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audioguru last won the day on March 11

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  1. Most of the spec's for the headphones are absolutely useless. The frequency response spec's do not say plus and minus 30dB which is horrible or plus and minus 2dB which is pretty good. Who cares about the length of the cord and the weight? The important spec for the ear speakers is the impedance that you can measure with a multimeter but you didn't. If the circuit is modern then it uses tiny little parts that are difficult to solder and unsolder.
  2. audioguru

    LED panel .

    Can you provide a link to the ebay ad? Your schematic shows strings of 3 LEDs in series and a tiny resistor is also in series. Your pink and blue lines show that all the strings are in parallel. Since a white LED is about 3.2V to 3.6V then the entire bunch of LEDs uses a 12V supply.
  3. You have 12V, not plus 12V and minus 12V which is 24V. What you label as -12V is actually 0V. An ordinary older type of Lithium Ion cell is 4.20V when fully charged so your charger should have an output up to 12.6V, not 12.0V. The charger circuit should have wires connected between the series batteries so that it makes it a balanced charger.
  4. The circuit is the same as the old Greek kit here except a few part numbers are changed and the maximum output current is only 2A. It also has the problem of an overloaded transformer since with a 2ADC output the 25VAC input is 2.83A, not 2A. I ,saw some 741A opamps rated at 44V which might work but I do not think the maximum output voltage will be 30V, probably only 26VDC at 2A with lots of ripple. I wonder which circuit came first?
  5. I have some Li-PO batteries for my RC airplanes that had hundreds of flight and had storage for a few winters. I can charge one and use it and it produces a problem like you have but it charges normally. The battery is worn out and cannot produce normal power continuously for a normal duration. Measure the output voltage of the L298 that feeds the motor. If it drops lower and lower then also measure the input voltage of the L298 to see if it drops when the motor is slowing down. A Lithium rechargeable battery quickly becomes ruined if its voltage becomes less than about 3V per cell. my airplanes pulse the motor power as a warning to me that the voltage is becoming low then the motor stops but allows the steering servos to control the glide.
  6. Maybe your battery is not fully charged. Measure its voltage while the motors are running.
  7. Yes, the pots short circuit the input signals when turned down because they are shown wired backwards, instead of wired like volume controls.
  8. Sorry, I do not have time to modify this power supply for you.
  9. Sine you need a maximum output of only 15V and since most ordinary opamps have a maximum supply voltage of 36V then use an 18V transformer and the -5.6V negative supply as in the original project. The BD139 driver transistor and two 2N3055 output transistors in the latest version of this project should be used and the value of the resistor in series with the voltage calibration trimmer must be increased to set the maximum output to +15V.
  10. I think this old circuit should be kissed goodbye and be buried.
  11. audioguru

    LED panel .

    I cannot see which connects to what. Can you provide a schematic?
  12. The original circuit should work fine up to 15V at 1A if you replace the old opamps with the newer higher voltage ones. You probably should recalculate the resistors that set the maximum voltage and current outputs. If the Chinese kit uses the transistor that shorts the opamp output when the power is turned off then the resistors that feed the transistor need to be recalculated for the reduced voltage. I have used perforated stripboard for many projects including very complicated ones. The copper strips are cut to length with a drill-bit and become almost half the wiring of a pcb. The parts and a few short jumper wires become the remainder of the wiring. Only one wire is in each hole so changing a part is easy like on a pcb.
  13. There are a few completely different types of phones and you do not say which one. Landline phone, wireless phone and cell phone. Take one apart and look inside then count the components. Why???
  14. If the battery is good then it should power the circuit for a few hours when it is fully charged.
  15. When the negative supply collapses to 0V when the positive supply is still 37.8V then the current in both resistors in series is 37.8V/(12k + 160 ohms)= 3.1mA. If the base is +0.65V then the current in the 160 ohms needs to be 0.65V/160 ohms= 4.1mA so the 160 ohms resistor value and the negative supply voltage are too low. I removed Q1 and somebody else later added it back in wrongly.
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