Zen -> Cen -> Sen, evolution of a minimalistic IV Converter - Page 11

EUVL · 9th September 2011, 03:11 AM

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

Joachim Gerhard · 9th September 2011, 03:56 AM

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 ?

EUVL · 9th September 2011, 04:04 AM

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

EUVL · 9th September 2011, 06:35 AM

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

Joachim Gerhard · 9th September 2011, 09:38 AM

This outcome may surprise some. Adding resistors lowers noise, but thats the way constant current sources and mirrors work.

MiiB · 9th September 2011, 09:47 AM

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

Piersma · 9th September 2011, 09:54 AM

Just for the fun, a(nother) BJT version.

EUVL · 9th September 2011, 10:10 AM

> could I ask you to post the LTspice circuit

You mean you want our asc files ?

EUVL · 9th September 2011, 10:15 AM

Some more noise simulations for the original SEN & CEN.
Hard to beat a pair of FETs on their own.

Patrick

MiiB · 9th September 2011, 10:17 AM

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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9th September 2011, 03:11 AM	#101
EUVL diyAudio Member Join Date: Oct 2003	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

9th September 2011, 03:56 AM	#102
Joachim Gerhard diyAudio Member Join Date: Mar 2009	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 ?

9th September 2011, 04:04 AM	#103
EUVL diyAudio Member Join Date: Oct 2003	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

9th September 2011, 09:38 AM	#105
Joachim Gerhard diyAudio Member Join Date: Mar 2009	This outcome may surprise some. Adding resistors lowers noise, but thats the way constant current sources and mirrors work.

9th September 2011, 09:47 AM	#106
MiiB diyAudio Member Join Date: May 2005 Location: Denmark	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

9th September 2011, 10:10 AM	#108
EUVL diyAudio Member Join Date: Oct 2003	> could I ask you to post the LTspice circuit You mean you want our asc files ?

9th September 2011, 10:17 AM	#110
MiiB diyAudio Member Join Date: May 2005 Location: Denmark	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...