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Old 21st January 2013, 01:50 PM   #1
AAAudio is offline AAAudio  United States
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Default 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
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Old 21st January 2013, 03:11 PM   #2
Zen Mod is offline Zen Mod  Serbia
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check voltages across each source resistor

write down and post here

post exact schematic you;re using and write voltages by nomenclature
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Old 21st January 2013, 05:03 PM   #3
AAAudio is offline AAAudio  United States
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Thank you.... what would be the audible effects of:

1) blown mosfet

2) mosfet not in shortcircuit but not working?

Thanks
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Old 21st January 2013, 07:28 PM   #4
hm4nine is offline hm4nine  Europe
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Default Alpeh 2 uneven temperatures

Quote:
Originally Posted by AAAudio View Post
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
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Old 21st January 2013, 09:31 PM   #5
Zen Mod is offline Zen Mod  Serbia
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yup
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Old 21st January 2013, 11:07 PM   #6
AAAudio is offline AAAudio  United States
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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.
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Old 21st January 2013, 11:20 PM   #7
Zen Mod is offline Zen Mod  Serbia
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power off

pull out that mosfet and source resistor

put new ones
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Old 22nd January 2013, 05:42 AM   #8
hm4nine is offline hm4nine  Europe
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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.....
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Old 22nd January 2013, 05:52 AM   #9
Gyuri is offline Gyuri  Hungary
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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.
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Old 22nd January 2013, 05:56 AM   #10
Gyuri is offline Gyuri  Hungary
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hm4nine, you are ahead of me!
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