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Old 15th February 2012, 05:10 PM   #91
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No square root here.

For staying class A you need twice the current into 4 ohms than into 8 ohms.
Example
25v rails
50w classA 4 ohms
Twin outputs biased 1.3 each.

33v rails
100w class A into 4 ohms
Four outputs biased 0.85A each
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Old 15th February 2012, 05:17 PM   #92
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Tanks Bobodioulasso
so to keep dissipation for each mosfets below 50W with 33 V rails I can bias them to about 1.5 A
and they stay in class A even if speaker impedence get down to 2 Homs.

Do one realy need the diodes?
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Old 15th February 2012, 06:14 PM   #93
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Dissipation as long as you stay in class A is
25x1.3=32.5w
or 33x0.85=28.05w
then it continues to increase when you leave classA because of a lower impedance load.
Quote:
and they stay in class A even if speaker impedence get down to 2 Homs.
No.

Last edited by bobodioulasso; 15th February 2012 at 06:16 PM.
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Old 15th February 2012, 06:24 PM   #94
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1.5A per device is ~0.7V drop across a 0R47 drain resistor, and ~1W dissipation.
Don't need no stinkin diodes.

Stays in Class A if it has 4 outputs in parallel.
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Old 15th February 2012, 06:42 PM   #95
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33v rails?



edit:
Where is it said 50w per device?

Last edited by bobodioulasso; 15th February 2012 at 06:55 PM.
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Old 15th February 2012, 06:53 PM   #96
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If BlackSabby wants 400W dissipation, that's what he gets.

(as me did with KSA50)
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Old 15th February 2012, 07:22 PM   #97
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Quote:
Originally Posted by bobodioulasso View Post
33v rails?



edit:
Where is it said 50w per device?


Just qoting Papa Pass
" You can get 50 W dissipation out of the big ones and about 40 of litle ones"
refering to sizez of mosfuses
can't remember from where but that bit stuck.

then one thing to tink do one realy need to stay in class A till the amplifier start volt clipping.

And I need to save for bigher trafos 24 V Ac out is bit low now.
Or wait for F6

Last edited by Bksabath; 15th February 2012 at 07:25 PM.
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Old 15th February 2012, 07:44 PM   #98
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Generally, for very low impedance loads one choose lower rails.

Leaving classA is not a problem neither.
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Old 15th February 2012, 08:05 PM   #99
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Quote:
Originally Posted by jacco vermeulen View Post
If BlackSabby wants 400W dissipation, that's what he gets.

(as me did with KSA50)
I had baby Krell 400 Xi and did not like it
bit like nails on black board.
I know the 50 are different beast but...
Compare that (400) to a F5 one should be rightly proud to have built as first outing on power deviece field.

yeah 400W dissipation is quite right

but in theory with sink large enoug or one maybe 2 of those in drawing one could
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Old 15th February 2012, 08:12 PM   #100
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Quote:
Originally Posted by bobodioulasso View Post
Generally, for very low impedance loads one choose lower rails.

Leaving classA is not a problem neither.
so one would agree with me, lets stick to one thing just to simplify 33 V rails, to agree with Jaco no need for stink diodes.
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