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  1. audioguru2

    a very simple FM Tx

    Hi Walid, That is an extremely simple FM transmitter circuit. Did you make it? How is its performance? 1) The 1nF cap makes the transistor a common-base amplifier at radio frequencies where the emitter is its input and the collector is its output. 2) The coil and capacitor in parallel with it...
  2. audioguru2

    Electronic Stethoscope 2

    The electret microphone is polarized so its terminal that is connected to its metal case is ground. The project needs a two-wires electret microphone from a toy or from a telephone. A three-wires electret microphone needs a different circuit. Maybe you have a condenser microphone. It is...
  3. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Does it work? Does it get really hot? It will be difficult to measure its square-wave output voltage accurately with a meter that doesn't measure AC with "true RMS" circuitry. Please post its schematic so we can see "what makes it tick".
  4. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Hi Sasi, How are you? What do you think about Steven's 50% efficient square-wave inverter? What do you think about the recent "deletion and corrections" that were made to our 500W inverter project?: http://www.electronics-lab.com/projects/power/033/index.html
  5. audioguru2

    220 volts Versus 120 volts

    Hi Don, I am in Canada where we have both 120VAC and 240VAC in our homes. Most things work with 120VAC but high power appliances like the stove, air conditioning and clothes dryer use 240V. Your halogen light bulb is 22.8V or 24V and they are only 5% different so either bulb will work fine. The...
  6. audioguru2

    Electronic Stethoscope

    Hi Mahesh, The input to the electronic stethoscope project is the low frequency audio sound of heartbeats. The electret microphone picks the sound up and the circuit filters out background sounds and amplifies the heartbeat sound.
  7. audioguru2

    FM frequency

    To change the frequencies of your FM radio you need to know how many RF tuned circuits it has that need to be changed. It has an input tuned circuit or two plus an RF oscillator tuned circuit. After increasing their frequencies then they must be aligned for matching across the whole frequency...
  8. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Hee, hee. ;D ;D 120W input makes only 60W to 70W output. Nearly half of the input power makes heat. No schematic?
  9. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Welcome back, Steven. ;D We need to know the continuous power rating of your new inverter. Also please attach its schematic and parts list. It looks like a two transistor multivibrator driving the output transistors. Its output is probably a square-wave. It will be interesting to see if and...
  10. audioguru2

    3-Channel Mixer

    The transistor in the mixer project doesn't have any negative feedback to cope with a transistor that could have a current gain of 200 or 800 or anywhere in between. Look at any transistor design course and it will show transistor amplifier circuits with an emitter resistor or with the base...
  11. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    You need to study about transformers. The size of the core is determined by the frequency and amount of magnetic flux it can have without saturating. You need a high flux to have a high power. High power also requires thick low resistance wire. The number of turns for the primary winding...
  12. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    The transformer needs to be big for it to have a high power rating because the mains frequency is very low. The turns ratio between the primary and secondary determines the output voltage.
  13. audioguru2

    what should i do about computer rf emissions?

    People still use old AM radios? An AM radio is an interference detector.
  14. audioguru2

    FM frequency

    Before you wanted to modify a radio to higher frequencies. Now you want to modify a transmitter to higher frequencies. Both? Why? The site you posted talks about all the RF tuned circuits that need to be changed, then re-aligned. At least two in the radio and at least one in the transmitter...
  15. audioguru2

    3-Channel Mixer

    Hi Rory, Welcome to our forum. ;D That mixer circuit is one of the worst circuits that I have seen! It is too simple to work properly. I used the extremely old BC109 transistor about 40 years ago in my first job at Philips. Its current gain has a very wide range of values from 200 to 800. The...
  16. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi BRNewbie, Since the value of your R7 is 1000 times too high, many parts are affected. Correct it and maybe your project will have an output voltage from 0V to about 25V with a max current of 1.5A.
  17. audioguru2

    CD4049 switching failing to switch

    I must be getting old because my car radio remembers more about what my wife likes than I can remember. ;D
  18. audioguru2

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

    Your temporary wires are too long and have too much resistance to properly measure the regulation of your circuit. A wire with only 0.002 ohms will create a voltage drop of 10mV at 5A. I think your "spikes" are ripple since the U2 opamp is saturated up at the positive supply. Transformer...
  19. audioguru2

    FM frequency

    Hi Ante, Of course a wideband FM receiver won't work on narrow band AM airplane transmissions but a down converter will allow him to hear what happens when the wrong type of radio is used. Many years ago I made a "crystal radio" that worked very well at the airport. It had a single tuned...
  20. audioguru2

    CD4049 switching failing to switch

    Hi Wellington, The output current of the CD4049 is not symmetrical. It sinks a lot more current than it sources. I would use a CD4069 hex inverter that has a perfectly symmetrical output current. The value of R24 should be much lower than the value of R23 for the alternate-action circuit to be...
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