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  1. audioguru2

    class of amplifier

    I think all circuits like that should have emitter resistors to avoid thermal runaway. This one gets away with it because of its low output power. Its gain isn't nearly as high as an opamp as seen by its fairly high distortion. An opamp has a fairly high open-loop noise and a distortion of maybe...
  2. audioguru2

    class of amplifier

    Hi Alun, Good, but chunky transistors have less gain so Ibias will need to be higher. Yes, Rbias is in a voltage divider with Rf. Have you seen the high cost of those things? All they are is a FET with a gate-source short like you have now. Try a couple of bootstrap resistors with a cap...
  3. audioguru2

    Electric assist bike

    PWM controls motor speed by changing the duty-cycle of the full voltage pulses applied to the motor. The motor's average current is determined by its load and you probably need a tachometer to adjust the PWM for it to maintain a speed with varying loads like hills. The PWM needs a throttle to...
  4. audioguru2

    Pb-free soldering

    The beaurocrats are worried about lead contaminated circuit boards littering everywhere like gum wrappers. Haven't you seen how many people discard circuit boards on streets and sidewalks? ;D
  5. audioguru2

    class of amplifier

    Hi Miles, Here's another class to add to your collection.  ;D Class-H. It switches the power supply voltage of an amp between a low voltage for good efficiency at low power output, and a higher supply voltage during loud peaks in the output. This Philips car amp IC even has a built-in voltage...
  6. audioguru2

    class of amplifier

    Hi Alun, You are severely straining your poor little output transistors that have an absolute max current rating of only 100mA. To get 6Vp-p into your 8 ohm load, each output transistor will have a peak collector (emitter) current of 375mA. You are lucky they survived and their hFE drops like a...
  7. audioguru2

    Portable CD Player Adapter For Car

    A Discman doesn't have inputs so doesn't have an input resistance. It just needs a stable supply voltage with enough current for it to operate properly. If the voltage regulator's voltage is correct for your Discman, why not use it? If it needs a voltage that is not available in a fixed...
  8. audioguru2

    RC time constant

    The cutoff frequency of an RC filter is calculated as: 1 divided by 2 pi RC. I make it simpler by rounding it off a bit: 0.16 divided by RC. R is in ohms and C is in Farads. You must physically swap the parts to change from a lowpass to a highpass filter and vice-versa. In a lowpass filter, the...
  9. audioguru2

    Portable CD Player Adapter For Car

    Hi Esh, Welcome to our forum.  ;D Please attach the circuit's schematic to your post or provide a link to it so we can see which capacitors you are talking about. A voltage regulator powers a circuit with a fixed constant voltage that doesn't change when the input voltage changes or when the...
  10. audioguru2

    class of amplifier

    Hi Alun, Ibias needs to have a low voltage drop for it to turn-on Tr3 fully when the output swings high. Frequently a bootstrap arrangement drives Ibias higher than the supply voltage (with a capacitor from the output) for a good output swing. Maybe Ibias has too much voltage drop or maybe you...
  11. audioguru2

    class of amplifier

    Opamps usually operate their output transistors in class-AB for low distortion. If you look at the spec's of a low-power opamp like the LM324 or LM358, you will see that they operate their output transistors with a very low idle current in class-B, which causes crossover distortion. Their...
  12. audioguru2

    RC time constant

    No, with a very low RC the circuit is not a lowpass filter, it is still a highpass but its cutoff frequency is even higher.
  13. audioguru2

    class of amplifier

    You can design a transistor amplifier to operate in whichever class you want. You can purchase a class-A audio amplifier which will create a lot of heat but have a fairly low output power, or the usual class-AB one which operates much cooler and has a high output power. 
  14. audioguru2

    My girlfriend is getting into electronics

    Whenever I see 10 labourers, one is doing all the work and the others are just watching or supervising him.  ;D
  15. audioguru2

    EYE SIGHT SENSOR

    A sensor could easily detect the X-ray vision of Superman, but usually our vision doesn't emit anything for a sensor to detect.
  16. audioguru2

    RC time constant

    Kevin, Are you talking about an RC lowpass filter? It attenuates high frequencies gradually. If you select a long RC time constant for better attenuation, then it might take too much time to charge and a multiple-stage filter would be best. You contradict yourself when you talk about the...
  17. audioguru2

    Increasing the range of Transmitter

    Hi Monkeyman, Great, it goes much farther (further?)! ;D The amplifier probably has as much output as it can, so another amplifier would just overload. Besides, even now you might be visited by the RF cops.  ;D
  18. audioguru2

    Electronic Stethoscope

    Hi Dazza, The LM358 has a minimum output current rating of only 10mA, typically 20mA. If your LM386 in the electronic stethoscope is driving two paralleled 32 ohm earphones to full output, it would draw about 72mA plus a few more mA for the opamps. The LM358 is a low power device but an MC1458...
  19. audioguru2

    mp3 player from hardisk

    That MP3 player module might be out of date. It uses the same SIMM memory as in my old 486 computer.
  20. audioguru2

    Additional Information

    Hi Nab, For the Dancing LEDs project, if you remove C2 then IC1A will be a follower with a gain of 1 instead of the desired gain of 101. If you bypass C2 so that R4 connects to ground, the output voltage of IC1A will be saturated against the positive supply. An opamp with negative feedback will...
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