed. It will not produce 30VDC at 3A and the TL081 opamps will have a total supply voltage higher than they are allowed when the load current is low. The single output transistor will get much too hot when...
  19. audioguru2

    IC Issue

    I buy food at a market. I buy the newest electronic ICs from an electronics parts distributor like Digikey. Or you can go to the website of Farnell and click on the flag of a country nearest you. If I order online or by phone in an order before 8:00PM then it is delivered to me the next morning...
  20. audioguru2

    Watt of LED

    An LED sets its own voltage. A red one is about 1.8V to about 2.0V. A blue or white one is about 3.2V to about 3.6V and they are all different unless they were all measured and grouped. The brightness of an LED is controlled by adjusting its current, not its voltage. To avoid burning out an LED...
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