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  1. audioguru2

    help with solid state relay

    Your triac needs 50ma on its gate, not only 15ma. Why not more, maybe 70mA?
  2. audioguru2

    Redesign Elektor gigant2000 Amplifier

    The experts say that an amplifier with a peak output current of 5A (100W into 8 ohms) operates in class-B when one transistor conducts 180 degrees and the other transistor conducts the other 180 degrees. But most of the amplifiers made have both transistors conducting 50mA (class-AB) at idle...
  3. audioguru2

    Redesign Elektor gigant2000 Amplifier

    I disagree. 99% of amplifiers are certainly not class-B, they are class-AB. Many of these class-AB amplifiers have extremely low distortion. If they have a very small amount of gm-doubling distortion then it is buried way down in the noise level.
  4. audioguru2

    Redesign Elektor gigant2000 Amplifier

    Hi AN920, I mentioned the LM324 opamp because it and its sister the dual opamp LM358 are the first low-power opamps and they use insufficient bias current in their output transistors to reduce power consumption. They are the only opamps that have horrible crossover distortion. Class-AB power...
  5. audioguru2

    Sound Level Indicator

    Yes, but also R15 must be connected to +5V or many of the LEDs will light, because then pin 6 of the LM3915 will not have 0.47V but instead it will be 0V. Please measure the DC voltage on pin 5 and on pin 6 of the LM3915 when there is no sound and report the measurements here.
  6. audioguru2

    Redesign Elektor gigant2000 Amplifier

    Hi AN920, I have seen very simple class-B amplifiers (like the LM324 opamp) that do not have their bias "ridgidly controlled" (most do not have any bias) and they produce terrible crossover distortion. All the class-AB amplifiers that I have seen have a fairly small idle current of about 50mA...
  7. audioguru2

    mini audio amp 12VDC between Zumo 450 GPS and ear phones.

    Hi Mike,Welcome to our forum. ;D There are many small speaker amplifier ICs that will boost the output of earbuds. But the maximum allowable power will be exceeded so the earbuds will break. Hopefully before you become deaf.
  8. audioguru2

    need help power supply

    Hi Ante, If you  short one output of a power supply that uses a common transformer and the overloaded transformer begins to smoke then one output affects the other.
  9. audioguru2

    Help with medium range transmitter??

    Hi Limlim, Welcome to our forum. ;D It is a very low power, very poor quality FM transmitter: 1) Its antenna is connected to its tuned circuit so that if anything gets near the antenna then its frequency will change. 2) It doesn't have a voltage regulator so that the frequency will change as the...
  10. audioguru2

    Sound Level Indicator

    The "+" is +9V. The 10 ohm resistor in series with the LEDs, C6, the input of the LM2931, pin 3 of the LM3915, pin 8 of the dual opamp and the collectors of the transistors all connect to +9V. Then you have shorted the 10 ohm resistor. Connect the 10 ohm resistor in series with the LEDs as shown...
  11. audioguru2

    Sound Level Indicator

    Hi Jon, Pin 3 of the LM3915 is its positive power supply input. It won't work if it is disconnected. Measure the DC voltage at pin 5 and at pin 6 of the LM3915 and see if they are what I said in my last post. Also measure the regulated 5V supply to see if the regulator works properly. When you...
  12. audioguru2

    Sound Level Indicator

    Did you substitute any parts? The opamps? Without a signal, pin 5 of the LM3915 should be very close to 0V. The violtage rises as the sound picked up is louder. Without a signal, pin 6 of the LM3915 should be about 0.47V. Then the 10th LED should light when the voltage on pin 5 is 0.47V or more...
  13. audioguru2

    help transconductance amplifier

    The opamp has an extremely high input resistance because its input transistors are FETs. It has an open-loop voltage gain of typically 200,000 so the resistors set the closed-loop gain with their negative feedback.
  14. audioguru2

    Two PCBs off of one power source

    Hi Bruce, The LM4876 has the same pins numbers as the MC34119 and uses the same external resistors and capacitors. It has more output power but its max supply voltage is only 5.5V. It needs a resistor from its pin 1 Enable pin to the positive supply to turn it on and grounding pin 1 turns it off...
  15. audioguru2

    help transconductance amplifier

    Thank-you, Upsurt. Your new schematic is very clear as a GIF file type. But it was huge so I reduced its size, cropped it and made some of its dotted lines solid lines. I don't think the resistor in series with the load is needed. The voltage gain of the amplifier will be 1 when the load...
  16. audioguru2

    Two PCBs off of one power source

    Hi Bruce, I am soorry that I didn't know that the MC34119 low voltage bridged power amplifier is not made anymore. I still have a few. There are not many normal-size low voltage bridged power amplifier ICs still available because new ones are all tiny surface-mount types that are very difficult...
  17. audioguru2

    Redesign Elektor gigant2000 Amplifier

    Hi AN920, I agree that an amplifier should be designed for low distortion before a modest amount of negative feedback is applied. The OPA134 opamp has a very low distortion of 0.00008% at 1kHz with a gain of 1, and 10 times more with a gain of 10. Its open-loop gain at 1kHz is 10,000 times so...
  18. audioguru2

    help transconductance amplifier

    The schematic is small and is a very fuzzy JPG file type. It would be much clearer if it was made as a GIF or PNG file type. I can hardly see the part numbers. I cannot see the inverting and non-inverting symbols on the opamp. Why did you post the schematic "over there"? Please attach a clear...
  19. audioguru2

    Sound Level Indicator

    Hi Jon, I am sorry that the picture of my Veroboard layout is hard to see. I have brightened it and hope it is clearer.
  20. audioguru2

    Redesign Elektor gigant2000 Amplifier

    Hi AN920, We are talking about only 0.001% crossover distortion at 1kHz when the bias is optimal. It is masked by many other distortions and by noise. I know that crossover distortion increases at low levels but then the noise is also a higher percentage so there is more masking of the...
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