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Old 1st May 2004, 03:19 AM   #1
thanh is offline thanh  Viet Nam
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Default wanted a dual differential amplifier with all fet

Hi!I like JFET and MOSFET.I want to have a dual differential power amplifier with all FET.
I need all your hepl.Thanks you!
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Old 1st May 2004, 04:23 AM   #2
fab is offline fab  Canada
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Default Re: wanted a dual differential amplifier with all fet

Quote:
Originally posted by thanh
Hi!I like JFET and MOSFET.I want to have a dual differential power amplifier with all FET.
I need all your hepl.Thanks you!

See http://www.borbelyaudio.com/index31.htm and enjoy!

Erno Borbely is the original designer of Hafler DH-200 amp.
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Old 2nd May 2004, 02:03 AM   #3
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The Borbely amp has a dual (complementary) differential input stage. If you want an amp that is complementary differential from input to output, check out:

http://www.diyaudio.com/forums/showt...ht=#post334963

(At then end of the post is a zip file that you can download.)

Also, James Bongiorno had a design in Audio Amateur about 20 years ago (Ampzilla 200???) that was complementary differential from input to output, although it was 100% bipolars.
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Old 2nd May 2004, 03:03 AM   #4
thanh is offline thanh  Viet Nam
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Borbely's project has not got value of components.I is not good at designing JFET.Thank Charles Hansen and fab!
I still need that so i still need all your help!Again,thanks a lot!
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Old 2nd May 2004, 04:00 AM   #5
fab is offline fab  Canada
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Quote:
Originally posted by thanh
Borbely's project has not got value of components.I is not good at designing JFET.Thank Charles Hansen and fab!
I still need that so i still need all your help!Again,thanks a lot!

Maybe you did not check in the proper site menu. Check in more precisely in http://www.borbelyaudio.com/index15.htm. There are the "SERVO-50" and "DC-102". It includes all information including value of components.
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Old 2nd May 2004, 12:56 PM   #6
jcx is offline jcx  United States
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disctete FETs are really not good in "cookbook" projects, even professional engineers avoid them in mass production designs because of the wide individual and lot-to-lot parameter variations - simply copying a circuit based on fet part # alone could easily leave you with something that doesn't work at all due to bias errors

for diy and "hand crafted" audiophile projects they can be good but you must know enough to measure sort/match and individually trim bias as appropriate for each stage in your circuit
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Old 3rd May 2004, 12:18 AM   #7
fab is offline fab  Canada
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Quote:
Originally posted by jcx
disctete FETs are really not good in "cookbook" projects, even professional engineers avoid them in mass production designs because of the wide individual and lot-to-lot parameter variations - simply copying a circuit based on fet part # alone could easily leave you with something that doesn't work at all due to bias errors

for diy and "hand crafted" audiophile projects they can be good but you must know enough to measure sort/match and individually trim bias as appropriate for each stage in your circuit
Yes, and that is why I have indicated the "SERVO-50" and "DC-102" which only includes jfets at the input stage.
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Old 3rd May 2004, 04:31 AM   #8
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Borbely's project are way over priced. Heck you can buy a used Krell or a Levinson off eBay for what this guy want for his parts.
I believe that www.audioXpress.com still have some of his PCB's from passed project. You could change inputs from bipolars to FET that's is not a big deal.

Now if we only could get Charles Hansen to offer a PCB for his no feeback amp design, that would be cool.
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Old 5th May 2004, 06:12 AM   #9
thanh is offline thanh  Viet Nam
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this is JFET's formula.
Is not it a absolute formula?
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Old 5th May 2004, 01:29 PM   #10
jcx is offline jcx  United States
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a fine formula, but still an approximation that is limited to large Vds and “long channel” fets

the problem is that Idss and Vp can vary 5:1 for the same part # between batches - and smaller but still significant variations within a lot

you have no guarantee that you can select what you want yourself from any given lot of the same part # fet

you can buy fets sorted by the manufacturer to smaller ranges but fets are inherently more sensitive to normal process variations than most of the bipolar Q we use
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