Hi!
I have built an Aleph 3, but whein I fire it up I get: SMOKE!
I am only using one output-mosfet (and one in the current source) per channel, and I have resized accordingly.
What happens it that both R118 and R109 (aleph 3 scematic)smokes (even glows in the dark), and I turn it off ...
I am troubleshooting it now, but can't seem to locate the problem.
I am using a bc550c instead of the mpsa18, and I have checked them.
The rails are +/- 26VDC unloaded.
Some help would be greatly appreciated
I have built an Aleph 3, but whein I fire it up I get: SMOKE!
I am only using one output-mosfet (and one in the current source) per channel, and I have resized accordingly.
What happens it that both R118 and R109 (aleph 3 scematic)smokes (even glows in the dark), and I turn it off ...
I am troubleshooting it now, but can't seem to locate the problem.
I am using a bc550c instead of the mpsa18, and I have checked them.
The rails are +/- 26VDC unloaded.
Some help would be greatly appreciated
Hi Kristijan!
R109 burns first, then R118.
I wasn't able to check any voltages, because it happened so fast.
PS -it is the same on both channels. My theory now is that maybe I have wired something incorrectly. Refering to your Aleph 5 board I am only using the outhermost MOSFETS and the resitors for them (the one on the left, and the one on the right side of the board). As far as I can see this should work fine, as the banks of 3 MOSFETS are in paralell, but maybe I have missed something. I'm at work , so I can't check it right now.
Since I am not paralelling MOSFETS, I haven't tested the MOSFETS (IRFP250). Maybe they are faulty
R109 burns first, then R118.
I wasn't able to check any voltages, because it happened so fast.
PS -it is the same on both channels. My theory now is that maybe I have wired something incorrectly. Refering to your Aleph 5 board I am only using the outhermost MOSFETS and the resitors for them (the one on the left, and the one on the right side of the board). As far as I can see this should work fine, as the banks of 3 MOSFETS are in paralell, but maybe I have missed something. I'm at work , so I can't check it right now.
Since I am not paralelling MOSFETS, I haven't tested the MOSFETS (IRFP250). Maybe they are faulty
to make a long story short: IT WORKS!!!
Kristijan, you where right, Q108 was damaged (along with Q106 and R122).
The reson for this is that Q104 & Q105 was incorrectly oriented at the first try.
All voltages check out fine, except across Q105 = 3,2 V
And the voltages across R120 and R122 is only 0,3V.
So it is severly underbiased, and I can hear some ugly distortion when I try to push it a little (increase the volume). At goes away at low volume. At least I hope it is distortion due to the very low bias (R120/R122 measure too much with my multimeter also 0,3/0,4 ohms).
I will try another type of source resistors( paralelled 0,47 ohms 5W ww), and also leave R113 out of the circuit to try to increase the bias. Worst case I get 2,8A bias on a single MOSFET: BWAAHAAA!!
Thanks for your input guys!
Kristijan, you where right, Q108 was damaged (along with Q106 and R122).
The reson for this is that Q104 & Q105 was incorrectly oriented at the first try.
All voltages check out fine, except across Q105 = 3,2 V
And the voltages across R120 and R122 is only 0,3V.
So it is severly underbiased, and I can hear some ugly distortion when I try to push it a little (increase the volume). At goes away at low volume. At least I hope it is distortion due to the very low bias (R120/R122 measure too much with my multimeter also 0,3/0,4 ohms).
I will try another type of source resistors( paralelled 0,47 ohms 5W ww), and also leave R113 out of the circuit to try to increase the bias. Worst case I get 2,8A bias on a single MOSFET: BWAAHAAA!!
Thanks for your input guys!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.