Aleph 2 uneven temperatures

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Hello, I just completed Aleph 2

1500v toroid 0-44vx2
6x 69000uf 50v capacitors + 1 ohm RC filter
dual isotop fast recovery bridge

I used k&k boards

I finished putting in the components and sound is good but is it normal source resistors are different temperatures? I used matched mosfets. Source resistors are 5% (i know- bad thing) 5w 1ohm. They all get warm but some are hotter than others.

Also, how does a burned mosfet influence output sound? (just to know)

Can some test be done on finished board to check mosfet health?

Thank you
 
And how about power supply voltages across you supply caps?
About 56-57 volts?
44V AC secondaries seems to little bit high for 50V caps.
But we are fearless burning amp builders. :)

You know in my Aleph a 100.000 uF 50v cap had burnt once ago.
My DC voltages is exactly 50 V. Although those elcos are rather old.
Actually, it does not burnt, but was escaped that foul electrolyte, through the safety vent.
It was huge smoke and a terrible smell.

Gyuri
And I had to clean up.
 
I use a 1ohm RC filter which makes it possible for me to drop over 3v in each rail.

My voltage is 91/92vpp during operation

My caps are new.

It is curious. The amp is stable and stayed in idle for 16 hours straight with no problem. Bias is stable.

What could be the reason for the current imbalance? I will replace the mosfet but I want to understand. Thermal contact problem?

Thanks
 
I use a 1ohm RC filter which makes it possible for me to drop over 3v in each rail.

My voltage is 91/92vpp during operation

What could be the reason for the current imbalance? I will replace the mosfet but I want to understand. Thermal contact problem?

Thanks

Your measurements are in contrast to the specs of your tranny and elcaps you wrote in your opening post and let me assume that your tranny has secondaries with 2 x 33 VAC.
Besides this I don't think you have a thermal problem with this MosFet. I think that its matching was not optimal. Hope for you that you can get a better matched substitute.
 
Thank you.... what would be the audible effects of:

1) blown mosfet

2) mosfet not in shortcircuit but not working?

Thanks

i had a blown output on one of my aleph2's (not shorted, just dead) weeks went by before i discovered it. the only way i discovered it was that the heatsink seamed cold right in that output area. so i checked the voltage over that Source resistor. and sure, it was 0.00mV. the other 5 transistors was at a little under 600mV at that time. wich is a raise of about 100mV pr fet *5 fets. its easy to calculate that the total current flow was exatly the same as With 6 outputs:)
 
I replaced the mosfet. The values are now correct. 540mV on each resistor. There is still some variance but I think it is because of crap resistors (will order 1% soon)

The boards and circuit is here:

Pass Labs ALEPH-2 DIY amplifier PCB

another questions. I used a pot in place of the 56,2k resistor to change bias. I turned it all the way so that there is maximum resistance (maximum bias). The strange thing is that initially when the amp is turned on the bias levels are low: 2.7v on the RC 1ohm resistors so 2.7A then it varies for some time. I haven't had time to allow the amp to stabilize but is it normal such behaviour?

what is the bias behaviour before the amp fully stabilizes? Does it vary a lot?

Thanks!
 
I will :)

So just to be sure: largely varrying values are ok when cold. Offset can be high at frst (good to hear). Bias can be low in the beginning and then increase with time.
Correct?

I am afraid equilibrium is an issue. My heatsinks are 60x60x10cm and weigh 30kg each. I am afraid I migh have exagerated!
 
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