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  1. audioguru2

    Class A amplifier Formulae help!!!

    Hi Shaiq, Transistor amplifiers have a very high amount of distortion without negative feedback. The 1st circuit I simulated had a voltage gain of about 120 and distortion of about 10%. The distortion is much higher when its levels are increased. I removed the capacitor across the emitter...
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    I haven't made an opamp since about 40 years ago. I don't know if a Bryston discrete opamp has a low input offset voltage, has a high enough gain and frequency compensation and enough input and output voltage range for this project. The Bryston opamp might oscillate with the very low closed loop...
  3. audioguru2

    Class A amplifier Formulae help!!!

    Hi Shaiq, I simulated your 2nd circuit. Because it doesn't have negative feedback and because it has a resistor instead of a current source as its transistor's DC load, it has high distortion that changes its DC bias. This pic shows about 10% distortion on its output. The top part of the...
  4. audioguru2

    Class A amplifier Formulae help!!!

    Hi Shaiq, Please attach a schematic of your class-A amplifier. I don't know if it has an active current-sink and if it is capacitor-coupled to the load resistor.
  5. audioguru2

    Wireless (Radio) Headphones

    The scanning FM "radio" you got as a gift is garbage and I have two that I got for free. They are mono not stereo and are very poor radios. The Dollar Store sells them for $1.00 with two battery cells, earphones and a built-in flashlight. If you buy a small good FM stereo receiver for...
  6. audioguru2

    Wireless (Radio) Headphones

    Hi Asdf, Welcome to our forum. ;D Aren't you getting "transmitter" and "receiver" terms mixed up? You want a stereo radio receiver at the headphones and a stereo radio transmitter at the MP3 player. A small half-decent FM stereo radio receiver is pretty expensive, and so is a small FM stereo...
  7. audioguru2

    reduce handsfree speaker for mic input

    Hi Glytch, Welcome to our forum. ;D All you need is a resistor and a coupling capacitor in series from the few hundred millivolts output to the earphone to the 10mV mic input. The mic input impedance is about 3k ohms so the resistor should have a value of about 30k ohms, and the capacitor can be...
  8. audioguru2

    High Power LED Mood Lamp

    Hi Nefelodamon, Your pcb layout looks good. ;D Did you purchase and receive the Chinese LED? Does it look like it needs a heatsink? The project's author bolted his prototype LED to a metal heatsink.
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    If you connected 48VAC to the circuit then the positive unregulated supply would have been about 69.3VDC, plus the negative 5.6VDC so two of the opamps would have been powered with 74.9VDC. The TL081 opamps have an absolute max voltage rating of only 36VDC. Since the current adjustment pot...
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Len, Welcome to our forum. ;D The schematic in the project is very clear, when you click on it to increase the resolution. It shows where each pin on each IC connects to. If you mixed up some of the pins then maybe the IC is destroyed. Did you substitute any parts? We can help you...
  11. audioguru2

    about electronics eavesdropping devices detector

    Hi Halconbeta, Welcome to our forum. ;D The project is supposed to be sensitive to cell phone frequencies up to 1.9GHz. The very old 2N2708 has no gain above only 700MHz but the BFR90A goes up to 6GHz.
  12. audioguru2

    High Power LED Mood Lamp

    The project will work with a 4.5V regulated supply but the LEDs will operate on much less current and will be dimmer. It is easy to make a 5.0V/500mA regulated supply. Use a 8VDC to 10VDC /500mA unregulated wall-wart adapter and add a 7805 regulator IC with a small heatsink.
  13. audioguru2

    High Power LED Mood Lamp

    A 0.1uF/50V ceramic disc capacitor is fine as a supply bypass capacitor for the project. Do you have a 5.0VDC/500mA regulated power supply for it?
  14. audioguru2

    Inputting a signal to a Two Way Radio

    Hi Shaiq, Just attenuate the output of the 555 with two resistors in a voltage divider to about 10mV and capacitor-couple the reduced signal to the electret mic. Remove the electret mic and the resistor that powers it if you want. Connect two wires to the speaker and feed the signal to your...
  15. audioguru2

    High Power LED Mood Lamp

    You show 3.7 ohms but 3.9 ohms is a standard value. It will dissipate a max of 400mW so use a 1/2W or 1W resistor which is larger than what you show. The 27 ohms will dissipate 250mW so use a 1/2W resistor. The 15 ohms will dissipate only 100mW so a 1/4W resistor is fine. I recommend adding a...
  16. audioguru2

    Frequency Division

    With a 5V supply, an ordinary Cmos counter is guaranteed to work with a clock frequency as high as only 1.5MHz. A 74HC counter works at much higher frequencies so use a 74HC90 to divide the 4MHz to 400kHz. Feed the 400kHz to two CD4518 dual divide-by-10 counters in series for an output of 40Hz...
  17. audioguru2

    External aerial for FM receiver

    The power cord or earphones cable is made a high impedance at FM requencies with a small inductor in series so the signal isn't shorted, then a small capacitor couples the signal that is picked-up. The small capacitor is frequently just the wires close together side-by-side.
  18. audioguru2

    230V/1000W AC dimmer

    Hi Buddi, I am glad you got it working properly. ;D You adjusted the values of both resistors so that they match the value of the capacitor, and match the threshold voltage of the 4001 IC.
  19. audioguru2

    External aerial for FM receiver

    Most portable FM radios use the earphones cable or a whip aerial. My car radio also has a whip aerial. My home stereo has "rabbit ears" as its FM aerial. My clock radio uses its power cord as its aerial. FM radios need an external aerial. Many AM radios have an internal ferrite bar aerial. Is a...
  20. audioguru2

    230V/1000W AC dimmer

    Hi Ante, It is an interesting backwards dimming circuit. R5 and R6 are in series so their position shouldn't make any difference.
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