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Old 13th December 2002, 06:34 AM   #1
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Default mosfets, why the big ones

I am sorry if this is a old point. But I am wondering what is the benifit of using large die mosfets ie:610, 9610 vs. small signal mosfets?
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Old 13th December 2002, 06:41 AM   #2
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Default mosfets

May I pose a counter question:

What is the use of a 6.6 litre engine in a Mustang vs a 2.2 litre engine?

Jan Didden
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Old 13th December 2002, 07:06 AM   #3
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I think jjacks4x means why medium power fets for small signal use.
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Old 13th December 2002, 08:13 AM   #4
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Probably, it is to get a good fit for designer's purpose.
If the size gave any benefit, it would be a second thought.

JH
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Old 13th December 2002, 08:20 AM   #5
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Well, OK, but the larger die's are used to get Ron down, but it does increase capacitances and lower bandwidth. For small-signal uses, normally the Ron is less important but the wider bandwidth is a plus. So each of the parts has a place where it is best suited.

Jan Didden
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Old 13th December 2002, 09:34 AM   #6
uli is offline uli  Austria
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Default Noise floor


Good morning!
IMHO:
1) the noise floor is lower.
2) devices with higher transconductance lead to less distortion
without feedback.
Uli
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Old 13th December 2002, 04:29 PM   #7
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Default thanks for your info

Thank you all for the info. My real motive is project size. I am redoing a sacd player and want to do a susy buffer stage. So using the "What did Nelson do method" I see only large die mosfets. And before I build something I like to get peoples take on different ways. Keeping the parts small is helpfull but sound is the most important to me. I just wondered if you could still get same sound style out of small die units?
Thanks again
John
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Old 13th December 2002, 07:51 PM   #8
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Default Re: Noise floor

Quote:
Originally posted by uli
1) the noise floor is lower.
2) devices with higher transconductance lead to less distortion
without feedback.
And you can bias them to higher currents for greater
drive and linearity.
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Old 15th December 2002, 02:32 AM   #9
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The fet I used for the low level part of my class A, an ST P3NB60 ( have lots of them, no other reason) is a TO-220 only good for a couple of amps and 600v, but at 50mA and Vds of 75v at 150v supply will swing 80v p/p with no visible distortion and 100v p/p with almost none, and is 3db down at 7MHz IIRC. It dissipates 3.75 watts doing this so you nead to heatsink it. Too much for a little tiddler fet. Thanks to Mr Pass for championing this method; I probably would never have tried it otherwise.
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Old 15th December 2002, 02:51 AM   #10
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Default Janneman - no 6.6L Mustang

there have been Mustang engines of 390, 392, 427, 428 and 429 cu inches, but no 402 (=6.6 L).
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