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  1. audioguru2

    Wireless intercom

    Hi Wood, Welcome to our forum. ;D You have a few things to think about to make a wireless intercom for 4 units: 1) How to dial one of them and have it receive but also have the others blocked. Do you transmit a different radio frequency for each one? Or do you 1st transmit a tone that "opens"...
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    Yup. You would light-up too, like U2 and U3 if your supply voltage is way above your absolute max. It looks like you need some OPA445AP high voltage opamps. I can't remember what you are using for Q2. If is the original little thing and it fails, it might wipe-out your new opamp. Get a real...
  3. audioguru2

    Electronic Memory!

    Hi Mukhalled, I don't know how much current a CD-drive uses nor its minimum operating voltage but I think it needs a huge very expensive capacitor to power it while starting your engine. What powers your amp while starting? Connect them to the same connection. ;D
  4. audioguru2

    Audioguru FM Tx

    Hi Walid, 1) Resistors are only 5% but a Vbe of 0.8V is a whopping 33% higher than 0.6V. 2) The graph for Vbe ON Voltage is different from the graph for Vbe Saturation Voltage and you should use the correct one (ON Voltage). 3) The graphs in my Fairchild datasheet don't have figure numbers. It...
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Helder, 2) Your measurement is high because the value for pots could range over plus and minus 20% which is fine. 3) Your measurement is low because you probably used a zener diode designed to be operated at 45mA, but R4 in the circuit gives it only 1mA. That's why I recommend using a...
  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Helder, It's troubleshooting time! 1) Turn the current regulation setting pot P2 to max and connect the neg lead of your voltmeter to the output 0V terminal. 2) Without a load on the project measure the voltage at the slider of P2. It should be about +1.7V. If it isn't, check the vaues of...
  7. audioguru2

    BJT biasing formulas

    I know what you mean but it might be confusing for others. I would say "Since the gain is 10 then choose RC=10RE values that give you the desired IC." ;D
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    The short-circuit current is determined by the setting of the current-regulation pot, P2. In your original project's circuit with the pot at max I think Q2 and Q4 will melt with about 2.5A. The voltage across R7 is the load's current times 0.47.
  9. audioguru2

    Audioguru FM Tx

    Hi Walid, You should never assume Vbe in a transistor circuit that has a low emitter voltage. It is typically 0.62V on my datasheet. I used the parts I had. I didn't have 320k for R2 nor 60k for R3 so the divider current to base current ratio is 20:1 instead of 10:1 which better controls the...
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Helder, A current meter is made by using a low-value resistor in series with the load, and measuring the voltage created across it. R7 in the circuit is already in series with the circuit, so the voltage drop across it is caused by load current through it, but its voltage drop doesn't reduce...
  11. audioguru2

    BJT biasing formulas

    You can't buy nor find resistors with the "odd (unusual) values you calculated. You need a voltage gain of 20 so choose resistors with common values like 2k and 100 ohms. I don't make nor want the VE to be low. The voltage gain requirement of 20 dictates that the voltage across RE is 1/20th of...
  12. audioguru2

    Can I find transformer regulation?

    The resistance of its primary will cause a fixed voltage drop when loaded and the resistance of the secondaries would also cause a voltage drop . A formula for removing turns could be worked out if you knew the number of turns.
  13. audioguru2

    Can I find transformer regulation?

    If you counted its secondary turns you would have a formula to calculate how many turns to remove, but the secondary is probably wound in layers and can't be counted accurately. So just remove turns until the loaded voltage is correct. If you are using both windings in parallel, make the number...
  14. audioguru2

    amp problem

    Does the hiss sound go away when you disconnect the input to the amp? Was the amp good before and the hiss sound is a new problem? Did you add new speakers with better or peaky tweeters? Is the amp trying to whisper something to you? ;D
  15. audioguru2

    Power Line Commucation Help Find Info

    I don't think the mains power signal cares about only 1V or less of high frequency broadband signal. If millions of users had BPL then the voltage would drop a little, due to losses in the filters.
  16. audioguru2

    Power Line Commucation Help Find Info

    What is BPL? ???
  17. audioguru2

    BJT biasing formulas

    Hi Wald, Your calculations are correct but you have the same problems as before: 1) The dictated collector current requires odd resistor values. Select the RC and RE resistors first. A standard 2k for RC and 100 ohms for RE will result in a gain of 20 and a collector current near 2mA. 2) The...
  18. audioguru2

    Simple battery charger

    Hi Yevgeni, Of course a battery charger must be designed for the chemistry of the rechargable battery because a lead-acid, Ni-Cad, Ni-MH or Lithium batteries are all different. Most rechargable batteries need current-limited charging because they have such a low internal resistance. They would...
  19. audioguru2

    infrared burgar alarm with rf transmitter and receiver

    Hi Joi, Welcome to our forum. ;D You didn't attach its schematic so what should we do? Guess?
  20. audioguru2

    amp problem

    Hi Omer, What is a "tis" goming sound? Is it high frequency noise that sounds like and we call "hiss"? If it goes away when you disconnect an input then the noise comes from the source that feeds that input. If the hiss noise comes from the amp then is the amp a manufactured one or an amp you...
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