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  1. KrisBlueNZ

    stepping down 300v ac

    I guess your simplest option is to put a load resistor across the secondary of your 220VAC->12VAC transformer, and a resistor in series with the primary. I'll assume a maximum dissipation in the load resistor of about 2W, so you can use a 5W resistor. The load resistance can be calculated as...
  2. KrisBlueNZ

    Trying to fix home subwoofer amplifier. Any help is appreciated.

    I don't think an oscilloscope is needed - yet. But this is a Class D amplifier so it will be very useful later to check the PWM drive signals. This is significant because all the PWM stuff is done with op-amps, not with a dedicated control chip that could just be replaced on suspicion...
  3. KrisBlueNZ

    stepping down 300v ac

    He wants to monitor the voltage using a microcontroller. I assume the microcontroller's 0V rail will be earthed, and the transformer output will have to be floating, so he needs isolation.
  4. KrisBlueNZ

    Trying to fix home subwoofer amplifier. Any help is appreciated.

    What's happening with this project? It looks like sheldonstv has lost interest. Have you cleaned up the repairs? Can you upload a new photo? Do you still want to get this thing going?
  5. KrisBlueNZ

    why are these transistors getting so hot?!

    Have you got an oscilloscope? If so, see whether the amplifier is starting to oscillate at high volume settings. Actually that's unlikely, unless the output transistors are getting hot too. The positive and negative voltages that feed into those regulators... where do they come from? Is it just...
  6. KrisBlueNZ

    Driving an array or Piezo sounders

    If you want to deliver maximum power to your transducers, make the tuned circuit a series tuned circuit, with the inductor in series with the transducers. This gives the maximum voltage across the transducers. I imagine that multiple transducers would be best connected all in parallel. The...
  7. KrisBlueNZ

    Compression by the resistor

    Thanks for the feedback :-) To be picky though (which I am), the capacitor's resistance doesn't change as it charges up. The voltage across it increases, but it's not meaningful to say that its resistance changes, because resistance only relates to something with the quality of a spring, where...
  8. KrisBlueNZ

    Need an advice. Have idea to create simple computer , with punched card programming

    If you want to be able to spend most of your time designing, redesigning and optimising your architecture, and relatively little time wiring, rewiring and diagnosing wiring errors with huge numbers of components, you would be best to learn about programmable logic devices such as FPGAs, from...
  9. KrisBlueNZ

    panasonic sa-ht70 dvd player sound

    I wouldn't be too worried about putting a high AC or DC voltage into the Aux input. They're high impedance and no significant current will flow. But possibly the amplifier uses a bridge-tied load and has its outputs sitting above 0V (at half the power amplifier's supply rail voltage). If that's...
  10. KrisBlueNZ

    Compression by the resistor

    Wow! Your English is excellent! I thought the French resented having to speak English. Yes, it seems like a natural way to present the lesson. Start with the basic idea, then give it the full engineering treatment. Right. Personally I would throw them all out and buy new ones. They aren't that...
  11. KrisBlueNZ

    Compression by the resistor

    Hi Robyn... or is it Rob? I read further on the page you linked to, and the author goes into a lot of detail on improvements that can be made to the design. He mentions the zener breakdown of the PNP transistor, but doesn't mention that it does temporary and/or permanent damage to the...
  12. KrisBlueNZ

    Guitar Amp Modification

    A chromatic tuner is a device that listens to the pitch of the sound from an instrument, detects which note name the pitch is closest to, and allows you to tune the instrument to exactly the right pitch for that note. The scale used in Western music contains twelve different note names; the...
  13. KrisBlueNZ

    Help with "Data switch"

    Yes, 4800 bps is fine. You're welcome; no problem. Good luck!
  14. KrisBlueNZ

    Compression by the resistor

    See my post on your other thread on this subject. That oscillator has a design error and will damage the PNP. Use a power supply voltage of 6V. You may need to change resistor values to make it oscillate reliably with 6V power supply. davenn, would you merge the two threads please? They are...
  15. KrisBlueNZ

    Compression by the resistor

    Hi Robyn, That oscillator circuit generates a "curved sawtooth" oscillation at the output, but the point in the circuit where the output is taken from is a "high impedance" point in the circuit. You can think of it as being "weak" or "flimsy". "Loading" it, by connecting resistors with...
  16. KrisBlueNZ

    diy logic probe

    You mean why are the LEDs connected from the outputs to VCC? Exactly why you said. The comparator outputs are open-collector, so they only sink current; they cannot source current. In other words, they close to ground when low, but when they're high, they do not pull to VCC. The load needs to be...
  17. KrisBlueNZ

    Help with "Data switch"

    Try again; I've just updated that post with a complete diagram.
  18. KrisBlueNZ

    diy logic probe

    I'm not sure what your question is. If you mean the connections to the inputs of the comparators, that is just the way they need to be wired so that each comparator output goes low in the appropriate state and lights the corresponding LED.
  19. KrisBlueNZ

    Help with "Data switch"

    I'm not sure. There's a simpler way to do this, though. Here's a circuit that may be suitable. Here's a circuit description. The two GPS receivers connect to CN1 and CN2. The top terminal of each connector is for the RS-232 data from the GPS receiver to the PC. The PC connects to CN3. The...
  20. KrisBlueNZ

    stepping down 300v ac

    I think maybe he has a variable transformer, and he wants to monitor the output voltage. He mentioned a minimum voltage of 160 VAC and a maximum of 300 VAC.
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