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  1. audioguru2

    led powered by a/c How To?

    The circuit uses the reactance of the capacitor to efficiently reduce the current, thefore it has a high AC voltage across it. Each half-cycle of the mains, the voltage across the capacitor reverses its polarity. Polarized electrolytic capacitors conduct a high leakage current with reversed...
  2. audioguru2

    Power Supply - looking for 200pf capacitor

    The project's photo shows a metalized plastic film capacitor for C5. They aren't made as 0.02uF but are made as 220nF which is close enough for a simple supply bypass capacitor.
  3. audioguru2

    Quick AC question

    Hi Alun, In North America, many appliances and electrical cords have only two wires, live and neutral. There is not a ground wire so their switch is DPDT to cutoff both wires in case the receptacle was wired wrong. Electricians are human (I think?) and make mistakes. I was in a building under...
  4. audioguru2

    0-30 Vdc Stabilized Power Supply

    OK. Comparator ICs don't have built-in frequency compensation so they can have gain at high frequencies. Therefore they never use negative feedback with a resistor or integrating capacitor in order to avoid oscillation. Usually comparator circuits use a small amount of positive feedback to avoid...
  5. audioguru2

    Universal battery charger

    The threshold voltage is adjusted with the pot. The opamp is definately used as a comparator. The 820k resistor provides a little positive feedback for snap-action switching which avoids oscillation at the threshold. The slow opamp that is used as a comparator probably won't oscillate but at the...
  6. audioguru2

    motor driver problem

    Didn't you look at the datasheet for the TA7259 driver IC? http://www.datasheetarchive.com/semiconductors/download.php?Datasheet=2050111
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Indulis, Welcome to our forum. ;D You are correct by stating that U3 is not being used as a true comparator. It is using its inputs to compare the voltage across R7 that is caused by load current, with the voltage from the current-setting pot. Then it uses its internal gain of a few hundred...
  8. audioguru2

    Quick AC question

  9. audioguru2

    Bass Extender

    Nope. There isn't much to see. Two Acoustic Research speakers about 40 years old (two-way, 8" woofers, sealed cabinets) and some ported two-way speakers I made that have 8" woofers. I have an 18 years old Yamaha stereo receiver with "Low Impedance Drive Capability"  that produces about 70 real...
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Smit, The current regulator works by using U3 as a comparator to compare the voltage across R7 caused by load current, with the setting of the current pot P2 and causing the output voltage to be reduced through D9 to maintain the set current. Since the reference voltage is +11.2V, the output...
  11. audioguru2

    Bass Extender

    Hi Ante, I have Microsoft IE6 browser. If I go directly to Silicon Chip Online to look at a project, I get only the 1st page then a begging-for-payment page like you get. But if I enter the project's name in Google, then the 1st link is to the entire article. Many other people get complete SC...
  12. audioguru2

    amp. problem

    Good, you fixed it! ;D
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Zama, Q1 is supposed to be turned off when the project is operating. It turns on only when the mains is turned off. Q1 must conduct the short-circuit current of U2 which could be 20mA if your project's U2 is strong. If the project's output voltage is set to 30V when the mains is turned off...
  14. audioguru2

    time beeper

    Hi Alun, The internal resistance of the battery cells is also next to nothing. For a fresh alkaline AA cell it is only 146 milli-ohms, so at 167mA on the graph it has a voltage drop of only 24mV. The lithium cell has such a low internal resistance that it isn't even mentioned. I've measured...
  15. audioguru2

    Resistor wattage

    Resistors are very cheap. I derate them to keep them cooler and reduce any change of their value caused by heat.
  16. audioguru2

    Bass Extender

    Google looking at Silicon Chip projects work OK for me every time. They must like my cookies or something.
  17. audioguru2

    Resistor wattage

    Yes, but resistors operated at their max rating are extremely hot, enough to melt plastic or char a pcb. In circuits I design I never allow a resistor to operate at more than 0.75 of its max power rating.
  18. audioguru2

    Quick AC question

    If it plugs-in both directions then you should use a double-pole switch to make certain that the live wire is switched.
  19. audioguru2

    Electronically controlled 12V 75W lamp

    I'm very close to Toronto, Canada. ;D
  20. audioguru2

    Electronically controlled 12V 75W lamp

    Hi Simian, The battery cell looks like a fully-filled C size. Here, Energizer puts a little AA size battery cell in their C cells and rate it at 2500mA/hrs. ;D
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