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  1. KrisBlueNZ

    Do I understand OpAmps wrong?

    What are the values of the resistors? Do the +2.5V and -2.5V supply voltages change as you vary the input voltage to the circuit?
  2. KrisBlueNZ

    Harman/Kardon HK6500. Loudness not working when button is pressed

    I think there's something wrong with your measurements. The amplifier won't work at all if there's no voltage on the outputs of D1. Here is the relevant part of the schematic. Near the right I have labelled the +V ("A" marking) and -V ("B" marking) supply rails that supply the power...
  3. KrisBlueNZ

    4-20mA using XTR111

    I see what you mean. You've shown one way to calculate RF based on RA and RB (that's what I'll call them) to give the right output voltage (0.4V) at the corresponding input voltage (0.5V) for bottom of scale. But how do you calculate the ratio between RA and RB? We know it's 1:1 because I...
  4. KrisBlueNZ

    Two inputs simultaneously

    Or you can save one resistor by using the transistor as an emitter follower and connecting the collector to one output and the base to the other, with the LED and current limiting resistor between the emitter and 0V. (Need to reduce the resistor to compensate for the base-emitter voltage drop)...
  5. KrisBlueNZ

    The 'bucket challenge'

    Some people "monetise" their YouTube channels - i.e. they collect revenue from advertising placed at the start of their videos. They don't get much unless they get LOTS of views - 10,000 at least. But they could donate that money to the ALS foundation. Personally I would rather support research...
  6. KrisBlueNZ

    Problem with Vintage Pioneer receiver SX-1000TW Output

    Right, good. Yes, fair comment. There is no regulator in the power supply, so there's no such thing as "regulated" values. Based on the fact that the voltage is shown as +82V on the amplifier schematic, and you measured +86V at one time, you could say that the 86V measurement was the "unloaded"...
  7. KrisBlueNZ

    Find Fault in my built amplifier

    OK, that construction looks reasonable. Can you post the voltages on all pins of all transistors? This should give us a clue what's wrong.
  8. KrisBlueNZ

    Harman/Kardon HK6500. Loudness not working when button is pressed

    I think you must be measuring those voltages wrong. If there was no voltage (or almost no voltage) on any of D1's pins, the whole amplifier would be dead. Try to find a good connection point for the 0V. If you have an RCA phono plug, unscrew the backshell and plug it into a socket on the back...
  9. KrisBlueNZ

    how to find resistor value ?

    Which supermarket? Ohm Depot?
  10. KrisBlueNZ

    Problem with Vintage Pioneer receiver SX-1000TW Output

    I'm happy to help where I can. You're obviously intelligent and you have figured out a lot by yourself without any hand-holding. This is a pleasant change from a certain category of users who ask vague questions and expect a perfect solution to be provided. Then you don't agree with me. Isn't...
  11. KrisBlueNZ

    STM32F105Rb CAN communication in loopback mode

    I have removed the ALL CAPS from your thread title. You want us to tell you whether there is a mistake in your program? Were you hoping we could read your program using a crystal ball, or "remote viewing"? Or do you think it might be a good idea to post your program here?
  12. KrisBlueNZ

    Harman/Kardon HK6500. Loudness not working when button is pressed

    Just measure the voltages on all of the pins. One pin on each capacitor is 0V and you should measure less than 0.01V. One pin on each capacitor is the supply rail and you should measure +40~50V on one of them and -40~50V on the other. Have you resoldered those connections? They look fine.
  13. KrisBlueNZ

    4-20mA using XTR111

    No problem :-)
  14. KrisBlueNZ

    Find Fault in my built amplifier

    Well, it's a bad idea to connect a small speaker to an amplifier that's powered from ±45V - one little click or pop, and your speaker is toast. Upload a photo of your construction, and mark up a copy of the schematic (preferably my readable version in the thread I linked to earlier) with the...
  15. KrisBlueNZ

    4-20mA using XTR111

    You wanted to convert a voltage range of (2.0V - 0.5V) = 1.5V into a voltage range of (2.0V - 0.4V) = 1.6V. Converting a 1.5V voltage variation to a 1.6V voltage variation requires gain, so you can't do it with just voltage dividers. Op-amps are the usual way to provide accurately controlled...
  16. KrisBlueNZ

    Problem with Vintage Pioneer receiver SX-1000TW Output

    In no circumstances would I replace only one of the output transistors - even if the unit was brand new. The other one is likely to have been stressed by the high current flow. And there's no point replacing the output transistors until you've fixed the problem that caused them to fail...
  17. KrisBlueNZ

    Wall adapter voltage issue

    OK. It's very unlikely there will be any problem. If the board uses the 12V rail for something other than generating the logic rail (using a regulator), that other function could be affected by the voltage being too high. But I don't think it would. The other concern is the regulator that...
  18. KrisBlueNZ

    Wall adapter voltage issue

    By "technical information" I meant a schematic diagram.
  19. KrisBlueNZ

    Find Fault in my built amplifier

    No, it's not just you! I wonder why they drew it like that. It makes me wonder if they've copied it from somewhere else, and redrew it all messed up to disguise this fact. But it's such a poor design that I doubt it's appeared anywhere else. And "never attribute to malice what can be adequately...
  20. KrisBlueNZ

    Find Fault in my built amplifier

    That schematic is extremely badly drawn. FYI I redrew it when it came up in an earlier thread: https://www.electronicspoint.com/threads/help-with-amp.262454/#post-1565548 To answer your specific question, that error would have forced the output hard to the negative rail. This would not have...
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