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  1. audioguru2

    0-30V Stabilized Power Supply

    To add Q1 back in I calculated the voltage divider values like this:
  2. audioguru2

    0-30V Stabilized Power Supply

    The original circuit used R13 and R14 to keep Q1 turned off when the positive unregulated supply was about +28V and the negative supply was -5.6V. When the mains power was turned off then the negative supply disappeared first allowing R13 to turn on Q1. To add Q1 to the latest circuit then the...
  3. audioguru2

    0-30V Stabilized Power Supply

    On the Tektronics circuit it looks like transistor Q15 shorts the output of the voltage error amplifier opamp U45 to ground when the main power is turned off. I did not see their discussion of it. I do not know which opamp they use since they do not use standard part numbers. The original...
  4. audioguru2

    IC doesn't fit in pcb

    The dual rows of pins need a pcb designed for it. Maybe you can make a little pcb for the IC pins then use wires to connect to the pcb you purchased.
  5. audioguru2

    IC doesn't fit in pcb

    Not enough details. Is the IC too big or is it too small to fit on the pcb? What is the IC? Is it an audio amplifier with two rows of terminals?
  6. audioguru2

    0-30V Stabilized Power Supply

    Thanks, Liquibyte. I hope you or Peter K will select and add one of the excellent pcb designs and place it in the sticky.
  7. audioguru2

    0-30V Stabilized Power Supply

    There are a few threads about this project. The latest BOM and schematic are many years old and have been posted hundreds of times in the threads. A few pcb designs have been shown. Recently a member organized these files and requested that a Moderator post them at the beginning of one of the...
  8. audioguru2

    0-30V Stabilized Power Supply

    Yes, most 10-turns trimpots have excellent quality. Yes, a wirewound resistor increases in value as it heats. Maybe yours is too small so it gets too hot? Maybe it is enclosed and gets hotter and hotter? Maybe it has poor quality?
  9. audioguru2

    0-30V Stabilized Power Supply

    The output transistors and the BD139 driver transistor get warm when they dissipate power. Power=  x voltagecurrent. So they heat when the current is high and the output voltage is low (because then these transistors have a high voltage across them). If you set the voltage to 30V, set the...
  10. audioguru2

    Simple question about a schematic.

    Hi Abador, I think we met on the other website forum. The datasheet tells you all about it. 1) In the low-cost circuit the Standby and Mute pins are connected together and are fed through a voltage divider with a slow delay capacitor C4. Vs is the supply voltage Vcc. 2) In the microprocessor...
  11. audioguru2

    Help with Audio Guru's Stethoscope.

    The wiring or the opamps are defective. Maybe you built the circuit on a solderless breadboard and its strips of contacts and connecting wires are picking up mains hum or causing high frequency oscillation. The maximum input offset voltage for a TL072 is listed on its datasheet as 10mV. The...
  12. audioguru2

    0v-30v power supply

    We have discussed the 0-30V power supply project for at least 9 years and I fixed its many problems a few times. The original defective project is still in the Projects Section of this site and there are a few very long threads about this project in the forum. Recently Peter K organized all the...
  13. audioguru2

    Help with Audio Guru's Stethoscope.

    Your mic might be defective. The datasheet does say it is an electret mic but I think it is. The polarity of its wires is not shown but I assume that red is signal and black is shield ground. Swap the wires to see if it works. If the unshielded mic wires are too long then they will pickup mains...
  14. audioguru2

    0v-30v power supply

    I used my experience. There is a similar power supply output circuit on this site. The opamp and output transistor fT's are not known so the values must be calculated properly to match them so that the amplifier has enough phase margin to prevent oscillation.
  15. audioguru2

    0v-30v power supply

    It has a few serious problems, Kevin: 1) Its voltage gain is only 1 because the negative feedback is wrong. 2) Its slow output transistor will cause oscillation without compensation capacitors. 3) Its maximum output voltage is about 26V instead of 30V. 4) It will be destroyed if the output...
  16. audioguru2

    0-30V Stabilized Power Supply

    The 28V transformer produces a peak voltage of 39.6V. If the maximum output current from your project is 2A then the transformer must produce 39.6V x 2A= 79.2VA. But the transformer is rated for 28V x 3A= 84VA so it will be very warm but be fine. 0.67 ohms is not a standard value, use 0.68 ohms...
  17. audioguru2

    Building an amplifier

    Since you do not understand the extremely simple schematic then maybe you should buy an amplifier that is already made. You were given 3 choices. Narrow down how much power, what supply voltage??
  18. audioguru2

    Building an amplifier

    In your other thread the TDA7297 bridged stereo amplifier IC was recommended. Did you see its datasheet? Newark has them in stock. A lowpass filter does not boost the bass, instead it cuts the highs. A bass boost circuit is half of a simple bass-treble tone controls circuit. Adding a subwoofer...
  19. audioguru2

    0-30V Stabilized Power Supply

    Hi Vakeiros, You can reduce the value of R7 to 0.33 ohms for a maximum output current of 4A but when the output voltage is low or is shorted then the driver and output transistors will get very hot. For a 5A circuit we recommend using 3 output transistors (each with a series emitter resistor)...
  20. audioguru2

    LM384N/NOPB-IC amplifier with heatsink

    I am amazed that there are still a few of these old car radio amplifier ICs still available in North America.
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