Search results

  1. audioguru2

    0-30V Stabilized Power Supply

    If you use LM324 opamps with a max supply of 32V then a power supply project must be re-designed for the lower raw supply voltage of about 30VDC (which rises to about 32VDC when there is no load) and the max output will be about 24VDC at 3A. Look at www.farnell.com and look for the flag of your...
  2. audioguru2

    0-30V Stabilized Power Supply

    I selected the TLE2141 or MC34071 opamps because their max supply voltage rating is 44V and they are available almost anywhere in North America. The LM324 has a max supply voltage rating of only 32V which is much too low and it is a quad opamp (it has 4 opamps) not a single opamp.
  3. audioguru2

    0-30V Stabilized Power Supply

    Hi J Rhodes, Since U1 output is almost correct (it should be 11.2V) then with the voltage pot set to max the input to the U2 and transistors amplifier is 11.0V or 11.2V. The feedback resistors R12 (56k) and R11 (27k) in series with the voltage calibration trimpot set the gain of the U2 and...
  4. audioguru2

    Step Up Battery Voltage Problem

    Every cheap multimeter can measure DC current. Buy one. It can also measure the battery that might have its voltage drop when the stepup IC has a load.
  5. audioguru2

    Step Up Battery Voltage Problem

    You forgot to tell us how much is your output current. You also did not tell us how low the battery voltage drops with your load.
  6. audioguru2

    Noise Canceling Headphone

    On the internet there are a few projects for noise cancelling headphones. They glue electret mics to the outside of each earphone and have an amplifier and mixer circuit to electronically cancel outside noise. You need a hearing specialist (or common sense) to determine which frequencies are...
  7. audioguru2

    0-30V Stabilized Power Supply

    The dissipation in the 0.47 ohm resistor is I squared R. so with a current of 3A it dissipates 3 x 3 x 0.47= 4.23W which makes a 10W resistor very warm. 4A creates a dissipation of 7.52W which is a lot of heat in the small space of a 10W resistor. One trimpot adjusts the input offset voltage of...
  8. audioguru2

    Impedance matching for E.guitar and cellphone/ipad/itouch

    Impedances in audio are never matcheded. A low source impedance feeds an amplifier input resistance that is much higher. The output resistance of a solid-state amplifier that feeds an 8 ohm speaker is not 8 ohms, it is 0.04 ohms or less. Your cell phone has a electret microphone that has a very...
  9. audioguru2

    0-30V Stabilized Power Supply

    The reference voltage from U1 is 11.2V. You want the max output to be 30.0V. Then the output amplifier (U2 plus the driver and output transistors) must have a gain of 30.0/11.2= 2.679 times. The gain is not affected by the voltage drop of the transistors because they are inside the negative...
  10. audioguru2

    0-30V Stabilized Power Supply

    It sounds like you are looking at the original version (and it is a kit) that has many problems. The latest version has been posted here in these threads many times. It uses a 6A to 10A rectifier bridge module that can be bolted with heat sink compound to a metal chassis or a heatsink. The...
  11. audioguru2

    What do you mean by 3 1/2, 3 3/4 digits specs for a DMM

    The first digit on some digital multimeters is simply a 1 or a 0. It is called "half a digit" so if it reads 1.555 then it has three and a half digits. Some digital multimeters can show 7.555 then maybe they have three and 3/4 digits.
  12. audioguru2

    0-30V Stabilized Power Supply

    The peak voltage of a 25.5V sine-wave is 36.0V. If there is no load then the full-wave rectifier has a drop of slightly more than 1V so makes a filtered 35.0VDC.
  13. audioguru2

    0-30V Stabilized Power Supply

    Your 24V 400VA transformer has poor voltage regulation for such a powerful one. Also its voltage is too low so the max regulated output from this project at 3A will be only about 25V instead of 30.0V. A much smaller Hammond 28V at 5A (140VA) transformer increases to only 29.5V without a load.
  14. audioguru2

    0-30V Stabilized Power Supply

    Yes, yes and yes.
  15. audioguru2

    Active Bass & Tremble Controller

    I think an "A" pot is logarithmic and can be used for a volume control. A "B" pot is linear and is used for tone controls. Simply turn the pot to halfway rotation and measure the Ohms from one end to the middle slider terminal. A linear pot will measure half the total resistance of the pot and...
  16. audioguru2

    0-30 Vdc Stabilized Power Supply

    Then you built the original version instead of the fixed and improved version that uses a BD139 driver transistor. It has current regulation, not short-circuit protection. If you build the latest version that has calibration trimpots then when the current is set to 3.0A and the output is shorted...
  17. audioguru2

    1 Simple question about led drivers

    No. LEDs are driven with current, not voltage. The voltage should be higher than required then the current-limiting resistor or circuit absorbs the extra voltage. No. Voltage regulators are never paralleled. The datasheet for the LM317 shows how to add a single inexpensive power transistor to...
  18. audioguru2

    0-30V Stabilized Power Supply

    The maximum total allowed supply for the MC34071 and TLE2141 is 44VDC. A 30V/5A transformer is probably 31.5V without a load then its peak is 44.5V and is rectified to make a supply of 43V. So it is close. If your mains voltage is higher than the specs of the transformer then the supply voltage...
  19. audioguru2

    0-30V Stabilized Power Supply

    The -1.3V supply is regulated by the two series diodes. The voltage will never go as high as -1.5V as you show.
  20. audioguru2

    0-30V Stabilized Power Supply

    The -1.3V supply has a very low load current so its ripple is very low. Its voltage is regulated by the two series diodes. The latest version will not work with the rare and very expensive OPA445 opamps that we used about 6 years ago. It uses common and inexpensive MC34071 or TLE2141 opamps...
Top