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Old 22nd September 2010, 08:48 PM   #1
Bensen is offline Bensen  Belgium
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Default 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).
Fully complementary FET-in FET-out design

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
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Old 22nd September 2010, 09:08 PM   #2
wahab is offline wahab  Algeria
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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.
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Old 22nd September 2010, 09:45 PM   #3
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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.
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Old 23rd September 2010, 07:15 AM   #4
Bensen is offline Bensen  Belgium
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Quote:
Originally Posted by darkfenriz View Post
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
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Old 23rd September 2010, 07:47 PM   #5
Bensen is offline Bensen  Belgium
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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
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Old 23rd September 2010, 09:03 PM   #6
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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.
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Old 11th October 2010, 07:01 PM   #7
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Quote:
Originally Posted by Bensen View Post
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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