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  1. audioguru2

    transistors

    No, the gain is only 3dB because the reactance of a capacitor causes phase-shift. If the capacitor was a resistor with the same value as the capacitor's reactance then the gain would increase 6dB. ;D
  2. audioguru2

    TRANSISTOR ATTENUATOR?

    Sorry Kevin, Your circuit is a nightmare. Only a single resistor is a positive supply for 2 transistors. If the input voltage becomes high enough then the PNP transistor's base-emitter junction will become reverse-biased beyond its ratings (only 5V to 7V) and have avalanche breakdown.
  3. audioguru2

    transistors

    Hi Bjorn, You almost got it right. The gain with RE bypassed is RC/Re. ;D You can also use the emitter resistor's bypass cap as a treble-boost highpass filter. The frequency at which the capacitor's reactance equals the value of the emitter resistor the gain will be up 3dB, with 20dB for each...
  4. audioguru2

    Intercom station design calculation with LM386

    Hi Hilario, Welcome to our forum. ;D The LM386 is a low power audio amp with enough gain to be an intercom station. If you use two stations connected together then they will make acoustical feedback howling, unless you use a manual push-to-talk switch or an automatic circuit to detect a voice...
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Vedran, The transformer will be seriously overloaded unless you change the value of R7 to 2.2 ohms/2W to limit the project's max output current to about 0.6A. Change R11 to 39k to limit the max output voltage to about 27V because the output will have a high ripple when it is set to voltages...
  6. audioguru2

    Laser questions

    Hi Greek, There are two powering circuits. The upper one with a regulated current adjustable supply with a 100 ohm current limiting resistor and the lower one with a fixed 10V supply, a 100 ohm current limiting resistor and a 100 ohm pot. Which circuit did you use? ??? If you used the circuit...
  7. audioguru2

    Novice help required - reducing voltage

    Hi Detrjo, Welcome to our forum. ;D You can't use a resistor to reduce voltage for a product unless the product's current draw is always the same. Surely your 2-way radio draws a high current when it transmits or plays voices loudly, and a low current the rest of the time. Therefore if you used...
  8. audioguru2

    Charging a 9V rechargable battery using two 9V dc Motors

    Hi FlipFlop, Is your 9V battery a little "transistor radio" size, which is really 7.2V and is it a 120mA/hr Ni-Cad or a 150mA/hr Mi-MH? Energizer recommends a max charging current of only 24mA and 30mA for them, so they will take up to about 6 hours to fully charge. If your "generators" have...
  9. audioguru2

    HELP! project abt DC power supply.

    Hi Ante, A dictionary won't help you understand what these kids are saying. Their teacher should teach them English and grammar before teaching them that power supplies have a rated output current. ;D ;D
  10. audioguru2

    LED questions

    Same thing.
  11. audioguru2

    LED questions

    The remote for my TV and digital video recorder works pretty far away no matter where I point it, even if I point it at the white closet doors behind me. So it must transmit IR in a fairly wide angle. The 3-pin IR receiver IC responds with great sensitivity to modulated IR and has automatic gain...
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    Yeah, this site has problems. It was down for hours then came back and gave me a bunch of phoney e-mails about people replying to my posts a few days ago. But the new e-mails are copies of ones I received a few days ago.
  13. audioguru2

    Very low power FM transmitter discussion

    Hi Walid, The transistor is a common-base RF oscillator. Its output is the collector and its input is its emitter. You could say that the transistor operates as common-collector (emitter-follower) for audio frequencies because changing its base voltage changes the voltage between its collector...
  14. audioguru2

    Charging a 9V rechargable battery using two 9V dc Motors

    Hi FipFlop, Having a DC electric motor drive a DC generator wastes a lot of power as heat in the motor and generator. What is the power supply and why can't it be used to charge the 9V battery though a current-limiting resistor?
  15. audioguru2

    opamp won't output zero

    It won't be repeatable because each transistor would have a different Re and therefore would have a different gain. You would need to select the transistor from a bucket full of them, or tailor the collector resistor to match each transistor. Also, the distortion would be excessive without...
  16. audioguru2

    Very low power FM transmitter discussion

    Hi Walid, Did the FM transmitter work? I think the value of the 22k supply/load resistor for the electret mic is much too high with only a 1.5V supply. Most electret mics operate with a 9V supply, a 10k supply/load resistor and draw about 500uA. I think it would work a lot better with a 2.2k...
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Zeppelin, I keep getting notification of replies from you that don't exist and get instant messages from you that I can't reply to, about the high cost of parts for this project. This is what I recommend for a 3A supply: 0-30V_Mod_parts_list.txt
  18. audioguru2

    Transistor Biasing Problem

    Hi Geo, The alpha, beta and Vbe of a transistor change with temperature and are different between two transistors with the same part number. The only information about the transistor is its Vbe, so its alpha, beta, temperature and very accurate voltages and currents are impossible to calculate...
  19. audioguru2

    Speakers

    Hi Steve, I took a standard Sallen-Key highpass filter with a cutoff frequency of about 30Hz, made it for a single supply and made the feedback adjustment of its Q or damping, adjustable. When the slider of the pot is lowered on the schematic then bass frequencies are boosted around its cutoff...
  20. audioguru2

    TRANSISTOR ATTENUATOR?

    Kevin, I don't know what your numbers are supposed to be about. Aren't you making a Cascode Amplifier? It doesn't need a collector resistor for its lower transistor. The voltage gain of the lower transistor is only about 1 becase its high impedance collector is severely loaded down by the very...
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