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Joachim Gerhard 29th July 2014 09:18 PM

I gave you the precedence.
I have connected 100pf to the output. I can try more.

Joachim Gerhard 29th July 2014 09:20 PM

I give in for today. Have to listen to some music....

FdW 30th July 2014 11:06 AM

Quote:

Originally Posted by as_audio (https://www.diyaudio.com/forums/analogue-source/154210-mpp-post4006929.html#post4006929)
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).

FdW 30th July 2014 11:13 AM

Quote:

Originally Posted by as_audio (https://www.diyaudio.com/forums/analogue-source/154210-mpp-post4006913.html#post4006913)
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.

as_audio 30th July 2014 11:43 AM

Quote:

Originally Posted by FdW (https://www.diyaudio.com/forums/analogue-source/154210-mpp-post4007476.html#post4007476)
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.

FdW 30th July 2014 01:26 PM

Quote:

Originally Posted by as_audio (https://www.diyaudio.com/forums/analogue-source/154210-mpp-post4007510.html#post4007510)
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 :)

as_audio 30th July 2014 02:21 PM

Quote:

Originally Posted by FdW (https://www.diyaudio.com/forums/analogue-source/154210-mpp-post4007591.html#post4007591)

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?

as_audio 30th July 2014 02:55 PM

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.

Joachim Gerhard 30th July 2014 04:09 PM

The gate stoppers have solved the oszillation.
I know, this thread was never easy to follow.
I now test the alternative offset cancelation.

FdW 30th July 2014 04:11 PM

Quote:

Originally Posted by as_audio (https://www.diyaudio.com/forums/analogue-source/154210-mpp-post4007668.html#post4007668)
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.


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