need help for an aleph2

I'm an assidute reader of your wonderful forum.
After a while, I decided to build an aleph 2.
Knowing nothing in DIY, I've been amazed to find everything I needed by reading your posts ( sorry for my bad english).

But now, I've got a big big problem !

Everything go right until I put on the amp :
everytime I put the amp on, Q5 (ZTX450 : can't find MPSA18) burn out and the IRFP240 smokes.

When I don't connect the output bank, here are the values :
+/- 45,6 V
Q5 : 0,186 V between C and E
Q4 : 9,5 V between C and E

I think that I've checked everything, but there still is a mistake.

Help !!!!!!
 

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Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
The input diff pair is trying hard to drive the negative
output MOSFETs, and that's why you see the 9.5
volts across Q4.

First off, get a Variac and use it to slowly turn on the
AC line voltage, while watching the current draw with
an ampmeter.

You did not mention which IRFP240 smoked.

Is the output voltage positive when you "fire" it up?
 
help

I'm very impressed : NELSON PASS answering me !!!!!
I'm glad to try building Aleph 2 just for that : I think you're the most famous person I talked to !!! Thank's a lot for your help !

The IRFP burned out are the one attached to the top right of mark's layout (the tracks going between the led anod and cathod).

where can I measure the output voltage (I'm a true newbie and very bad at speaking english !!) ?
on the spots going to the speakers ?
 
help

without connecting the output boards, I have +44,6 V between speaker + and speaker - !

The Irfp not only smoked, they're out of order ! and two 221 R resistors are out of order too (one on each output board).

Any suggestions ????

Another thing : when I turn on the amp, the led lights on, but after a few seconds it lights off.

Help please !!!!!!!!!!!
 
Re: help

ndhennin said:
without connecting the output boards, I have +44,6 V between speaker + and speaker - !

The Irfp not only smoked, they're out of order ! and two 221 R resistors are out of order too (one on each output board).

Any suggestions ????

Another thing : when I turn on the amp, the led lights on, but after a few seconds it lights off.

Help please !!!!!!!!!!!

The only thing I can say, is let a friend, girlfriend, wife etc. check out everything! Somehow you are missing something. Try to find an electronic friend or teach a friend/wife/girlfriend a bit about most of the things and let him check everything without you watching his back... You either are making the same structural fault (like diodes backward etc.) or looking over it about ten times!

Check small things, +/- of capicitors, zeners cathode/anode, gate of mosfets etc. and let it be checked by friends!

Edwin
 
I remember having similar problems when trying out my first amp 20 years ago. It came out that one transistor was of the wrong polarity and the whole thing was smoking.

I can only suggest to remove all active devices (there are not too many of them), checking them out, you probably have a meter, then put everything together and check again for any mistakes. In your case that would be probably fastest way to sccess. Remember, if your circuit is not working it is either wrong component or bad connection, check carefully for both.
 
Aleph 2 : It works great !!!!!!
I solved the problem : I don't know exactly what it was : I changed the burnt fets, the ZTX450 and the 1 ohm resistors, take my amp to see a friend of mine who has a variac, oscilo.... and he told me everything was OK !!!!

Just finished the second channel yesterday evening at 00:00:00 and listened to music till 04:00:00. GREAT!!!!!!

Thank's to everyone in this forum for the help : it wouldn't have been possible without you since I'm a true newbie in electronic (my only project before this one was a pair of speakers).

I'm now waiting for the amps to burn in and will tell you my impressions later (when I'll be more objective).

I'll post some pics later (I'm leaving for holidays).

Thank's again, and I'm now waiting for the active crossover.......
 
ndhennin,

Great to hear that your amp is working now. Isn't this forum great?

Even though some of the gurus here are tired of our newbie (sometime silly) questions, I'll still post and ask questions anyway.

I find that if one were to write down on paper (or in this case, on the keyboard) what the problem was, it helps to organize your own thoughts and sometime you'll figure out a solution yourself if you sleep on it for a few nights! Also, someone on this forum will always be willing to help.