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Old 24th November 2007, 10:35 PM   #1521
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Hey jacco,


How do you feel about cross matching power fets between the top and lower rails?
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Old 24th November 2007, 11:06 PM   #1522
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Mr C,

i'd use 240s on top and 9140s down below.

My last 2 amputee projects had complementary vert. mosfets PP output stages, JAM's Mosfet A40 and Mr Greg Ball's GB50d, both run in full Class A.
On both, switching from IRFP9240 to the lower voltage capable 9140 was a major improvement.
I think it's a darn shame for the F4 to breathe on 9240s.
Now, where are the bigguns ?

(i is an oddball, at some point it gets easier to live with)
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Old 24th November 2007, 11:32 PM   #1523
DaveM is offline DaveM  United States
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I just had an amazing experience. I live in a town of 2000 people in Vermont. Our local hardware store/lumber yard is also a Radio Shack. I walked in there at 5 pm on a Saturday night and was able to walk out with a fist full of the appropriate resistors to make my F-4's match the updated schematic.

It is amazing to me that I was able to do that. Well, back to the man cave as my wife calls it. I have my own room too. 16' X 32'. Unfinished, but concrete walls and floor are the beginnings of a killer listening room. I do have my system set up in it presently and the size and layout of the room make it better than I've had before. I'm afraid that if I waited to do my F4 until it was done, I would never finish it.
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Old 24th November 2007, 11:45 PM   #1524
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16 x 32....

You could build one heck of a bass horn in one end of that bad boy!

I'm so sick of cluttering up the great-room that I absolutely must finish my hobby room before starting any other project. Now that winter's approaching, I know that if I begin the F4, there will be no stopping..... like ahh....what hobby room?


Congrats with locating those resistors on short notice.
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Old 24th November 2007, 11:52 PM   #1525
Magura is offline Magura  Denmark
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Quote:
Originally posted by jacco vermeulen
Mr C,

i'd use 240s on top and 9140s down below.

My last 2 amputee projects had complementary vert. mosfets PP output stages, JAM's Mosfet A40 and Mr Greg Ball's GB50d, both run in full Class A.
On both, switching from IRFP9240 to the lower voltage capable 9140 was a major improvement.
I think it's a darn shame for the F4 to breathe on 9240s.
Now, where are the bigguns ?

(i is an oddball, at some point it gets easier to live with)

Actually my experience is that the IRFP140 can take more abuse as well....so changing 240 to 140 is sure a win-win.

Magura
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Old 25th November 2007, 12:21 AM   #1526
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Quote:
Originally posted by jacco vermeulen

i'd use 240s on top and 9140s down below.


I like the 140s as well...

But why the 240s up top? (serious question)
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Old 25th November 2007, 12:40 AM   #1527
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I didn't get quite the answer I wanted.

Is there any benefit in matching the P channel power fets to N channel? Will the offset be easier to dial in if matched?
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Old 25th November 2007, 01:00 AM   #1528
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by carpenter
I didn't get quite the answer I wanted.

Is there any benefit in matching the P channel power fets to N channel? Will the offset be easier to dial in if matched?

benefit is in certainly better symmetry between upper and lower part of signal , when amp leaves portion where it works in A class .


setting offset isn't even slightly easier to set , in case of super duper everything matched .....

but- for real benefit - matching of lower and upper part of amp must be dynamic, not static ............ so - just forget about it ..........
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Old 25th November 2007, 01:05 AM   #1529
Magura is offline Magura  Denmark
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Quote:
Originally posted by Zen Mod



benefit is in certainly better symmetry between upper and lower part of signal , when amp leaves portion where it works in A class .


setting offset isn't even slightly easier to set , in case of super duper everything matched .....

but- for real benefit - matching of lower and upper part of amp must be dynamic, not static ............ so - just forget about it ..........

Wouldn't the only theoretical benefit be perfectly symetrical clipping?


Magura
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Old 25th November 2007, 01:13 AM   #1530
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Good. So, there's little chance that a mismatch between N and P can be causing Dave's offset problems?

Thanks guys.
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