Help needed: Firing up the Aleph-X100

[Blitz]

...ok, checked insulation..everything OK. HAving done this, I checked each mosfet for vibrations and....no one of them did anything, so it was finally the @!?%&# current inrush limiter I had before the transformer. Now with 12 V both sides work as they should...Have not the time tonight to finalze it (especially to get 0 DC at the output), but for the moment I am happy, thanks a lot folks !

[Netlist]

Originally posted by Blitz
..so it was finally the @!?%&# current inrush limiter I had before the transformer.

Happy you found it.
However, it sounds strange to me that the limiter would only 'limit’ half a channel. Normally, when PSU's are faulty, both halves of the amp are affected. I still think half of that channel was not fully turned on. Please give us some more info about this 'special case'.

/Hugo

[Blitz]

Well...that as well is strang, but I guess you hint on applying 12V min here is really making the difference...which I didn't do becouse the limiter was so loud that I was afraid breaking something and turned off quickly.

[Blitz]

OK, I guess I work my way through...a hard way though.

After not longer having the problem above, I raised voltage further, until it started to smell and you heard things cracking.

Well...I am replacing all output-mosfest now(as some are broken and draw a lot of current)...found out that on one of the insulation was not OK and so the heatsink was under voltage...plus one soldering point which was broken...

OK, now with 12 V on the rail I have 0,12V over the 0,33R at the source on side A, but only half of that on side B.

Over the 392Rs I have as well a diffenrence: one has 3,53 V, the other 3,82 V, even though the 9610 have been matched closely. Maybe they have been damaged too ? the 100K trimmers don't help here really, the difference they make is marginal.

What would be your best shot ? Replace the 9610 or the BC550 first ?

Best Regards

[Netlist]

Something tells me that the 9610 has more chance to be damaged than the BC550. Change them, you'll see immediately what happens.
If all parts work, I mean nothing is damaged it's still possible to have both sides behave different because of trimming pots and slight mismatches of resistors.
However the amp should produce music in a primitive way, and the DC and bias should be adjustable within reasonable limits.

/Hugo

[Blitz]

OK, will do so. The resistors are all 0,1%, so I guess the pot adds more problems than solving it. But you are sure that the current drawn by each 9610 influences significantly the current drawn by the output-mosfets ?

[Netlist]

Originally posted by Blitz
But you are sure that the current drawn by each 9610 influences significantly the current drawn by the output-mosfets ?

Yes, this is very important and also has a big influence on the differential DC which is the DC seen by the load and measured between +out and -out.

/Hugo

[Blitz]

OK, I did in the meantime the following: Exchanged the BC550C (That was easy to do as I exchanged them before already and the leads where easy accessible) - no changes.

Cut the 9610 and soldered the left one to the right side and vice versa. Very interesting: Yes, the outout mosfets now draw on side B more currrent than the left side. But as well the ratio now (without connecting each 9610 onto the same heatsink) changed: before the change the left side drew three time higher current than the right side, now it is only 50% more on the right side than on the left side...

OK, taken this as encouranging signal, I started to increase voltage to approx. 18V on the rails which lead to something around 0,43V across the 0,33 source resistors (5Watt wirewounds). Shortly after that two resistors started to smoke and where gone. This happened last time as well when raising power over a certain level, so the problem can be reproduced (last time it killed as well the mosfets.) (Still without having a restor connect between the output as I think the whole think should not implode when no speaker is present).

So what happens here now ? My theories ( and I would be happy to understand your thoughts):

A- When increasing power, the resistors change their value (become smaller), which again raises current to a level which finally kills the reistor as well as the mosfet.

B- 5 Watt resistors are simply not robust enough to handle 1,5A and 0,5 Volt (should have been OK, right?)

C. The mosfet (044n) hates more than 1,2 A current and breaks and kills subsequently the reistor - I planned to use only 8 devices per channel with 100 Watt as this drives 1,5 A through each device @ 22V

D. The two mosfets destroyed are those, which have no direct connection to the BC550C, the other two survived - a co-incidence or clearly part of the problem ?

[Netlist]

A) Not true, the resistor value increases or decreases only with a very small percentage when warming up. You could look it up in the datasheets if you find one. Look for ppm.

B) 0.43V/0.33ohm is 1.3A. 0.43V * 1.3A = 0.56W. 5Watt resistors for sure can handle this.

C) According to the datasheet the irfp044N can take 53A at 10V 25°C and 37A at 10V 100°C. You are far from there.

D) No idea.

You should definitely change the 9610's.
Measure each mosfet as stated in Remco's post.
Check for mistakes in your wiring. Take your time for that.
Try to launch the amp with output mosfets gates detached and measure and tweak till the voltages on both sides are normal.
That's about what I can think of for the moment, if something more comes to mind I’ll tell you.

/Hugo

[Blitz]

OK, found another faulty insulator ( but not under the two dead mosfets) which again has set the heatsinks under voltage.

The resistors died because the mosfets died before- So even with very little voltage I have now a couple Amperes over them, which extend the 5 Watt by a lot.

I will now exchange these nasty silpad 2000 insulators which simply cause only trouble against regular stuff.