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Old 4th June 2007, 01:16 AM   #641
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Would two BOSOZ's in series drive the F4 enough to power regular speakers as well as say, Aleph 30's
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Old 4th June 2007, 05:13 PM   #642
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How about using a couple of LM3875 as preamp? With one of them inverting it should be possible to run the F4 balanced. Maybe...



Iwahn
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Old 4th June 2007, 06:21 PM   #643
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by iwahn
How about using a couple of LM3875 as preamp? With one of them inverting it should be possible to run the F4 balanced. Maybe...



Iwahn

that can't be on par with F4
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Old 4th June 2007, 06:26 PM   #644
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Much better would be the LME49810... Just tie sink and source.
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Old 15th June 2007, 08:42 AM   #645
Variac is offline Variac  United States
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Nelson,
Since the F4 seems to exist , how about an actual photo of it?
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Old 15th June 2007, 02:00 PM   #646
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I thought all the First Watt product used the same chassis...assuming that the gears of my cognition have not stripped (no guarantees), it'll look the same as the other fellas.

Grey
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Old 15th June 2007, 04:44 PM   #647
Variac is offline Variac  United States
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I specifically asked because this one seems to need a LOT of heatsink- more than most of the previous amps I think? Members seem to be happiest with heatsinks that are almost 30x30 by 50 cm per channel I believe and that's a lot bigger than the typical First Watt chassis I think.

If in fact Nelson uses the same heatsinks as before, with their horizontal orientation, it shows that the requirements are not quite as onerous as implied..

PLus the face plate will look different....
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Old 15th June 2007, 05:49 PM   #648
steenoe is offline steenoe  Denmark
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Quote:
Originally posted by Variac
I specifically asked because this one seems to need a LOT of heatsink- more than most of the previous amps I think? Members seem to be happiest with heatsinks that are almost 30x30 by 50 cm per channel I believe and that's a lot bigger than the typical First Watt chassis I think.

If in fact Nelson uses the same heatsinks as before, with their horizontal orientation, it shows that the requirements are not quite as onerous as implied..

PLus the face plate will look different....
As far as I recall the F4 actually dissipates a bit less than the usual SE/CCS amps from NP. Approx 80 watts per channel.
Usually this figure is 100 watts.

Steen
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Old 15th June 2007, 05:50 PM   #649
Jaac is offline Jaac  Netherlands
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Let's say 2 amps bias per SE channel bij 44 volt is 88 Watt in class A to dissipate in a heatsink. So lets see the specs for thermal resistance of a irfp240
Tj-c =0,83K/W, Tc-s = 0.24K/W 0,5 K/W for an isolation plate and lets put al six on one 0,3 K/W heatsink (200mm SK56 from fisher).
Thats 1,8K/W best for a single FET. Gives me a total of 3.37K/W from junction to ambient.
One FET dissipates 88/6 Watt multiplie that by the 3,37K/W gives 49,4 K above ambient for the junction temp.
I think or was it to quick and simple ??
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Old 15th June 2007, 06:45 PM   #650
Variac is offline Variac  United States
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That fiendish Nelson seems to design his projects to fit the case!
Actually I'll bet he figured that first Watt will probably never exceed 25w/ch class A and ordered the case from there..
Ok OK - I guess I now know what it will look like....

Best advice on the heatsinks was "Crank up the bias until its at max allowable temp" Then I guess you can measure the bias and decide if that's enough. There never seems to be "too much"
If not enough: mas heatsink.
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