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Some other Source Follower Configurations
Some other Source Follower Configurations
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Old 11th August 2017, 01:43 PM   #491
ElFishi is offline ElFishi  Europe
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Here's another source follower:

A JFET Triadtron after John Broskie. It has a Zout of 28 mOhm (mind the milli). I prefer my BF862 to be cascoded as they tend to gate leak with higher Vds.

Let me know your thoughts.
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Old 11th August 2017, 04:39 PM   #492
EUVL is offline EUVL  Europe
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Do you think it will be DC stable ?


Patrick
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Old 11th August 2017, 09:14 PM   #493
ElFishi is offline ElFishi  Europe
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Sim says DC drifts with temperature, if that's what you mean.

A test circuit has a bug and currently I don't have time to hunt it down.
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Old 11th August 2017, 09:32 PM   #494
EUVL is offline EUVL  Europe
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Many of these circuits, including the TCS, do not always justify their complication when driving high impedance loads.
You can achieve the same performance by just using 2 pairs of matched NJFET in parallel.
And they, when thermally coupled, have very stable DC.

They come to play when you want to drive 30 ohm loads, as in the DAO.


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Old 11th August 2017, 10:27 PM   #495
ElFishi is offline ElFishi  Europe
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I've come to play with low Z buffers when ZenMod said you need one for his IronPre. But I'm not clear how low it needs to be.
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Old 11th August 2017, 10:51 PM   #496
EUVL is offline EUVL  Europe
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A TCS follower is push-pull, like a complementary follower.
So it halves the Zout of a NJFET follower.
Using 2 pairs of NJFET in parallel achieves the same.
The only difference is even harmonic cancellation in push pull.

My first DIY preamp using 5 pairs of 2SK170/2SJ74 in parallel.
Zout is < 3 ohm.


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Old 12th August 2017, 03:44 AM   #497
kinku is online now kinku  United States
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Quote:
Originally Posted by EUVL View Post
Many of these circuits, including the TCS, do not always justify their complication when driving high impedance loads.
You can achieve the same performance by just using 2 pairs of matched NJFET in parallel.
And they, when thermally coupled, have very stable DC.

They come to play when you want to drive 30 ohm loads, as in the DAO.


Patrick
The reason why I got attracted to TCS follower is predominant Second harmonic distortion.
What is the type of distortion in B1 and 2 Pairs of matched Jfets in parallel? Anyone measured or simulated them?
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Old 12th August 2017, 04:01 AM   #498
EUVL is offline EUVL  Europe
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Use Spice.


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Old 12th August 2017, 04:56 AM   #499
kinku is online now kinku  United States
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Patrick ,the current sensing SE NJFET follower also uses Push pull topology?does it uses NFB?
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Old 14th August 2017, 11:26 PM   #500
ElFishi is offline ElFishi  Europe
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Quote:
Originally Posted by EUVL View Post
Do you think it will be DC stable ?


Patrick
OK, for all practical purposes it is DC stable. But it needs a capacitor between base and collector of Q1 to not oscillate. I used 1nF.
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