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  1. audioguru2

    opamp roll-off

    The base-collector capacitance reduces the gain of a transistor much more than the base-emitter capacitance because base-collector capacitance (Miller capacitance) is negative feedback. The loss of output at high frequencies is because the output cannot slew fast enough. Instead of following...
  2. audioguru2

    0-30V Stabilized Power Supply

    The output of U3 must go up to at least 11.9V so its positive supply must be at least 13.1V. U1 needs a positive supply of at least 12.4V. U2 needs the full positive supply of about 41V. 
  3. audioguru2

    inverter and transformer rating....

    It is a garbage old fashioned circuit. Its output is only 80mA at 200VAC.
  4. audioguru2

    inverter and transformer rating....

    The 2SD313 output transistors operate poorly above 1A but still have some gain at 2A. Then the output from the inverter will be 16W. The 2SC1815 oscillator transistors have a max allowed reverse emitter-base voltage of only 5V but will have avalanche breakdown in this circuit that is missing...
  5. audioguru2

    Portable charger?!

    You can make a simple circuit that produces thousands of volts from an AA cell. But a cell-phone battery has a capacity of about 800mAh and charges at 200mA. A name-brand AA alkaline cell has a capacity of only 1000mAh at a high current output and when its voltage drops to only 1.0V. The...
  6. audioguru2

    Are these two circuits equal?

    The regulators are missing important input and output capacitors that might resonate with the inductors.
  7. audioguru2

    0-30V Stabilized Power Supply

    The MC33171 is low power like an old LM324 but is improved. Therefore its output current is too low, its bandwidth is too low and its slew rate is also too low.
  8. audioguru2

    0-30V Stabilized Power Supply

    The opamps will not affect each other in a quad package but it might overheat.
  9. audioguru2

    Variable duty cycle sawtooth generator

    I think your simulation program did not read all the details on the datasheet for your old opamps.
  10. audioguru2

    Variable duty cycle sawtooth generator

    The datasheet for the old NE5534 says that is is internally frequency compensated for a minimum voltage gain of 3. But you have one as a follower with a voltage gain of 1 so it will probably oscillate or have wild overshoots. Its gain is only about 20 at 1MHz so a triangle-wave will be very curved.
  11. audioguru2

    opamp roll-off

    The 741 opamp and most other opamps have a single RC filter that creates a rolloff at 6dB/octave whhich is 20dB/decade. Depending on its location in the opamp the rolloff capacitor affects the max slew rate. The datasheet for the 741 opamp shows that its max slew rate occurs when its output is...
  12. audioguru2

    Class D audio amplifiers!

    3.5W into 8 ohms is a sine-wave of 15V p-p. With a 16V supply and half-decent Mosfets that each has a voltage loss of 0.5V then 3.5W into 8 ohms is possible. Texas Instruments make class-D audio amplifier ICs. Many are bridged (two amplifiers driving each end of a speaker out-of-phase for...
  13. audioguru2

    Portable Stereo Project: Amp Woes

    An amplifier produces almost double the power into 4 ohms compared to 8 ohms. Double the power is just a little louder. A 0.5W clock radio is pretty loud. My 140W stereo is much louder. At work my demo sound system had 1600W. I tried not to break the windows with it. I am lucky it didn't deafen me.
  14. audioguru2

    Class D audio amplifiers!

    Much less voltage loss so much better efficiency. the power from the amplifier and the power wasted were very low. it has no voltage loss and it operates at a higher frequency. Use 500kHz. The Mosfets have a high input capacitance that makes them switch slowlywhen driven from a Cmos low power...
  15. audioguru2

    Portable Stereo Project: Amp Woes

    With a supply of only 12V its output at clipping is only 1.0W into 8 ohms and 1.75W into 4 ohms. 5W into 8 ohms is 17.9V p-p. The amplifier has an output voltage loss of 4.5V so the supply must be at least 22.4V for 5W into 8 ohms.
  16. audioguru2

    Class D audio amplifiers!

    Your ordinary old 555 has a total output voltage loss of 4V. The output emitter-followers have a loss of 2V. Then the total losses are 6V and since your supply is 16V then the amplifier is only 62.5% efficient. A Cmos 555 has an output current that is too low to drive power transistors. Use...
  17. audioguru2

    0-30V Stabilized Power Supply

    Use Ivan's proposals if you want. The transformer has a listed voltage and has a max allowed current. Multiply them to calculate its max allowed power. The peak voltage of the transformer is multiplied by the max current from the project to calculate the actual power from the transformer. The...
  18. audioguru2

    design an audio amplifier

    You should use a modern low noise audio opamp for a mic preamp. The 741 opamp is 42 years old, is noisy(hiss) and has poor response above only 9kHz. I use TL071 single, TL072 dual and TL074 quad low noise and wide bandwidth opamps for audio circuits. Here is my mic preamp.
  19. audioguru2

    help bulding BJT amp

    Transistors have a wide range of current gain. Usually the voltage divider that provides base voltage has a current that is 10 times the base current of a typical transistor so it will work with a low gain or a high gain transistor. The current in your voltage dividers is very low and will not...
  20. audioguru2

    0-30V Stabilized Power Supply

    Hi Bugmenot, Here is a parts list that I made a few years ago using bigger resistors. It uses a BD139 for Q2. It uses high voltage opamps but you can use TL081 opamps from the original project and the voltage reduction circuit used by Ivan.
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