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Old 9th September 2011, 04:11 AM   #101
EUVL is offline EUVL  Europe
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For Joachim's circuit in post #99, THD is 0.0016% in Spice.

- Without 4x 370R loading resistor, THD is improved to 0.0012% for lesser voltage swing at input FET drains.
- Without the 4 helper BJT, THD is increased to 0.003%.
- Without 2x 50k feedback resistor is THD is 0.0021%.

So plenty of choices, whether to go for simplicity or the last few dBs THD.
We'll stay with the Wilson mirror for now.

I think I had a thinking error with Calvin's circuit. I think I get it now about the biasing.
My apologies to Calvin.
Still, my prejudice remains against exponential devices.
But I guess the real test is a listening test.
See if I have time to put a proto board together, using 3 separate supplies.


Patrick
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Old 9th September 2011, 04:56 AM   #102
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Thanks for simulating. I only have simple math in my toolbox. I studied electronics in the 70th where even a pocket calculator was forbidden. I failed my promise by a factor of two. Could it be that noise performance could be compromised without the loading resistors ?
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Old 9th September 2011, 05:04 AM   #103
EUVL is offline EUVL  Europe
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Joachim,

A member of my team did the sim, not me ....

I think it is just simple Spice with perfect resistors, so noise is not taken into account.
If you want to know more, please send me a email via the forum.
I'll get you in touch with him directly so that you don't have to talk via me.

Of course I want to be on the copy list to know what is going on ...
Shall be travelling tomorrow, so no email then.


Patrick
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Old 9th September 2011, 07:35 AM   #104
EUVL is offline EUVL  Europe
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Noise plot of Joachim's circuit.

Upper trace, without load resistors. Lower trace, with load resistors.

Joachim is right of course.
Noise performance is much better with load resistors.


Patrick
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File Type: png cen-iv-cm-jg-sim-noise-20110909.png (65.6 KB, 1220 views)
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Old 9th September 2011, 10:38 AM   #105
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This outcome may surprise some. Adding resistors lowers noise, but thats the way constant current sources and mirrors work.
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Old 9th September 2011, 10:47 AM   #106
MiiB is online now MiiB  Denmark
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Euvl ..

could I ask you to post the LTspice circuit...in a zipped folder.. would like to play a little with that and Joachim's RIAA...based on the same Idea...

Thanks
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Old 9th September 2011, 10:54 AM   #107
Piersma is offline Piersma  Netherlands
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Default Another BJT version

Just for the fun, a(nother) BJT version.
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File Type: png BJT- I-V ver1.2.PNG (109.4 KB, 1175 views)
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Old 9th September 2011, 11:10 AM   #108
EUVL is offline EUVL  Europe
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> could I ask you to post the LTspice circuit

You mean you want our asc files ?
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Old 9th September 2011, 11:15 AM   #109
EUVL is offline EUVL  Europe
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Some more noise simulations for the original SEN & CEN.
Hard to beat a pair of FETs on their own.


Patrick
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File Type: png sen-iv-noise-20110909.png (70.0 KB, 1116 views)
File Type: png cen-iv-noise-20110909.png (67.4 KB, 1094 views)
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Old 9th September 2011, 11:17 AM   #110
MiiB is online now MiiB  Denmark
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Yes.. I can see you have the models for the small transistors.. I have already modeled the circuit, but have some trouble with the balance.. would like to see how that changes with your small transistor models...
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