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-   -   wanted a dual differential amplifier with all fet (http://www.diyaudio.com/forums/solid-state/33295-wanted-dual-differential-amplifier-all-fet.html)

thanh 1st May 2004 04:19 AM

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!

fab 1st May 2004 05:23 AM

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.

Charles Hansen 2nd May 2004 03:03 AM

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.

thanh 2nd May 2004 04:03 AM

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!

fab 2nd May 2004 05:00 AM

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.

jcx 2nd May 2004 01:56 PM

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

fab 3rd May 2004 01:18 AM

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.

jewilson 3rd May 2004 05:31 AM

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. :D

thanh 5th May 2004 07:12 AM

2 Attachment(s)
this is JFET's formula.
Is not it a absolute formula?

jcx 5th May 2004 02:29 PM

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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