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  1. audioguru2

    FM WAVE PROPAGATION

    Hi Prateek, You shouldn't blindly choose a preamp for the FM transmitter. It should operate properly over the circuit's power supply voltage range. It should have the required amount of gain and have pre-emphasis, low distortion and a wide frequency response to sound right. Look at the preamp in...
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    It does have a few bugs, but the main one is that the little 2N2219 vapourises when it is overloaded. Then there is the overloaded transformer that doesn't have enough output voltage, etc. I wonder what the new bug is.
  3. audioguru2

    negative supply

    Hi Rehanessa, "Completely isolated" means having its own transformer winding and rectifier and nowhere in its circuit is grounded.
  4. audioguru2

    Electronic Stethoscope 2

    Hi again Loveguru, I just finished measuring the output impedance of my electret mic with its 10K power-feed/load resistor. I measured 3123 ohms. Yours will probably be different. Therefore the low frequency cutoff including the project's 2.2K R2 and 4.7uF C2 is 6.4Hz. The response at 32Hz will...
  5. audioguru2

    Electronic Stethoscope 2

    Hi Loveguru, Don't use a HPF before U1a and don't use an audio bandpass filter. You need the frequency response to go very low. You are correct that heartbeats repeat about once per second when slow. But the sound is low frequency audio, about 20Hz to 30Hz like a bass drum. I don't know what is...
  6. audioguru2

    FM WAVE PROPAGATION

    Hi Prateek, You can assume that the transmitter is 50% efficient, then measure its operating current and voltage, multiply them to calculate total power used, and divide the total power by 2. If your transmitter doesn't have an output tuned circuit tuned to its operating RF frequency, then it...
  7. audioguru2

    VOX is not working - any help?

    Hi Con, Your circuit is easily modified to use your electret microphone. Post its schematic and we will show you how.
  8. audioguru2

    wireless transmitter

    Hi Alun, Electret microphones and phantom-powered condenser mics have about the same low-level output as dynamic coil and magnet mics, about 14mV p-p at a distance of 10cm with a normal speaking voice. Since the FM transmitter circuits need an audio input of about 400mV p-p, my mic preamp has a...
  9. audioguru2

    Electronic Stethoscope 2

    Hi Loveguru, I am glad to help you. 1) A High Pass Filter passes high frequencies down to its cutoff frequency and attenuates lower frequencies. A LPF does the opposite. 2) An amplifier can oscillate at a low frequency if it doesn't have adequate supply bypassing in stages, to compensate for the...
  10. audioguru2

    FM WAVE PROPAGATION

    Hi Prateek, You should find out the rules and regulations of transmitters in your country. In Canada, anyone can transmit on the FM band with a power up to 100mW as long as they don't cause complaints about interference, profanity and stuff like that. You will be in big trouble if you transmit...
  11. audioguru2

    FM WAVE PROPAGATION

    Hi Prateek, Both very simple FM transmitters don't have an FM modulator. Their preamp actually AM modulates the FM oscillator. Since the oscillator transistor has its amplitude changing, its capacitance also changes, creating FM. Maybe you mean I should cutoff extremely high audio frequencies...
  12. audioguru2

    wireless transmitter

    Hi Alun, Your "preamp" won't have enough gain, only 4.5 if you're lucky. I improved and reported my test of the preamp section of an FM transmitter here:
  13. audioguru2

    FM WAVE PROPAGATION

    Hi Prateek, Make an FM transmitter! 1) The simple one is just a toy. Its preamp is a thermometer and battery voltage indicator. I tried it. a) With a new 9V battery and a transistor with a typical hFE (300) or more, the preamp transistor is saturated and doesn't work, but works with a battery...
  14. audioguru2

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

    Hello, "your majesty", Your transformer is good for this improved project. It will allow the project to deliver up to 3.5ADC at the transformer's 150VA limit. You would need only two 2N3055 transistors instead of three that are needed for a 5A output. Your 150VA transformer would produce a peak...
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi DJF, Welcome to our forum. We have been saying here that the 2N2219 is too flimsy for this project. Use a strong TIP31A mounted on a heatsink. I don't know why U1 is burning. It is the voltage reference that doesn't have much load, operates within its supply voltage rating (unlike the other 2...
  16. audioguru2

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

    Hi King, your majesty, Welcome to our forum. To get a properly regulated 30VDC at 5A out of this project the transformer must be rated to produce 30VAC at 7.5A which is 225VA. Of course, that is its voltage measurement when it is loaded with a 7.5A AC load. The recifier bridge and filter...
  17. audioguru2

    again, microphone input high school project

    Hi Zgnoh, Many elecrical appliances are earthed for safety. Big radio transmitters are earthed so that their antennas work correctly. But your project doesn't have to have its ground common connection earthed. When you connect something to the earth you connect it to a cold water pipe where the...
  18. audioguru2

    negative supply

    Hi Rehanessa, You can't use a single transformer winding when you put two regulated power supply circuits in series because the winding will never produce a negative voltage with full wave rectifiers. You could do it with half wave rectifiers: 1) use one wire of the transformer as the common...
  19. audioguru2

    VOX is not working - any help?

    Hi Con, On your picture, it looks like an electret microphone, but the circuit doesn't have any way to power it. The circuit is probably designed for a dynamic microphone that has a coil and magnet to generate a tiny amount of electricity when it hears sound. When you used a piece of wire, it...
  20. audioguru2

    Electronic Stethoscope 2

    Hi Loveguru, I'm glad and relieved that you finally got your project to work very well. 1) A 47K pot will work exactly the same as a 10K or even a 2.2K pot, no change in volume. Pots don't amplify, and it certainly won't load-down the very low output impedance of U1b unless it was 2K ohms or...
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