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  1. audioguru2

    audioguru fm transmitter

    Both Q2 and Q3 are tuned RF stages. It will be fine.
  2. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    6A with hardly any ripple is pretty darn good! ;D
  3. audioguru2

    Digitally selected outputs for LM317

    Darlington transistors don't saturate so have a pretty high voltage drop when turned on. A transistor array IC would be better because a transistor can saturate with a very low output voltage. Then the current in the voltage-adjustment resistors is predictable.
  4. audioguru2

    Digitally selected outputs for LM317

    Hi Zeppelin, the resistors need something to drive one with 10mA, so a Cmos output won.t be strong enough. Think about driving the transistors with a binary group of signals, the 4 transistors would give 16 voltages, 5 transistors would give 32 and 6 transistors would give 64 voltages etc.
  5. audioguru2

    Op Amps gain

    No. The voltage gain of most opamps is 100dB. 60dB is a voltage gain of 1,000 and every 20dB more multiplies the gain by 10 so 100dB is a voltage gain of 100,000. Some very high gain opamps have a voltage gain of 120dB which is 1,000,000. An opamp has an extremely low input power and a low...
  6. audioguru2

    Ante 50 Years Young

    We have lots of fun fooling around like we are young again. ;D
  7. audioguru2

    Ante 50 Years Young

    I'm 60 and feel like I am still 30 or 40 years old (young). ;D
  8. audioguru2

    Disadvantages of simple filters

    A chebychev filter has ripple in its passband and has extrene phase fluctuations. A Butterworth filter has an absolutely flat frequency response then a sharp cutoff. Its phase response is reasonable. A Bessel filter has a droopy frequency response and the least amount of phase shift.
  9. audioguru2

    Very long RC time contant!

    You could cook up a few circuits from the applications that are shown on datasheets.
  10. audioguru2

    about mixer

    Your audio mixer adds signals together without making new frequencies. A radio's mixer multiplies the input RF signal and the local oscillator which makes new sum and difference signal frequencies.
  11. audioguru2

    Help me to explain the LM3915 operation.

    Correct. ;D
  12. audioguru2

    audioguru fm transmitter

    There are hundreds of FM transmitter projects on the internet. I just copied the best features of a few of them, then added a low dropout voltage regulator and some pre-emphasis. I calculated North America's 75us of pre-emphasis by using 75u/470 ohms= 160n so I used 150nF. I calculated Europe...
  13. audioguru2

    Very long RC time contant!

    That is not true. A capacitor has phase-shift that causes the response to be 0.707 instead of half the voltage. Half the voltage is created by two equal resistors that don't have phase-shift. Look at RC filters in Google.
  14. audioguru2

    Disadvantages of simple filters

    Each stage of an LC passive filter provides a drop of 40dB per decade. An RL or RC passive filter is only 20dB per decade. I use active filters with a sharp-cutoff Butterworth response for most audio filters. I have used switched-capacitor lowpass and bandpass filter ICs to make extremely low...
  15. audioguru2

    audioguru fm transmitter

    It won't make much difference, but your tuning caps are with a low value so make the 10-turn coils so that the frequency adjustment goes low enough. The coil in the pic has a 3mm former and so does the coil in the sketch. I used the "Z" case that is in a TO-92 small transistor case. You can use...
  16. audioguru2

    Very long RC time contant!

    Of course a sinewave or any other waveshape is affected by the time constant of a coupling capacitor. At the frequency where the reactance of the capacitor equals the impedance of its load, the circuit's output level is down 3dB which is a loss of -0.707.
  17. audioguru2

    Very long RC time contant!

    You are probably talking about an audio coupling capacitor. The time constant of the capacitor with the impedance of the input of the next stage is usually calculated to form a highpass filter, so at the cutoff frequency the signal begins to be impeded and is not cleanly passed.
  18. audioguru2

    audioguru fm transmitter

    Of course the supply voltage for a transistor circuit matters. The transistor will fail if its max voltage or power dissipation are exceeded. The supply voltage determines the power output. The power dissipated by the parts must be calculated and parts are selected that can handle the calculated...
  19. audioguru2

    10 A FET

    Digikey and Newarkinone have thousands of Mosfets at many voltage and current ratings. Most are rated with 10V gate drive. Their price doesn't agree with their ratings but is set by how many of a certain type are sold. I don't know what brands are available in your area so I can't make a...
  20. audioguru2

    audioguru fm transmitter

    Hi Windoze, My FM transmitter is rock solid stable in its RF frequency, has a range of more than 2km to my sensitive car radio and home stereo tuner, sounds very clear due to its low distortion and pre-emphasis (treble boost like radio stations have) and still works fine (although with reduced...
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