mosfets, why the big ones

jjacks4x · 13th December 2002, 06:34 AM

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?

janneman · 13th December 2002, 06:41 AM

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

Circlotron · 13th December 2002, 07:06 AM

I think jjacks4x means why medium power fets for small signal use.

jh6you · 13th December 2002, 08:13 AM

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

janneman · 13th December 2002, 08:20 AM

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

uli · 13th December 2002, 09:34 AM

Good morning!
IMHO:
1) the noise floor is lower.
2) devices with higher transconductance lead to less distortion
without feedback.
Uli

jjacks4x · 13th December 2002, 04:29 PM

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

Nelson Pass · 13th December 2002, 07:51 PM

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.

Circlotron · 15th December 2002, 02:32 AM

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.

jackinnj · 15th December 2002, 02:51 AM

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

13th December 2002, 06:34 AM	#1
jjacks4x diyAudio Member Join Date: Oct 2002 Location: san jose	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?

13th December 2002, 06:41 AM	#2
janneman diyAudio Member Join Date: May 2002 Location: Where Germany, The Netherlands and Belgium meet Blog Entries: 6	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

13th December 2002, 07:06 AM	#3
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	I think jjacks4x means why medium power fets for small signal use. __________________ Best-ever T/S parameter spreadsheet. http://www.diyaudio.com/forums/multi...tml#post353269

13th December 2002, 09:34 AM	#6
uli diyAudio Member Join Date: Dec 2002 Location: Vienna, Austria	Noise floor Good morning! IMHO: 1) the noise floor is lower. 2) devices with higher transconductance lead to less distortion without feedback. Uli __________________ 'Jazz is not dead, it just smells funny' F.Zappa

13th December 2002, 04:29 PM	#7
jjacks4x diyAudio Member Join Date: Oct 2002 Location: san jose	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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13th December 2002, 08:13 AM	#4
jh6you Account Disabled Join Date: Aug 2002 Location: Near to the Pacific Ocean	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

13th December 2002, 08:20 AM	#5
janneman diyAudio Member Join Date: May 2002 Location: Where Germany, The Netherlands and Belgium meet Blog Entries: 6	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

15th December 2002, 02:32 AM	#9
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	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. __________________ Best-ever T/S parameter spreadsheet. http://www.diyaudio.com/forums/multi...tml#post353269

15th December 2002, 02:51 AM	#10
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	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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