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  1. audioguru2

    transistors

    Hi Guys, An expert at The Amplifier Institute: http://dialspace.dial.pipex.com/prod/dialspace/town/pipexdsl/q/aqpl43/ampins/ampins.htm agrees with my discussion about the beta of transistors: BETA. Beta is not a fundamental property of a BJT. Never design circuits that depend on beta. Unless of...
  2. audioguru2

    RBG LED how to?

    Hi Madthug, I have seen RGB arrays being driven by analog current changes for its brightness changes. Are you planning to provide a unique PWM pulse width for each of the 3 colours for each pixel on the entire screen? ???
  3. audioguru2

    Hum in the incoming signal

    Hi Walid, Antenna coax cable has an electrostatic shield and so does audio cable with RCA or DIN connectors that connect stereo components together. All audio signals (not speaker outputs) must use shielded cable to avoid picking up interference. Audio cables that are installed in a building and...
  4. audioguru2

    transistors

    Hi Bjorn, If you bypass the emitter resistor with a capacitor having a very low reactance at the working frequency, then the transistor will have high gain and distortion. You can adjust the gain by using two emitter resistors in series, with only one of them bypassed. The two resistors could be...
  5. audioguru2

    BASIC FEEDBACK THEORY QUESTION

    Kevin, I didn't see your sketch before. It is a differential pair of transistors, definitely not an opamp. Its output resistance is high and its input resistance is fairly low, the exact opposite of an opamp. Therefore the negative feedback voltage divider is messed-up and is difficult to...
  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi NY, Welcome to our forum. ;D In this post we have talked about the 2N2219 getting too hot. You want to replace it with a tiny 2N2222A? It will melt. :( Your transistors are all different unsuitable types. Why not just purchase a cheap TIP31A that is recommended?
  7. audioguru2

    Hum in the incoming signal

    Your audio cable carries a low level signal and hopefully is electrostatically shielded. The mains cable carries a high voltage and current and its magnetic field goes right through the electrostatic shield of the audio cable. They must be separated. You could filter out all the bass of the...
  8. audioguru2

    Speakers

    Yeah. My decent speakers are sealed and have a flat response down to their resonance at 60Hz, then their response below falls at 12dB/octave. They have no problem playing with the full power of my amplifier so I made two underdamped Sallen and Key highpass filters with a 12dB/octave increase in...
  9. audioguru2

    BASIC FEEDBACK THEORY QUESTION

    Kevin, The ridiculous article about using a 10K output resistor to the negative supply was to operate its output NPN emitter-follower in class-A, to avoid the 0.00008% crossover distortion from its complimentary output PNP emitter-follower. You must remember that an opamp with negative feedback...
  10. audioguru2

    transistors

    Hi Bjorn, Transistors have a built-in Re. It is calculated by dividing the transistor's hIE by its hFE. Both change when the transistor's current is changed. Then the transistor's voltage gain is roughly the collector resistor (and the parallel load) divided by your calculated Re. Determining...
  11. audioguru2

    BASIC FEEDBACK THEORY QUESTION

    Opamps can't supply much output current for lower value resistors. The input impedance of opamps is so high the lower value resistors are not necessary. Most opamps have a minimum of 2k ohms load spec'd. In order for the load to receive most of the output then the feedback resistors must be much...
  12. audioguru2

    Limitation of current !!

    Hi Mukhalled, I am glad that your audio system doesn't have distortion anymore with the bass and treble controls in their normal centered position. ;D You can turn them up a little until you hear distortion again. In your car with the engine running and charging the battery, the voltage is...
  13. audioguru2

    transistors

    You can't change a transistor's built-in Re, but you can bypass its emitter resistor with a capacitor for high gain. Without collector to base negative feedback, a transistor without an emitter resistor is not stable with transistor changes from one to another, nor with temperature changes. A...
  14. audioguru2

    Limitation of current !!

    Hi Mukhalled, You shouldn't have the bass and treble controls at max. Speakers should sound normal with the bass and treble controls centered. There must be something wrong with the speakers or their enclosures for you to need to boost the bass and treble so much. When the bass and treble...
  15. audioguru2

    Infrared Activated Switch

    Hi Hamoodyjamal, You need a transistor to drive the low resistance relay because the obsolete LM307 can't supply enough current to drive it. Most opamps have a minimum load spec of 2k. Your relay is only 245 ohms! The LM307 current-limits its output current at 25mA. 25mA through 245 ohms is only...
  16. audioguru2

    transistors

    It doesn't matter if a transistor has a high current rating and a low beta, or a low current rating and a high beta. Beta changes with temperature and amount of current. The beta of a 200mA 2N3904 drops to about 70% of its highest value at half of its current rating. The beta of a 15A 2N3055...
  17. audioguru2

    555 Based Flyback/Ignition Coil Driver

    Your circuit doesn't need R5. R6 limits the current of TR1 and the base current of TR2. TR2 needs a resistor to ground at its base to turn it off quickly. ;D
  18. audioguru2

    50.000V Powersuply

    It sounds like you want 50kV at 1 amp. That's 50kW you know. If you want it to draw only 1A from 220V AC then it won't be monstrous. A little neon sign transformer has about 12kV. Add a voltage quadrupler and you have it. ;D
  19. audioguru2

    A timer question

    Hi Xoy, Set the 555 as an oscillator to have a full cycle in 6 seconds. At the end of each cycle, it latches the counter's reading and resets the counter. Then add a zero display digit to this display's right side and the whole display shows pulses per minute, updated each 6 seconds. ;D
  20. audioguru2

    Electronic Stethoscope

    Hi Xoy, That old counter circuit will work if you add another very low frequency lowpass filter so that it receives only heartbeats, I think I discussed it before. You also must use a Schmitt trigger device to produce pulses with rise and fall times much quicker than a 741 opamp can provide. You...
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