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  1. Audioguru

    Battery Powered Variable Power Supply

    The requirements have conflicts: 1) A portable variable power supply that has a regulated voltage and current. Like those nifty bench power supplies. 2) I'm looking for efficiency above all. A linear power supply has excellent voltage and current regulation but has poor efficiency. An efficient...
  2. Audioguru

    Breadboards are awesome!

    I don't pick parts at random and "try them" to see if they work in a circuit. Instead I learned the basics of electronics and use circuit theory for a design and parts datasheets to see the spec's of parts to be used in a circuit. Then almost no parts need to be changed for my circuits to work...
  3. Audioguru

    Battery Powered Variable Power Supply

    A current regulator usually reduces the output voltage of the power supply until the current is at the current setting. If the output is shorted then the current regulator must force the output voltage to zero but it has a diode in series with its output so the output of the current regulator...
  4. Audioguru

    Battery Powered Variable Power Supply

    13 years ago I helped fix the project you linked because it had many overloaded parts, was not reliable and did not produce its rated 30VDC at 3A. The improved project has some very long threads about it at electronics-lab. Recently there are a few very cheap Chinese copies that also do not...
  5. Audioguru

    Breadboards are awesome!

    Many posts on these forums ask, "Why does a circuit not work?". I ask, "Is it built on a solderless breadboard?". A solderless breadboard has: 1) Intermittent contacts that are not soldered. 2) A tangled mess of wires all over the place that makes troubleshooting very difficult. 3) Capacitive...
  6. Audioguru

    volts, signal and circuits

    A tone control does not cause a strange backflow that reduces the volume capabilities or makes the tone completely unfunctional.... Instead it simply gradually boosts or cuts high or low frequencies. A tone control should be used only when the input signal source, amplifier or output speaker...
  7. Audioguru

    to make a ultrasound speaker

    A proper specification of frequency response says how much the output level deviates from being flat. +/- 3dB is audible but the cheap piezo tweeter specifies 4kHz to 27kHz without saying how much deviation. Maybe it has a huge notch of -30dB at 22kHz? Maybe 27kHz is at -60dB?
  8. Audioguru

    24v battery to 12vdc for stereo possible?

    A 12V car stereo advertised for 200W puts out 14 Watts per channel into four 4 ohm speakers at reasonably low distortion. At 200 Whats it is clipping like crazy and producing tonnes of distortion. Then why do you need 100W speakers? Because the 100 Whats rating is also a lie, it is for a very...
  9. Audioguru

    to make a ultrasound speaker

    Many piezo tweeters "claim" to produce frequencies to 27kHz but they lie about it. They fall off above 18kHz. Here is a typical piezo tweeter: Look at "Does an ultrasonic repeller repel mosquitos?" in Google and many answers are NO. Mosquito zappers were sold with a propane flame making CO2...
  10. Audioguru

    Power-One power supply mod

    In Google, I entered a search for Farnell and found them in many countries including South Africa. They are a good electronic parts distributor, try them.
  11. Audioguru

    Power-One power supply mod

    You will need to adjust the calibration (a value change of a resistor) so that the maximum is 25V or it will produce an maximum output a little more than 25VDC that is full of ripple and without any voltage regulation.
  12. Audioguru

    Power-One power supply mod

    It seems that RS do not know what they are selling. The photo shows 2 x 15V but the description is for a 2 x 12V transformer. If it is only 2 x 12V then the power supply will not produce much more than 25VDC at 3A. If the transformer is 2 x 15V then it will be a little overloaded when the power...
  13. Audioguru

    Transistor gate voltage

    A 100W rheostat was used 100 years ago. Where will you find one today? Today we use a pulse-Width-modulation circuit controlled by a small inexpensive potentiometer or computer.
  14. Audioguru

    Rechargeable Power Supply Question

    I have posted a video of a fake Cheap Chinese 18650 cell so many times that I won't post it this time. I lost the image of a fake protection circuit glued to the end of a cheap ordinary 18650 cell. The fake protection circuit is a photo that looks like a real circuit. That is how the cheap...
  15. Audioguru

    Rechargeable Power Supply Question

    You can read about all the things a lithium battery charger circuit must do to prevent the dangerous lithium battery from exploding or catching on fire when it is charging. Datasheets for the Charger ICs also explain all the important steps like sensing a low voltage before charging then...
  16. Audioguru

    Conundrum using resistors? (Raw rookie)

    Hobby King sells cheap Chinese junk that does not last long. Their cheap Lo-Po batteries for RC airplanes are so bad that it seems that they are sold without being tested.
  17. Audioguru

    Rechargeable Power Supply Question

    The first one doesn't say much and leaves you guessing. The second one with battery protection has many more features and details.
  18. Audioguru

    Rechargeable Power Supply Question

    The cheap Chinese charging board (the ad said 2 cells but a thumbprint photo showed a jumper to make it for one cell) has no spec's and might not work with a 5V input. An 18650 cell with low voltage cutoff must be used so that the cell is not ruined by its voltage dropping below about 3.2V.
  19. Audioguru

    Rechargeable Power Supply Question

    No. A "cell phone charger" is simply a 5V power supply to feed the charging circuit in the phone. The 3.2V to 4.2V lithium battery cell will overcharge and blow up and/or catch on fire without a charger circuit.
  20. Audioguru

    Conundrum using resistors? (Raw rookie)

    But the power supply is 5V and each LED is 3V. So with 2V across the 1k ohms resistor then the current is very low at only 2mA. He says only one 100 ohm resistor and 4 LEDs. He doesn't say or show if the LEDs are in series or in parallel. Of course if the LEDs are in series then no current will...
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