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  1. audioguru2

    Need help with 3916 super project

    That is normal. The opamp has an internal voltage gain of 100,000 or more. So only 10uV between the inputs will cause the output to change 1V or more. R8 provides negative feedback so when the input to R9 swings to -2V, then each transistor's output rises to +3.57V. You said before that the...
  2. audioguru2

    12 V DC to a 220V AC Inverter AMplfier Design

    You could make a modified sine-wave with a CD4047 oscillator and a CD4001 quad NOR gate or CD4011 quad NAND gate. The oscillator of the CD4047 and its Q output would be gated and drive one of the push-pull output transistors. The oscillator output and the Q-Not output would be gated and drive...
  3. audioguru2

    Need help saturating a transistor for 2 amps

    Hi Indulis, I disagree. A transistor is fully saturated when its collector-base junction becomes forward-biased. This can't occur in the bottom transistor of a darlington, so its "saturation" voltage is always higher than a base-emitter voltage drop.
  4. audioguru2

    10A 1.2 to 20V power supply

  5. audioguru2

    Need help with 3916 super project

    R7 connects the input pin 5 of the opamp to 0V. Without a signal, R8 provides 100% DC negative feedback so that the emitter of Q1 and pin 6 are also at 0V. The output pin 7 is at one base-emitter voltage drop above the voltage of Q1's emitter. A signal causes Q1, Q2 and Q3 to rectify it and...
  6. audioguru2

    10A 1.2 to 20V power supply

    How are you going to cool the MJ15004 power transistor when it must dissipate 313W?? It will melt. You will need many power transistors mounted on a huge heatsink and a high velocity fan. The 25VAC transformer produces a peak voltage of 35.4V. The rectifier bridge will make a voltage of...
  7. audioguru2

    Need help with 3916 super project

    I think your LM358 dual opamp works normally. When you touched the meter lead to pin 6, the mains hum picked-up by the lead was amplified by the opamp producing +0.9V. My LM3915 is 6 times more sensitive than your LM3916 and my project displays a few LEDs if a pin is dropped on the floor on the...
  8. audioguru2

    Need help with 3916 super project

    The input voltages of an opamp should be the same. Yours has pin 6 very different from pin 5. Replace it.
  9. audioguru2

    How can I make a guitar fuzz effect

    Not very well. The LM386 is a small power amplifier, not a preamp. Just make a preamp with a high input impedance from an opamp.
  10. audioguru2

    How can I make a guitar fuzz effect

    Sorry MP but you are wrong. R3 is the input resistance of the inverting opamp amplifier which is 1k ohms. The 0.47uF input coupling capacitor has a reactance of 1k ohms at 340 Hz, so the load to a guitar pickup is only 2k ohms at 340Hz and less at higher frequencies. Many experts say that a...
  11. audioguru2

    Audioguru FM Tx

    The only 2903 that I know is the LM2903 dual comparator IC. It is not a low-dropout voltage regulator. All semiconductor manufacturers make a 5V low-dropout regulator in a small plastic transistor case.
  12. audioguru2

    Audioguru FM Tx

    They are just audio coupling capacitors. A higher value will pass lower audio frequencies. 330nF passes frequencies down to about 40Hz, 470nF will pass audio frequencies down to 28Hz and 220nF will pass audio frequencies down to 60Hz, with the impedances of the circuit. Their values don't need...
  13. audioguru2

    Need help with 3916 super project

    Close enough to half of 5.0V. That is a problem. The mic preamp opamp has C2 in series with its negative feedback voltage divider. Therefore its DC voltage gain is 1 and its DC output voltage should be the same as its input: 2.44V. I bought mine a long time ago at Digikey. Sorry, I haven't seen...
  14. audioguru2

    Need help with 3916 super project

    The mic preamp circuit in my project should work fine with your half of an LM358 dual opamp, it just won't have high audio frequencies. Measure the DC voltage at pin 1, it should be 2.5V if you used a 5V regulator. The case of the electret mic is connected to its ground pin and the ouput pin...
  15. audioguru2

    Need help with 3916 super project

    Another problem with using a messy breadboard. It is good that you found it. Let us hope that nothing is damaged. That is close to 0V and maybe just caused by interference picked up by your long wires. The LM3916 has a 12k ohm ladder at pin 6 while my LM3915 has a 28k ohm ladder. Therefore...
  16. audioguru2

    Theory discussion moved from Q/A

    Transistor manufacturers make similar transistors have different pins, just to fool the noobies: A BC547 has pins in the sequence of CBE. A 2N3904 transistor has them as EBC. Some little transistors have the middle pin as the collector. If the pins are wired backwards then the base-emitter...
  17. audioguru2

    Need help with 3916 super project

    Your driver opamp circuit has an output level way too high! The signal at pin 5 of the LM3915 is DC since Q2 is a peak rectifier. Maybe your preamp is oscillating or picking up mains hum. My microphone's cable is only about 4cm long but is a shielded cable so it doesn't pickup interference. It...
  18. audioguru2

    How can I make a guitar fuzz effect

    It is the same circuit as the opamp circuit by Jesus a couple of days ago. Its 1k input imedance is too low for a guitar's pickup.
  19. audioguru2

    Electronic Stethoscope

    Our member, Con, made this excellent pcb design for the corrected and improved 2nd version of the Electronic Stethoscope-2 project:
  20. audioguru2

    Knight Rider with Halogen Bulb

    Darlington transistors also have a resistor between base and emitter.
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