KP, please measure voltage across R16 as Ben suggested.
2.1V across R17 means a lot of current is flowing through Q6. At that level, R17 will burn out quite quickly.
I'm guessing if you measure the voltages across R18 and R19 they will be somewhat higher than 0.4V as well.
You mentioned measuring across the outer pins of the the mosfets
and got ~0.5V for Q5 and Q6. The two outer pins should give you a Vgs
measurement which is inconsistent with current flowing through Q6.
I agree with Anand's suggestion of testing those mosfets.
2.1V across R17 means a lot of current is flowing through Q6. At that level, R17 will burn out quite quickly.
I'm guessing if you measure the voltages across R18 and R19 they will be somewhat higher than 0.4V as well.
You mentioned measuring across the outer pins of the the mosfets
and got ~0.5V for Q5 and Q6. The two outer pins should give you a Vgs
measurement which is inconsistent with current flowing through Q6.
I agree with Anand's suggestion of testing those mosfets.
Voltage on R16 is .2mv. That is low compared to the others.
I want to get new mossfetts on the way in case one is bad.
Would these work?
8x Matched IRFP240 N-Ch POWER MOSFET 20A 200V 150W . VISHAY / SILICONIX | eBay
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If they're matched, you can use the IRFP140s in the Q5/Q6 positions.
Q6 is the likely problem. It might be bad part, or you might have a short there.
The ~1V across R18/R19 is the current limiter (Q3/R13/R14) in action with
about 2.25A going through Q7 and Q8. The ~4.5A gives you the 2.1V across R17.
Also the ~5.6V across R7 is roughly what is needed for Q7/Q8 to conduct that current.
Q6 is the likely problem. It might be bad part, or you might have a short there.
The ~1V across R18/R19 is the current limiter (Q3/R13/R14) in action with
about 2.25A going through Q7 and Q8. The ~4.5A gives you the 2.1V across R17.
Also the ~5.6V across R7 is roughly what is needed for Q7/Q8 to conduct that current.
You can do a quick Vgs measurement:
https://firstwatt.com/pdf/art_matching.pdf
A couple hundred mA current should do.
That said, I suggest first checking for shorts and the status of your existing parts.
https://firstwatt.com/pdf/art_matching.pdf
A couple hundred mA current should do.
That said, I suggest first checking for shorts and the status of your existing parts.
Dennis you are the MAN!
I will go back and test those mossfets so I can learn about that. But for now I am going to celebrate! It is working by swapping out Q5 and Q6 for the pair of irfp140 mossfets.
Bias and DC offset are adjustable now!
I cannot explain how happy I am and how grateful I am for your help and Anan and everyone else who helped me.
Zenmod called out my soldering joints and he was right. I probably overheated those fragile jfets and mossfets.
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I have followed this with interest. I applaud your tenacity Kingsportal! You had it rough and you were almost ready to throw in the towel a few days ago. Glad you stayed on it and a huge kudos to this community that was able to overcome your own frustration and keep on being patient and willing to help further when it looked like it was a lost battle.
Really interesting! Enjoy your amp!
Really interesting! Enjoy your amp!
That is too cool. You watched me a complete novice suffer through this project. I wish I could say it was fun. Lol.
I do enjoy building stuff so in terms of that it was fun. The troubleshooting was for the real experts here in this community that took time and effort to reach out to help a stranger. For that I a grateful to all!
I do enjoy building stuff so in terms of that it was fun. The troubleshooting was for the real experts here in this community that took time and effort to reach out to help a stranger. For that I a grateful to all!
