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  1. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    Kobus, You almost got it all. If you want your Power Supply to provide up to 5A at any output voltage from 0V (dead short) to 30V, then I will update and correct your list: 1) Transformer: 30VAC, 7.5A, 225VA. 2) R2 & R3 = 1/2W. R7 = 0.27 ohms, 15 or 20W. R1 = 3 or 4W. R14 = 1.2K...
  2. audioguru2

    Electronic Stethoscope

    Tomah, That is wonderful that your project works well. ;D You are clever to change it so that U5 has a proper negative supply voltage. Try connecting the junction of C3 and R7 to pin 6 of U2, and change C2 to 4.7uF, with its + terminal towards the microphone. Please let us know the results...
  3. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Guys, I just realised that there is an error in the schematic and PCB for this project: The emitter of Q1 should be connected to 0V, not to the negative output of the rectifiers as it is now. While the circuit is operating, Q1 should be turned-off, since it is used only to quickly reduce the...
  4. audioguru2

    0-30 Vdc Stabilized Power Supply

    Kobus, Let's keep this thread for modifications to the original 3A power supply to make it reliably meet its specs. I am replying to your other post to modify it for 5A output. ::)
  5. audioguru2

    Beginners Transistor Help

    Kevin, A transistor is usually used at a power level that is much less than half of its maximum power rating, to avoid excessive heat and uneccessarily high power supply current. However, to obtain its maximum dynamic range between cutoff and saturation, a transistor is biased so that its...
  6. audioguru2

    Beginners Transistor Help

    Electrodoc, I am sorry, but those statements are either very confusing or just plain backwards. Just remember that with the emitter as the reference, an NPN transistor needs a Positive voltage for its base and collector, and a PNP transistor needs a Negative voltage for its base and collector...
  7. audioguru2

    My new headphone amp :-D

    Hi Wellington, I am glad that your headphones amp project, "Headbanger", works well. It is interesting that its author used additional negative feedback to reduce distortion and noise of the LM386, and to extend the bass response much lower than the rather small output cap would normally produce.
  8. audioguru2

    was Re:Ir-remote Now is: Op Amp discussion

    Kevin, You keep thinking that an opamp is a transistor. They are not the same. An opamp is a complete amplifier with a voltage gain of about 200,000, a low-impedance symmetrical push-pull output and a high-impedance differential input. It doesn't need a resistor at its output to a supply...
  9. audioguru2

    was Re:Ir-remote Now is: Op Amp discussion

    Kevin, I don't understand you. You didn't attach a sketch of whatever you are talking about. In my last reply, I posted the data sheet for a 741 opamp. It doesn't have the diodes that you are talking about, and it uses transistor current sources instead of the collector resistors that you are...
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Capricious, You can use the 12V secondary for a 12VDC fan if you use 4 rectifiers. Put a filter cap and a series resistor to the fan if it buzzes. Thermal grease is about 0.7 Kelvin/W. I don't know which insulator that you are using, it should be rated. For the project to operate with 12VAC...
  11. audioguru2

    Capacitor

    Quantum, I use a spring-activated desoldering tool for removing a few components, slowly. With my automatic temperature controlled soldering iron, I cause very little damage. I have seen soldering iron tips shaped like an 8, 14 or 16 pin DIL, for removing ICs very safely and quickly.
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Gosi, Welcome to our forum. I agree with you that a single 2N3055 has a serious thermal problem in this project. Your 24VAC, 1A transformer is rated for a maximum power output of only 24VA. Since it must supply a peak voltage of 34V into the rectifiers at a high momentary current, then it can...
  13. audioguru2

    Servo Throttle Control

    Mbedford, Cruise control for your boat? Keep the pot and electronics dry. You could keep it very simple by using only the throttle lever/pot with feedback from the RPM gauge, to set the RPMs. If you slowly move the lever, then the revs will slowly follow. But if you jerk the lever forward, then...
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    Capricious, The author of this project used a pretty big heatsink. He even used a clip thingy on Q2. He didn't show his huge fan. Is his fan used for cooling, or for blowing away the smoke? (Or for blowing away your hair that you tear-out when the transistors melt) See my reply in your other...
  15. audioguru2

    What is K/W from heat sinks?

    Capricious, That's right. A heatsink that is rated at 2.4 K/W increases its temp 2.4 degrees Kelvin for each Watt that it must dissipate, in standing calm air. This is called its thermal resistance. You use this value to determine if the heatsink is large enough or whether it will need forced...
  16. audioguru2

    Problem with mini amp circuit

    Wellington, The Mini-box 2W amp is much better than the other simple amp. I think that its capacitor C2's polarity is backwards.
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

    Capricious, 1) A pull out and put in replacement for the TL081 (change all 3) is either the MC34071AP or the TLE2141CP. Both are rated for 44V max. 2) Your project has heat problems: a) The 2N3055 can dissipate 115W if you can somehow keep its case at no more than 25 degrees C. Its junction temp...
  18. audioguru2

    Amplify

    Quantum, You can search the internet using a search engine such as www.google.com, or click on the "search www" under my signature, and enter LM386 in the box. The LM386 data sheet has many schematics for its applications. The data sheet is here: http://www.national.com/ds/LM/LM386.pdf
  19. audioguru2

    Capacitor

    Quantum, The heat of soldering does not affect a capacitor's performance if the soldering is done quickly and correctly. Even a polyester capacitor is not damaged (polyester melts at a low temperature) by soldering because its wires are made of a material that does not conduct heat well.
  20. audioguru2

    was Re:Ir-remote Now is: Op Amp discussion

    Kevin, 18mA of load current is a lot for most opamps, especially when the load connects to a negative voltage, instead of to ground as is usual. You don't say which opamp, but a good old 741 is guaranteed to swing its output to only 10V with a 2K load to ground, when using a +, - 15V supply...
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