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  1. audioguru2

    problem with a rectifier

    Kevin, A rectifier with a filter cap isn't an RC low pass filter. The cap simply charges very quickly through the low resistance of the transformer and extremely low impedance of the rectifier, then discharges into the load between charge pulses from the rectifier. The exponentially dropping...
  2. audioguru2

    problem with a rectifier

    Kevin, The size and impedance of the rectifier diodes don't affect the ripple. The size (value) of the filter cap and amount of load current affect the ripple. ::) Hi Shekhar, Maybe you have a high-power radio or TV transmitter nearby that is picked-up by your wiring and showing on your DMM...
  3. audioguru2

    capacitance meter

    Kevin, When the 555's output goes low, the cap charges through the upper diode and the resistor. The lower diode is reverse-biased. When the 555's output goes high, the upper terminal of the cap is driven above the supply voltage due to its charge (see the meter's polarity?), the upper diode is...
  4. audioguru2

    6V Ultra-Bright Chaser

    Hi Alun, I spec LEDs that are less than 2V for my 3V project, usually red but I have also used orange and yellow. I spec (about) 3.2V LEDs for my 6V project, usually blue, ultra-bright green or white. Of course 3.2V LEDs won't work in the 3V project, especially when the battery runs-down to 2V...
  5. audioguru2

    Transformer Power Rating

    Hi Atheos, Since each amp will provide 140W into 4 ohms and 70W to heat itself, a stereo amp will require 420VA from the transformer. Therefore the transformer must be also rated for at least 420VA, which when divided by 56V equals 7.5A. If you used a transformer with two 28V secondary windings...
  6. audioguru2

    Transformer Power Rating

    Hi Kevin, 8A is the transformer's maximum continuous RMS rating for its output at "normal" ambient temperature and not totally enclosed. Transformers are not rated for "average" current but for your information, the average voltage or current of a sine-wave is 90.099 percent of its RMS value...
  7. audioguru2

    6V Ultra-Bright Chaser

    Hi Guys, I have been making a bunch of this project: http://www.electronics-lab.com/projects/games/004/index.html hasn't anyone else? I have also been converting all my 3V chasers into this circuit, modified for 3V as in the project's text, they look more interesting and their battery lasts...
  8. audioguru2

    Transformer Power Rating

    Hi Atheos, I don't see how that amplifier can provide 100W continuously into 8 ohms with low distortion when using only a dual 40V supply. 100W into 8 ohms requires a sine-wave of 80V peak-to-peak. The amplifier's Q10, output emitter followers and emitter resistors all create a voltage loss so...
  9. audioguru2

    Newb needs help!

    Hi Alun, Many of those little transistors have a maximum rating of only 100mA. Many also have a very low current gain of only 40 with a 288mA collector current, so the value of your base resistor is much too high. I don't know if the microcontroller can output 5mA to drive the base of a...
  10. audioguru2

    Electronic Eavesdropping Devices Detector

    Hi Jason, Maybe the VCO isn't working properly and doesn't change the pitch of the tone with changes in signal strength. Maybe your cell phone operates at a radio frequency higher than this project can detect. Try driving it closer and closer to a radio or TV transmitter with its sensitivity...
  11. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Giova, When you tried a 100K pot your project showed that it can produce nearly 1A when forced. Check C8. Maybe it is broken or poorly soldered and is causing U3 to oscillate. Also check the parts for the negative supply. The voltage across D7 should always be about minus 5.6V.
  12. audioguru2

    Dome Lamp Dimmer

    I don't think a speaker has much inductance when compared to the high inductance of a motor.
  13. audioguru2

    Dome Lamp Dimmer

    Poor radio with an inductive load.
  14. audioguru2

    How much does cost electronics parts?

    Hi Hyaku, Anything that is new technology is expensive. Red LEDs have been around for many years and therefore are cheap now. If you buy 10 blue LEDs, ask for a quantity discount. You should get them for about $8.00 or get 2 more free. Small diodes used to be $1.00 but are $.10 each now...
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Giova, With the current pot turned up and the output voltage set to about 22V or less, the output should be able to provide 3A to a load that draws 3A at that voltage. Is the transformer rated for 3A? The current regulation indicator LED should not light. Maybe your load draws only 0.08A at...
  16. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Dex, Welcome to our forum. Your schematic looks fine. 1) Using TL081 opamps, you shouldn't use a 30VAC transformer so the project's output voltage won't reach 30VDC with a load. 2) You are correct, the emitter of T1 should connect to the negative side of C1. 3) You are also correct, RV1...
  17. audioguru2

    LM78XX & LM79XX questions

    Hi Autir, He, he. ;D That's right, the electrolytic will leak or just "dry out" in a few years or many years depending on its quality. Then the regulator will go crazy without an input cap and maybe destroy your load.
  18. audioguru2

    transformer questions

    Hi Autil, A transformer is designed to output its rated RMS voltage with its rated load current. Since its windings have resistance they cause a voltage drop when current flows through them. The designers have adjusted the output voltage so that is is what it should be when the voltage drop...
  19. audioguru2

    LM78XX & LM79XX questions

    Hi Autir, I have used BC Components (used to be made by Philips and Siemens) 370 series polyester caps for audio coupling for many years. "They work better" than ceramic or electrolytic for audio because they have very low distortion. For a power supply, distortion doesn't matter and since the...
  20. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Giova, Welcome to our forum. Did you use the original project's schematic? Check R7, R21, R17, R18, P2 and U3. They regulate the output current.
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