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-   -   Mosfet's using in driver stage (http://www.diyaudio.com/forums/solid-state/174107-mosfets-using-driver-stage.html)

Bensen 22nd September 2010 07:48 PM

Mosfet's using in driver stage
 
As a rookie, I try to keep the number of stages as low as possible. This leaded me to the idea to use mosfet's as driver stage, to minimise the influence of the load to my previous stages without using a triple EF.

But, it looks very difficult to find any info on this topic.
Does anybody has some schematics as example to start from? The JC1 schematic would be great! ;)

I would like to use that driver stage behind a JFET (2SK389/2SJ109 input stage). The VAS stage with extra gain will not be a bad idea I think. See a previous thread which I posted before I started building my home (it's ready now).
http://www.diyaudio.com/forums/solid...ut-design.html

But instead of mosfet output stage I bought Sanken 2sc2922/2sa1216 BJT's which I would like to use. The dual Jfet's and dual bjt's I have already laying around.


Thanks
Ben

wahab 22nd September 2010 08:08 PM

This kind of topology, symetrical with cascoded differential VAS
is very good.

I also used it as a first step to improve an older design.

Just be careful to correctly compute the standing currents
and the compensation scheme and it will work perfectly.

darkfenriz 22nd September 2010 08:45 PM

I've tried bjt>mosfet>bjt tripple darfetlington output stage and it worked well. Not as fast and stable as mosfet output, but linearity was fine.

Bensen 23rd September 2010 06:15 AM

Quote:

Originally Posted by darkfenriz (Post 2311369)
I've tried bjt>mosfet>bjt tripple darfetlington output stage and it worked well.

Have you got a schematic of circuit? That could help me al lot.
What mosfet's did you used for drivers?
Thanks

Bensen 23rd September 2010 06:47 PM

1 Attachment(s)
I know John Curl used Mosfet's (2SK1530/2SJ201) as drivers in his JC1 (mentioned in this forum) and that accuphase uses also Mosfet's.

Still, 95% of all schematics I've seen have BJT's implemented as drivers. Can anyone help me to find out the advantages/disadvantages of using Mosfet's VS BJT's as drivers.

Advantage of Fet's
1. No influence from load on output
2. Less predriver/driver stages needed in general
3. Faster than BJT's
4. ??


Disadvantage
1. Higher input capacitance
2. ??



Greetz
Ben

richie00boy 23rd September 2010 08:03 PM

Hi, I have the perfect amp for you. I just made two PCBs for a friend last night as it happens, now that I have the design working stable and sounding good. I will upload schematic later.

darkfenriz 11th October 2010 06:01 PM

Quote:

Originally Posted by Bensen (Post 2311717)
Have you got a schematic of circuit? That could help me al lot.
What mosfet's did you used for drivers?
Thanks

Followers, as simple as it gets.
2n5401/5551 to irf610/9610 to 2sa1943/c5200.
No further tricks.


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