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fikic

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Posts posted by fikic

  1. Guitar Aplifier

    in Projects Q/A

    Posted

    I am saying, that I don't know, how to connect everything with the chassis. I also don't know, how to shield inputs. Can you tell me that? Beside that, I have power supply circuit on the same PCB than preamplifier and power amplifier

  5. Guitar Aplifier

    in Projects Q/A

    Posted

    I forgot to say, that it's only oscillating, when I power on circuit and have volume potentiometer set to minimum resistance..If I turn it to something bigger than 0Ohms it's cool to turn it back to 0Ohm when I power the circuit on. I am now reading current drawing from fuse of 25mA (I turned R9 to half of full resistance)....But sound is not ok..it is waving. What voltages should I messure and must be the same as in the LTSpice? I am posting some pictures from my messuring procedure. Second picture is speaker I am using now for testing. It's 4Ohms 15W speaker from old TV:

    post-45520-14279143987177_thumb.jpg

    post-45520-14279143988757_thumb.jpg

  6. Guitar Aplifier

    in Projects Q/A

    Posted

    I made new differend and better PCB, but circuit is still oscilating...only change, I made from original schematic was n-fet transistors Q1 and Q2. I used BF244A
    It is kind of a inposible to make new PCB and connect transistors wrong again to make circuit oscillate...I checked them again and I can't find error. What else can cause oscillating?

  9. Guitar Aplifier

    in Projects Q/A

    Posted

    I checked them all. They are all correct soldered. Only option left, I think is poor solder joint somewhere in the PCB. I am now making new PCB with differend software to make more mechanical compact pads. I will report.

  11. Guitar Aplifier

    in Projects Q/A

    Posted

    I tryed circuit without speaker. Instead of a speaker, I connected 12V, 21W lamp. It was unable to read current drawing, becouse one moment was 13mA and in the other was 30mA..it was changing every half second or faster. Lamp was little flashing. What could explain that?

  14. Guitar Aplifier

    in Projects Q/A

    Posted

    What if DC supply voltage is too high? The secundary of my transformer is 24V, but when I messure voltage in fuse socket (without fuse connected), I read 31V. This is 7V higher. Is this becouse of the filter capacitor, or is supply voltage too high?

  15. Guitar Aplifier

    in Projects Q/A

    Posted

    Did you manage to stop it oscillating?

    I swiched circuit on and loudspeaker screamed, then I quick turned it of and on again and it shuted up so I could make messurements. Should I still account your advice, to replace Q4? I don't understand your explanation for VBE of Q5 and Q6. Why is that voltage so low? Can you explain in newbe language please?

  16. Guitar Aplifier

    in Projects Q/A

    Posted

    Ok, I messured voltages somehow...:

    VBE of Q4 (voltage accross R10) was 0.6V
    VBE of Q3 was 0.6V
    VBE of Q5 was 0.3V
    VBE of Q6 was 0.2V

    Author said, that I must check also voltage across Collector of Q5 and negative ground and across Emitter of Q5 and negative ground. Both voltages should be half of voltage supply. However, voltage across Collector and negative ground was 34V, and across Emitter and negative ground was 15V. Can that explain my problem? What should I do?

  19. Guitar Aplifier

    in Projects Q/A

    Posted

    I really don't know what to do anymore. I checked everything and it's like in the original schematic. Why it doesn't work like it should? Resistors are right, especially R10 and R11 (I checked them hundreds of time). It is useable to change value of R14? Maybe it will work?

  21. Guitar Aplifier

    in Projects Q/A

    Posted

    That could explain differend current, through fuse, but not 10x higher, am I right? So I won't change nothing, even if I put r10 with 10k resistance in...I should check something else..but what? I checked every connection..If one of the transistors would be dead, amplifier wouldn't work at all would it? So, What do you suggest? What if I connected loud speaker wrong? In original, this speaker had a tweeter connected on (I think it was parallel). Could that be the problem? Should I connect tweeter with woofer?
    Oh, and you forgot to answer..

    I must also check trimmer, becouse I did something, that isn't in original schematic....:
    Did I do right thing to connect it like this? I thoud that in original schematic is mistake...

  22. Guitar Aplifier

    in Projects Q/A

    Posted

    Author said, that I must change value of R10 to bigger one in small steps. When I get right one, it will be ok. I will add potentiometer to R10 and when I messure right current, I will get potentiometer out and messure it's resistance, and then I will know, how much resistance I must give to R10 to be right one. Then I will replace everything with fixed resistor with value of R10+resistance of poteniometer.

    I must also check trimmer, becouse I did something, that isn't in original schematic....:

    schematic.png

    Did I do right thing to connect it like this? I thoud that in original schematic is mistake...

  23. Guitar Aplifier

    in Projects Q/A

    Posted

    I am sorry for my bad English. Yes, led is continuously lit. Resistor is connected like this: +---resistor---speaker----  -

    ...What if I change resistor R14 with bigger value and remove my resistor? Will then be better quality?

  25. Guitar Aplifier

    in Projects Q/A

    Posted

    Ok I replaced transistors and I tried circuit. When I REPLACE leads of avo-meter in fuse holder it mesures of about 100mA current. Speaker gives verry loud sound and when I remove leads of avo-meter, LED still flashes for few seconds. What can I check? It is this good behavier?

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