I replaced Q3, Q4 and Q5 which the transistors used in the other channel and zeners started regulating better (maybe the previous transistors were not very well matched?).
I connected the amp and measured at the beginning about 3 volts at output and it was going slowly down, when it was about 2,3V it jumped to something about 10V or 11V DC
I measured all the resistors again. VR4 is 0 Volt again, but this time but when I remove the BC559 (Q11) I can measure hFE with the tester... I suppose this means it's working, anyway I replaced it.
The values I measured this time are:
VR1=0,0228V
VR2=0,0228V
VR3=0,1 mV
VR?=0,433V
VR4=0,00V
VR5=2,698V
VR6=0,03V
VR7=14,55
VR9=23,8
VR10=0,05mV
VR11=0,01mV
VR13=0,319V
VR14=0,321V
VR15=2,28
VR16=oscillated from 0,13mV to 0,60mV
VR17=39,4V
D1 and D2=3,95V
D3= 8,98V
I hope I can find the problem out...
I connected the amp and measured at the beginning about 3 volts at output and it was going slowly down, when it was about 2,3V it jumped to something about 10V or 11V DC
I measured all the resistors again. VR4 is 0 Volt again, but this time but when I remove the BC559 (Q11) I can measure hFE with the tester... I suppose this means it's working, anyway I replaced it.
The values I measured this time are:
VR1=0,0228V
VR2=0,0228V
VR3=0,1 mV
VR?=0,433V
VR4=0,00V
VR5=2,698V
VR6=0,03V
VR7=14,55
VR9=23,8
VR10=0,05mV
VR11=0,01mV
VR13=0,319V
VR14=0,321V
VR15=2,28
VR16=oscillated from 0,13mV to 0,60mV
VR17=39,4V
D1 and D2=3,95V
D3= 8,98V
I hope I can find the problem out...
Hi,
what is this telling us?
Could it be an overheated component dying after a brief period of oscillation?
I didn't use matched transistors when I built the amp,... do you think that this could cause the oscillation?
If this were the case, can I match them measuring them in the tester with the "hFE" function? or should I build a matching-tester?
If this were the case, can I match them measuring them in the tester with the "hFE" function? or should I build a matching-tester?
VR4 is zero because of the positive output voltage. Problem appears to be the opposite of the original - no current seems to be flowing through Q9. R6 should always have about 3.4 volts across it - the voltages you measured show almost no voltage at all. unmatched input transistors will cause small amounts of offset, but you shouldn't worry about this until you get the major problems straightened out. I would be looking for Q9 open or bad connection of base or emitter of Q9. Good luck.
VR6 was about 3,54V ; I think I typed wrong when posting...
I realized that the BC639s I bought last time were different than the firsts I was using (I went to a different provider) . I bought about 8 and just used them for the amp...but today I realized that when measuring hFE the value I got was something like 2,5... and 140 for the other ones (the "good" ones).. I could rescue just one from the "bad" ones...😡
I checked the board and saw that Q6 was a "bad" BC639, so I replaced it and got the problem solved!
The DC offset couldn't be adjusted at all, it was about 18mV... a little less than the recommended value (20mV), so I left it as it was.
Then I polarized the power transistors to 50mA and connected the amp to the PC for testing with music. At the beginning there was no sound and the speaker's cone moved back and standed there, the tester indicated about 5-6V DC, but this only happened if the amp had a load connected. So I connected the amp directly to the power supply (without the safe ressistors) and the amp turned on in 1 to 2 seconds (during that time there was some plops and cone displacement).
I could hear music but sounded noisy and without bass response, when I disconnected the power supply from the mains, the amp sounded much better for the seconds that the caps ramained charged...(I suppose this is not a power supply's issue because I use it with my actual amp)
I checked again the DC offset and was about 100mV so I corrected it... (and I thought that it could be a reason for my amp sounding bad)
When adjusting the quiescent current again I made a mistake... a wrong connection of the tester made me believe the voltage across the 0,22 ohm was 0,3mV (when I wanted from 11 to 15 mV) so I continued moving the pot, but then I smelt that something got hot and the LED of the power supply turned off... OUGH! I quickly moved the pot back and disconnected everything...(the fuses I use are mounted on my other amp's board... so this test was unfused! big mistake of mine)
I still can adjust DC offset and quiescent current, but when connecting the amp I just hear a plop and then nothing... surely I blowed some drivers or the power transistors...
I almost had it!
I couldn't replace the drivers yet because I have no more time for today but I'll post the news soon🙂 (please no more problems with this amp!)
Thank you for reading and helping me!
I realized that the BC639s I bought last time were different than the firsts I was using (I went to a different provider) . I bought about 8 and just used them for the amp...but today I realized that when measuring hFE the value I got was something like 2,5... and 140 for the other ones (the "good" ones).. I could rescue just one from the "bad" ones...😡
I checked the board and saw that Q6 was a "bad" BC639, so I replaced it and got the problem solved!
The DC offset couldn't be adjusted at all, it was about 18mV... a little less than the recommended value (20mV), so I left it as it was.
Then I polarized the power transistors to 50mA and connected the amp to the PC for testing with music. At the beginning there was no sound and the speaker's cone moved back and standed there, the tester indicated about 5-6V DC, but this only happened if the amp had a load connected. So I connected the amp directly to the power supply (without the safe ressistors) and the amp turned on in 1 to 2 seconds (during that time there was some plops and cone displacement).
I could hear music but sounded noisy and without bass response, when I disconnected the power supply from the mains, the amp sounded much better for the seconds that the caps ramained charged...(I suppose this is not a power supply's issue because I use it with my actual amp)
I checked again the DC offset and was about 100mV so I corrected it... (and I thought that it could be a reason for my amp sounding bad)
When adjusting the quiescent current again I made a mistake... a wrong connection of the tester made me believe the voltage across the 0,22 ohm was 0,3mV (when I wanted from 11 to 15 mV) so I continued moving the pot, but then I smelt that something got hot and the LED of the power supply turned off... OUGH! I quickly moved the pot back and disconnected everything...(the fuses I use are mounted on my other amp's board... so this test was unfused! big mistake of mine)
I still can adjust DC offset and quiescent current, but when connecting the amp I just hear a plop and then nothing... surely I blowed some drivers or the power transistors...
I almost had it!
I couldn't replace the drivers yet because I have no more time for today but I'll post the news soon🙂 (please no more problems with this amp!)
Thank you for reading and helping me!
Hi again
I checked al transistors and replaced just one of them.
I still have the same problem that commented in the previous post: the amp sounds noisy when I connect it, and seems that it sounds fine when power is removed, during the 1 or 2 seconds that the caps remain charged.
The power supply's caps are 4700uF, and it works fine for my other amp... do you think anyway that it could be a power supply problem? I cannot test whit another power supply as I have just this one for the moment...
I checked al transistors and replaced just one of them.
I still have the same problem that commented in the previous post: the amp sounds noisy when I connect it, and seems that it sounds fine when power is removed, during the 1 or 2 seconds that the caps remain charged.
The power supply's caps are 4700uF, and it works fine for my other amp... do you think anyway that it could be a power supply problem? I cannot test whit another power supply as I have just this one for the moment...
I have seen that I connected the input inverted, so signal was going directly to GND, it would have never worked that way 😀
Now I'm listening to it, a better bass response is noticeable, the woofer cone has more movement than with the other amp (using the same power supply), maybe that major difference is explained by the MJ15024 and MJ15025 power transistors (my other amp uses IRF540 Mosfets transistors).
I think quiescent current could be a little higher if it's intended for a full ranged amp, but as I will use it with an active croosover (310Hz freq cut) it's quiet fine as is (about 50mA)
I want to thank again to all of you who helped me!
I'll be sharing some photos in the "Post your Solid State pics here" thread soon.
Now I'm going for the other channel and the Caps bank for my new 400VA transformer !
Cheers
Now I'm listening to it, a better bass response is noticeable, the woofer cone has more movement than with the other amp (using the same power supply), maybe that major difference is explained by the MJ15024 and MJ15025 power transistors (my other amp uses IRF540 Mosfets transistors).
I think quiescent current could be a little higher if it's intended for a full ranged amp, but as I will use it with an active croosover (310Hz freq cut) it's quiet fine as is (about 50mA)
I want to thank again to all of you who helped me!
I'll be sharing some photos in the "Post your Solid State pics here" thread soon.
Now I'm going for the other channel and the Caps bank for my new 400VA transformer !
Cheers
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