Aleph 2 project burning problem


i am building an Aleph 2, and have a problem:

At the moment i power up the amp:

R11 and R12 are burning up in flames.
Q3 breaks, Z5 also.

The rest of the board seems to be ok.

I tested this two times, thought i had a defect Q3 while assembling the board. But it was the same effect.

The schematics (and the part numbers) are the same as in the original Pass documentation. I checked everything about 5 times and can´t see the mistake i made.
My rail voltages are a bit higher than in the originals, i have +-49V instead of the +-45V. Can this 4V more cause the Problem? (I don´t think so)

Now i am absolutely out of ideas what the problem could be and ask you for your help.

I attached my schematics and board layout.

Regards, Martin


  • Mainboard_SCH.PDF
    11.6 KB · Views: 78
  • Mainboard_PCB.PDF
    57 KB · Views: 75
  • IRFP240- PCB.PDF
    13.3 KB · Views: 59
Some parts have pin changes over time - especially if they come from different manufacturers. I was bitten by this on my first amp build. If this is not the case, check your board carefully for inadvertent solder bridges. If you are using an old Aleph-2 board that came from this forum, the solder pads for the small signal transistors are VERY close to one another. Use a fine-tipped flat-blade screwdriver to physically scratch between solder pads when you finish your solder work.

edit - just saw your pcb, so it's not the old one from here, but the advice is still good. Make sure there are no solder bridges. Use a bright light and check carefully.
Thank you for your quick answers.

Check orientation of Z5. And value of R13. Also, high res pics is a must have.
orientation and value is ok. Pic is attached, hope the quality is good enough.

also take care of not mixing drain , gate source and sense
...this is what i think i have done :)

Check value of R13
Check that R13 is not shorted out
Check Zener operation before installing new one
Check for shorts on mosfet pads
Zener was checked in the 2nd try, i THINK there were no shorts.

So you think it is not my PCBs or the 49V, but a wrong/defect part or a soldering problem?

Making short circuit somewhere while soldering seems to be unlikely, because the two boards showed exactly the same effect ???

I´ll check again for shorts on the boards.

Regards, Martin


  • 20200204_095806.jpg
    896 KB · Views: 122