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AAAudio 21st January 2013 01:50 PM

Aleph 2 uneven temperatures
 
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

Zen Mod 21st January 2013 03:11 PM

check voltages across each source resistor

write down and post here

post exact schematic you;re using and write voltages by nomenclature

AAAudio 21st January 2013 05:03 PM

Thank you.... what would be the audible effects of:

1) blown mosfet

2) mosfet not in shortcircuit but not working?

Thanks

hm4nine 21st January 2013 07:28 PM

Alpeh 2 uneven temperatures
 
Quote:

Originally Posted by AAAudio (Post 3336091)
Thank you.... what would be the audible effects of:

1) blown mosfet

2) mosfet not in shortcircuit but not working?

Thanks

ad 1) Blown fuse, dead channel and/or destroyed woofer
ad 2) Less current capability, more destortions, worse sound

Zen Mod 21st January 2013 09:31 PM

yup

AAAudio 21st January 2013 11:07 PM

I measured voltage across source resistors.

The ccs mosfets measure 470-480mV on avergae but one measures 840mV! The gain devices measure 540mV more or less. No strange readings.

Is this behaviour common for bad mosfet?

Right now I have 130mV of DC offset. To much.

Zen Mod 21st January 2013 11:20 PM

power off

pull out that mosfet and source resistor

put new ones

hm4nine 22nd January 2013 05:42 AM

1500v toroid 0-44vx2
6x 69000uf 50v capacitors + 1 ohm RC filter


BTW:
Secondaries of your tranny are much too high; they should be around 2 x 33 VAC. Or voltage rating of elcaps should be 63 VDC, better 75 VDC.
There you will get your next problem.....

Gyuri 22nd January 2013 05:52 AM

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.

Gyuri 22nd January 2013 05:56 AM

hm4nine, you are ahead of me! :)


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