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  1. Audioguru

    Bench power supply upgrade

    You can leave in the VD3 zener diode. The resistor feeding it needs to have the part number of the zener diode to match its current that might be 20mA or much more. If you use a 30VDC power supply plus a negative supply feeding a resistor in series with the VD3 5.1V negative zener diode then...
  2. Audioguru

    Bench power supply upgrade

    Sorry, I did not see your tiny numbers clearly. Yes R17 and R18 must remain. Remove VD3, VD4 and VD5, R16, R19, C6 and C7. Sorry again. C8 filters the opamps positive supply at high frequencies and must remain. R17 picks up the output current in R6. R17 and C4 are a filter for stability. Yes...
  3. Audioguru

    How change the Frequency of a 555 timer with another circuit ?

    The datasheet of the LM358 shows a VCO.
  4. Audioguru

    Bench power supply upgrade

    VD3 MUST be removed be replaced with -5.1VDC, not the +5.1V that you show. Remove VD3, VD4, VD5, C7, C8, R17 and R18. R4 still connects to the wrong place and R8 still has the wrong value and also connects to the wrong place. If you do not recalculate then change the value of R23 and R24 then...
  5. Audioguru

    Bench power supply upgrade

    I see that the Chinese copy corrected the error on the original schematic connecting R19 to the correct negative-going terminal of the bridge rectifier.
  6. Audioguru

    Bench power supply upgrade

    1) A 24V transformer will produce 25V or more when it is no fully loaded. Then the positive supply to the opamps will be +34V or more. With the -5.1V negative supply then the opamps will get a total of 39V or more which will blow up the opamps since their maximum allowed total voltage is only...
  7. Audioguru

    Can anyone create a Gerber file of the attached sloppy schematic?

    I notice that the power LED is connected backwards.
  8. Audioguru

    someone to settle a LED confusion that i have please

    The 21V is not "split". Instead it is fed as 21V to R212 and R213. The calculation of original red LED current in post #9 has a decimal point error. The current is (21 V - 7.2 V)/150 Ω = 9.2mA. Too much current burns out or shortens the life of LEDs. The current in your four series blue LEDs...
  9. Audioguru

    Bench power supply upgrade

    1) The input to the bridge rectifier is where a 21VAC transformer powers the circuit. Then the circuit gets +27VDC and -5.1VDC. 2) Fix the errors of R4 and R8. 3) Recalculate the value of R26 to match the current rating of zener VD6. 4) Recalculate the value of R24 so that there is voltage...
  10. Audioguru

    Transistor prototype photo

    It is funny that you weigh your money (gold bars?) in pounds and we measure our money in dollars. It is also funny that you drive on the wrong side of the road but we drive on the right side. Your lorry is our truck, etc.
  11. Audioguru

    someone to settle a LED confusion that i have please

    The existing red LEDs already have one resistor or a resistor in series with each LED. Remove the red LEDs and replace them with the blue LEDs (the anode and cathode must not be reversed) then either there is not enough voltage for the blue LEDs or they will be dim.
  12. Audioguru

    Bench power supply upgrade

    The original kit and the Chinese copy have some errors:
  13. Audioguru

    Bench power supply upgrade

    Two of the old TL081 opamps and a transistor in the Chinese power supply kit need a regulated -5.1V at about 26mA or more. Since their maximum allowed total supply voltage is only 36V then the positive supply for them must never exceed 36V - 5.1V= 30.9V. Then the maximum loaded output from this...
  14. Audioguru

    Sloppy Schematic Questions

    The diodes labelled D1 to D4 chop off the peaks of the triangle waveform creating a horrible looking "sinewave". The lousy old LM324 opamp produces crossover distortion and noise. It has a very poor high frequency response.
  15. Audioguru

    My first circuit is a bit advanced (H-bridge!)

    Why do you have switches when you said that PWM pulses are used? The calculations are simple. You did not show a schematic but I found one for you, I removed its diodes for clarity. Your breadboard layout does not show a power supply voltage or the PWM pulses voltage. Your new little...
  16. Audioguru

    My first circuit is a bit advanced (H-bridge!)

    You need a 3V to 6V battery that can produce 0.8A to 1.6A. The little 9V battery cannot produce a current of more than 400mA for a few minutes. The S8050 transistor also cannot produce the high current.
  17. Audioguru

    A Phoney Question

    The speaker appears to have five terminals with a red wire on the left terminal and a black wire on the right terminal. The text on the speaker cannot be seen. The wires are for the audio signal with the black wire probably a signal ground.
  18. Audioguru

    A Phoney Question

    Maybe the third speaker wire is to its metal frame as a signal ground?
  19. Audioguru

    A Phoney Question

    The earphone of a phone plays both sides of a conversation. Connect the earphone to the input of your mixer with a shielded audio cable. It will be a low line level or a high mic level. Some earphones also produce a wireless variable magnetic signal that can be picked up with a sensor fed to a...
  20. Audioguru

    A Phoney Question

    I do not know why you want to feed phone sounds to your mixer. If you connect the phone's earphone to an amplifier then you will have acoustical feedback squealing when the handset mic hears the amplified sounds. A speakerphone has an electronic switch that cuts off its speaker when you talk and...
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