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Old 29th July 2014, 09:18 PM   #10001
Joachim Gerhard is offline Joachim Gerhard  Germany
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I gave you the precedence.
I have connected 100pf to the output. I can try more.
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Old 29th July 2014, 09:20 PM   #10002
Joachim Gerhard is offline Joachim Gerhard  Germany
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I give in for today. Have to listen to some music....
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Old 30th July 2014, 11:06 AM   #10003
FdW is offline FdW  Netherlands
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Quote:
Originally Posted by as_audio View Post
Connect 1000 pF to the output to simulate a long coaxial cable and it will likely oscillate again.
The simulation gives no indication of oscillations (even with 10000pF) when gate stoppers of 470ohm are applied (for the follower and the PSU cascode).
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Old 30th July 2014, 11:13 AM   #10004
FdW is offline FdW  Netherlands
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Originally Posted by as_audio View Post
An offset large a this, some drift and strange noises are hints to parasitic oscillation in many cases.
Mosfet Vgs values will vary, matching may be needed. The offset (after matching) can be trimmed by adding a resistor(Rs) in series with the mosfet source. Resistors up to 100ohm (I did not check larger values) do not show in the FFT analysis.
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Old 30th July 2014, 11:43 AM   #10005
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Quote:
Originally Posted by FdW View Post
The simulation gives no indication of oscillations (even with 10000pF) when gate stoppers of 470ohm are applied (for the follower and the PSU cascode).
Computer simulation has little to do with the real circuit.
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Old 30th July 2014, 01:26 PM   #10006
FdW is offline FdW  Netherlands
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Quote:
Originally Posted by as_audio View Post
Computer simulation has little to do with the real circuit.
Ahhh... you are telling me.

But it has something to do with the real thing, else why is simulation used at all?

If not for simulation, this circuit may have never existed.

Maybe a more positive contribution will be more helpful

Last edited by FdW; 30th July 2014 at 01:30 PM.
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Old 30th July 2014, 02:21 PM   #10007
as_audio is offline as_audio
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Quote:
Originally Posted by FdW View Post

Maybe a more positive contribution will be more helpful
JG talked about oscillation. That is the real thing and does not show up in simulation.
Frans, what kind of contribution are you looking for?
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Old 30th July 2014, 02:55 PM   #10008
as_audio is offline as_audio
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OK, some contribution.

I have a look at your right hand circuit in post 9981.

Mosfets 7 and 9 have the same n-channel designation, but different polarity in the diagram.

But it is not the same on the negative side. Two ZVP3306 (8 and 10) are shown, p-channel from the datasheet.

I can not read the diagram in 9986, it is too small, but may be the same.

It is a small error anyway but it can be confusing.
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Old 30th July 2014, 04:09 PM   #10009
Joachim Gerhard is offline Joachim Gerhard  Germany
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The gate stoppers have solved the oszillation.
I know, this thread was never easy to follow.
I now test the alternative offset cancelation.
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Old 30th July 2014, 04:11 PM   #10010
FdW is offline FdW  Netherlands
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Quote:
Originally Posted by as_audio View Post
OK, some contribution.

I have a look at your right hand circuit in post 9981.

Mosfets 7 and 9 have the same n-channel designation, but different polarity in the diagram.

But it is not the same on the negative side. Two ZVP3306 (8 and 10) are shown, p-channel from the datasheet.

I can not read the diagram in 9986, it is too small, but may be the same.

It is a small error anyway but it can be confusing.
The mosfet's are ZVN and ZVP 3306. As soon as Joachim is done testing (we are testing a new offset canceling solution) I will post a 'final' schema and .asc.

Last edited by FdW; 30th July 2014 at 04:14 PM.
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